An Introduction to

Roofing and Painting

 

 

J. Paul Guyer, P.E., R.A.

Editor

 

 

 

 

 

 

 

 

 

 

 

 

 

The Clubhouse Press

El Macero, California

 

 

CHAPTERS

 

Chapter                                                                                                                                  Page

 

1.  ROOFING SYSTEMS                                                                                                    1

2.  COATINGS AND PAINTS                                                                                            52

3.  ANALYSIS OF PAINT FAILURES                                                                              101

4.   INSPECTION OF PAINTING OPERATIONS                                                          124

 

 

 

 

 

(This publication is adapted from the Unified Facilities Criteria of the United States government which are in the public domain, have been authorized for unlimited distribution, and are not copyrighted.)

 

(Figures, tables and formulas in this publication may at times be a little difficult to read, but they are the best available.  DO NOT PURCHASE THIS PUBLICATION IF THIS LIMITATION IS UNACCEPTABLE TO YOU.)

 

 

 

CHAPTER 1

ROOFING SYSTEMS

 

1. STARTING POINTS FOR ROOF SYSTEM SELECTION. This Chapter is intended to introduce the major considerations in selecting a roofing system. Figure 1 depicts the various alternative roofing systems and how they relate. When commencing the selection process there are two different starting points.

 

 

Material and Roofing System Options

Figure 1

1.1  New vs. Reroofing. The roof may be part of a new building design; or, it may involve the reroofing of an existing structure (replacement or re-cover). Today, approximately 75% of roofing activity is reroofing.

 

1.2  Steep-Slope vs. Low-Slope. In new construction the designer is very likely to have a preconceived notion as to whether a highly visible sloped-roof is wanted, or whether a less visible low-slope roof design is acceptable. Positive drainage is a very important design criterion. When reroofing, it may be feasible to improve drainage by using tapered insulation or sloped deck fills.

 

2. SELECTION CONSIDERATIONS FOR STEEP ROOFING SYSTEMS. Table 1 evaluates common steep roofing systems based upon some use criteria.

 

2.1  Aesthetics. Steep roof systems make a strong visible statement about a building. The texture, shadow-line, and color are major factors in selection.

 

2.2  Minimum Slope Requirements. Steep roofs function by shedding water rather than by being waterproof (Figure 2). Minimum slopes as shown in Table 13, are required in order to insure proper drainage.

 

2.3  Categories of Steep Roofing. Major categories of steep roofing include asphalt shingles, wood shingles and shakes, tile, slate, architectural metal, asphalt roll roofing, and fabricated units of metal or plastic intended to look like the others. Only asphalt roll roofing and asphalt or wood shingles may be re-covered.

 

2.4  Snowshedding and Ventilation. Sloped roofs are effective snowshedders. In addition, the attic space that accompanies steep roofing makes it easy to ventilate the roofing system.

 

Steep Roofing (hydrokinetic)

Figure 2

 

Low-Slope (hydrostatic)

Figure 3

2.5  Maintenance Requirements. Sloped roofs in general, require less maintenance than flat roofing systems.

 

2.6  Steep Roof Conversions. When considering reroofing a flat roof, it may be possible to convert the low-slope roofing system to a steeply sloped roof. This may improve the appearance of the building while resolving drainage problems as well. Steep roof conversions are a viable option for relatively narrow buildings.

 

Steep Slope Selection Based Upon Use Criteria

Table 1

 

3. SELECTION CONSIDERATIONS FOR LOW-SLOPE (MEMBRANE) ROOFING.

Membrane roofing is typically used on commercial buildings where the minimum slopes required by steep roofing render them impractical for larger buildings. Low-slope membrane systems are completely sealed at laps and flashings (Figure 3) and can temporarily resist standing water conditions. Choices for membrane roofing include multi-ply bituminous built-up (BUR), polymer-modified bituminous (MB), elastomeric single-ply systems (e.g., EPDM), thermoplastic single-ply systems (e.g., PVC or TPO), sprayed-in-place polyurethane foam (SPF), and some metal (hydrostatic/low-slope/SSSMR) systems. Designers frequently select low-slope roofs when the roof is expected to accommodate rooftop equipment. With the exception of foam and metal, all low-slope systems can be incorporated into Protected Membrane Roof (PMR) designs.

 

4.  REROOFING AND RE-COVERING.

 

4.1  Reroofing. The term replacement is used when the existing roofing system is to be either partially or totally removed and a new system installed. The designer should consider any existing problems and whether drainage and thermal performance needs to be improved.  Existing surfaces such as walls and curbs may be contaminated with bitumen, which might affect compatibility with some reroofing options. Additional concerns (as compared to new roofing) include whether the existing structure can handle a significantly heavier roof system and whether construction activities of the reroof system will affect the occupants of the building (i.e., fumes, falling debris, and noise).

 

4.2  Re-cover. The term re-cover is used when a new roofing system is to be superimposed directly over an existing system. In this case, underlying conditions are obscured making assessment of their condition more difficult. Additional concerns include how the re-cover system will be attached to the existing membrane or roof deck, and compatibility with the substrate. The potential for trapped water between the old and new membrane may suggest the use of venting base sheets and/or roof vents.

 

5.  ENVIRONMENTAL ISSUES. A relatively new design criterion is whether the roof system under consideration meets green criteria, such as whether the system incorporates postconsumer waste or is itself recyclable at the end of its useful life. Roof system waste is bulky and puts a great strain on waste disposal sites. Energy efficiency is also important in terms of raw materials acquired, production of finished goods, and application of the roof system. Thermal performance in service and retention of thermal value with age are equally important.  A sustainable or robust roof is highly desirable as extension of the life of the roof contributes to overall conservation. High albedo (reflective) roofs may improve localized climate conditions. The felt used in asphalt organic shingles consists primarily of recycled wastepaper, wood chips, and sawdust. Asphalt itself is a by-product of petroleum refining. Wood fiber and perlite roof insulation contain waste paper. Glass fiber and asphalt organic shingles have been recycled into asphalt curbing and the like. Wood shingles and shakes can be recycled into garden mulch.  Steel and aluminum contain recycled scrap and at the end of their life, metal panels can be recycled back into scrap. Tables 2 and 3 compare environmental considerations for steep and low-slope roofing systems.

 

 

Preserving the Environment – Steep Roofing

Table 2

Preserving the Environment – Low-Slope Roofing

Table 3

 

6.  DETAILED INFORMATION. Once a tentative roofing system selection has been made using information provided by this discussion.

 

7.  USING PRINCIPAL DESIGN CONSIDERATIONS TO REDUCE THE NUMBER OF POSSIBLE ROOF SYSTEMS.

 

7.1  Principal Design Considerations. Tables 4 and 5 list some of the principal design considerations in roof system selection. An explanation of the headings follows the tables. These tables are not all-inclusive but contain many criteria that the designer can consider to reduce the myriad of choices. Systems that fail to meet the principal project design criteria can be quickly disqualified from further consideration. For example, if an existing structure has reached its design load limit, then heavier roofs (such as ballasted single-ply roofs or concrete tiles) would have to be disqualified (or the structure would have to be strengthened at significant cost).

Principal Design Considerations—Steep Roofing

Table 4

 

Principal Design Considerations—Low-Slope Roofing

Table 5

7.2  Discussion of Headers in Tables 4 and 5.

 

7.2.1  Initial Cost. This may include materials, labor, and special set-up for construction.

Initial cost may determine if the roof, as designed, is affordable. Perhaps a somewhat less expensive system should be considered if it does not incur significantly increased maintenance costs or have a shortened life.

 

7.2.2  Life Cycle Cost. LCC considers durability but also presumes that routine

maintenance will be performed to achieve the projected life. Consider whether the building is temporary or permanent. It would be hard to justify an expensive copper or slate roof on a building scheduled for demolition in the near future. Also consider the mission of the building.  There are levels of quality in many systems. For example, while 45 mil EPDM is the standard, for little extra cost 90 mil material with greater puncture resistance, or conversion to a PMR system, could be specified for a building with a critical mission.

 

7.2.3  Construction Difficulty. Some systems require more clearance to accommodate

application methods and equipment. Large prefabricated roof sheets (i.e., 50 ft. by 200 ft.) may be fine on a large roof with few penetrations, but are impractical on a roof area that is broken up by many curbs and equipment supports. On multiple penetration surfaces, relatively narrow sheets (e.g., BUR, MB, thermoplastic single-ply) or sprayed-in-place polyurethane foam should be considered. Penetrations through standing seam metal roofing need to accommodate the expected thermal movement of the metal panels. Thermal movement is cumulative, increasing with distance from the point where the panels are restrained (typically the eaves).  Penetrations in SSSMR panels must pass through the flat portion of the panel, not through the standing seam. Penetrations wider than a single panel require a diverter to carry water around the obstruction. Water must flow parallel to the raised seams, never over them.

 

7.2.4  Periodic Maintenance—(The need for periodic maintenance and difficulty of

inspection or maintenance.) Some roof systems require periodic recoating for weather protection.  Aggregate surfaced roofs are more difficult to inspect and patch than smooth surfaced roofs.

 

7.2.5  Life Expectancy. A mean life is listed but the actual life is affected by drainage,

maintenance, and extreme use or abuse.

 

7.2.6  Suitability in Severe Cold. Effects of freeze-thaw, hail, ice scrubbing, and traffic while cold (i.e., snow removal) is considered. Some materials embrittle dramatically at low temperatures (i.e., have a relatively high glass transition temperature); others may embrittle as they weather and lose plasticizer or are degraded by UV or thermal load. H indicates highly suitable; L indicates less suitable.

 

7.2.7  Suitability in Extremely Hot or Humid Conditions. Effects of thermal expansion and algae growth are considered. H indicates more suitable, L indicates less suitable.

 

7.2.8  Wind Resistance. Roofs are vulnerable to wind scour and blow-off. While arbitrary ratings are provided here, the resistance is affected by building height, terrain, parapet height and measures taken to upgrade perimeter and corner attachment. H indicates highly wind resistant (when properly designed). For membrane roofing, impermeable roof decks such as cast-in-place concrete are best. Air retarders are needed with loose laid and mechanically fastened single-ply systems as they may otherwise balloon from interior air leakage. Perimeter wood blocking must be well anchored to prevent peeling of the membrane or loss of fascia metal. Avoid the use of small aggregate (e.g., pea gravel) near tarmacs and on skyscrapers due to the damage it can cause if blown off the roof by high wind. Asphalt shingles may require manual application of tab adhesive. Interlocking asphalt shingles provide excellent wind resistance. Metal panel systems are wind resistant only when all components including clips, fasteners, and secondary structural members are installed as wind-tested. SPF has outstanding resistance to wind and to wind-blown missiles. SPF roofs performed well in hurricane Andrew, especially when they were spray-applied

directly to concrete roof decks.

 

7.2.9  Resistance to Ponding Water. Membrane roof systems rely upon sealed seams to resist hydrostatic pressure. Water absorption may result in root or algae growth or cause rot. H infers highly resistant to these conditions.

 

7.2.10  Traffic Wear Resistance. Roofs that have a lot of rooftop equipment will have foot traffic that can cause punctures or abrasion. Most roof systems are available with traffic protective overlayers, such as walkways. H indicates highly resistant to abuse assuming protective courses have been used.

 

7.2.11  Resistance to Chemicals (resistance to oils, fats, grease, metal ions). Some roof surfaces are vulnerable to exhausted fumes or liquids. Thermoplastic polyolefins (TPO’s) and Hypalon® (CSPE) may be better than bituminous materials in resistance to oils, greases, and solvents. Copper-containing runoff water from condensate coils or flashings will corrode zinc and zinc-aluminum SSSMR roofing. H indicates better than average resistance to attack.

 

7.3  Weight Factor. Consider the total number of roofs already installed, the weight of the proposed roof system possible, and construction loads. The unit weight of membrane systems vary dramatically, ranging from less than 0.5 psf for a 2 in. thickness of SPF, to more than 20 psf for ballasted single-ply systems. Typical roof system weights and construction loads are shown in Table 6.

 

7.4  Compliance with Fire & Wind Requirements. Roofing systems are rated as entire systems, including the roof deck, method of attachment to the deck (e.g., fasteners, hot bitumen, cold adhesives), vapor retarder (if used), thermal insulation, roof membrane, and surfacing. Typical External Fire Ratings (ASTM E-108, Class A, B or C) are shown in Tables 7 and 8.  Combustible decks (wood/plywood/OSB) require selected combinations of underlayments, insulation, roofing, and surfacing to resist burning brands and intermittent flame as described in ASTM E108.

 

7.5  Roof Decking. Principle roof decks for membrane roofing include steel, cast-in-place concrete, precast concrete, wood, plywood, OSB, and structural wood fiber. Variations of cast-in-place concrete include lightweight structural concrete (typically 1680 kg/m3)(105 psf) and lightweight insulating concrete(480 kg/m3)(30 psf). In new design, the roof deck is generally selected based upon construction considerations and materials. Steel is by far the most popular, followed by concrete and plywood/OSB. Table 9 lists some criteria for deck selection for new construction. Table 9 lists methods of attachment to the roof deck. Attachment options include full adhesion, mechanical fastening, and loose-laid/ballasted roofing. Steel decking requires a

bridging course typically mechanically fastened roof insulation. For steep roofing, plywood and OSB roof decks are most common. They generally utilize flexible batts as underdeck roof insulation although architectural metal and cathedral ceiling constructions may use rigid insulation above the deck.

 

7.6  Suitability of the Membrane for the Substrate. Table 10 lists some possible

combinations.

Typical Weights of Material and Equipment

Table 6

Fire Ratings and Required Underlayments for Steep-Sloped Roof Systems

Table 7

 

Fire Ratings and Required Underlayments for Low-Slope Roof Systems

Table 8

Suitability of the Roof Deck for Various Conditions

Table 9

 

Membrane/Substrate Compatibility/Attachment Methods

Table 10

7.7  Thermal Insulation. Rigid thermal insulations used under membrane roofing include wood fiber, perlite fiber, glass fiber, foamed glass, polystyrene (extruded or expanded), and polyisocyanurate (isoboards). Non-structural thermal insulations include glass fiber and mineral wool batts, blown loose insulations such as cellulose fiber, glass fiber, mineral fiber, and expanded vermiculite. Table 11 indicates suitability of rigid roof insulations for membrane roofing based upon intended method of use.

Suitability of Roof Insulation for Method of Use

Table 11

 

7.7.1  Thickness of Insulation. If thick layers of insulation are needed to meet a high therm resistance, thicker wood nailers and deeper fascia metal will be required. Foam plastics such as polyisocyanurate and polystyrene have the highest R values per unit thickness.

 

7.7.2  Clearance of Metal Panels. In standing seam metal roof systems, the permissible thickness of blanket insulation may be limited by the clearance provided by the supporting clip design.

 

7.7.3  Insulated Attic. Blanket insulation used in steep roofing systems is frequently

placed on the floor of the attic where R-values of 30 (RSI = 5.4) or more may be possible (Figure 13).

 

7.7.4  Ceiling Insulation. Dropped ceilings are sometimes insulated by placing batts

directly above the ceiling panels. This practice is not recommended as subsequent access to underdeck equipment or phone wires is blocked. When the insulation is displaced to gain access it is rarely put back in place correctly, if at all.

 

7.8  Suitability for Extreme Climates. Protected membrane systems (PMRs) are very well suited to extremely cold climates and have been successfully used in all climates. For extreme conditions of snow and ice, a cold (ventilated) roof should be considered. For most steep roofing this is achieved by allowing a flow of outdoor air between the insulation and the roofing system.  This air cools the roof in summer, dries out any moisture that condenses in the roof, and greatly reduces the formation of icicles and ice dams along eaves. For regions prone to severe hail, ballasted EPDM roofs are very good and PMRs are excellent. Tiles, shingles, bare BUR, and metal systems are easily damaged by hail. In regions of semitropical climate (high temperatures and humidity), asphalt shingles should be treated to be fungus resistant and wood shakes/shingles should be pressure treated for rot resistance.

 

7.9  Installation in Cold or Wet Weather. Most membrane systems are difficult to install in subfreezing weather. If frequent precipitation during construction is a problem, factory fabricated single-ply systems with field welded seams may have advantages over systems where field application of adhesives or hot bitumen is needed. Torch applied modified bitumens are one of the few systems that can be applied, albeit slowly, in wet windy conditions.

 

7.10  Warranties. The NRCA Commercial Low-Slope Roofing Materials Guide contains a comprehensive side-by-side comparison of commercial roof warranties. The roofing industry offers two general types of warranties: Materials Only and Materials & Workmanship. Carefully read exclusions and limits. Note: The longest warranties are not necessarily the best, nor does the length of the warranty directly relate to roof durability. In many cases, manufacturers may restrict their warranties.

 

7.11  Maintenance Considerations. Sloped roofs require less routine maintenance and may be preferred when the facilities management is incapable of providing routine inspections and minor repairs. Modified bituminous and BUR systems may be superior in abuse resistance to thin single-ply systems. Various protection boards/walkways can be used around equipment where traffic is anticipated. Protected membrane roof systems (PMR’s) are abuse resistant but more difficult to inspect and repair.

 

7.12  Roof Access, Fumes and Property Protection When Reroofing.

 

7.12.1  Fumes. In reroofing situations fumes from kettles and solvents may be objectionable. Hot coal tar pitch is especially objectionable; hot asphalt is also noticeable but less noxious. Cold applied systems with taped or welded seams and metal roof systems generate few odors. It may be necessary to coordinate air-conditioning shutdown to avoid taking fumes into the occupied building.

 

7.12.2  Ease of Construction Access. If the area around the construction site is congested it may make heating and hoisting of roofing materials difficult.

 

7.12.3  Specifying Construction Procedures. Site access, material storage area, layout area, building and landscape protection should be identified on drawings.

 

7.12.4  Safety and Disturbance to Occupants. The presence of occupants, vehicles, and pedestrians may be of concern. Reroofing is noisy. Dust and overspray may affect those nearby.

 

7.13  Installation. Roofing requires skilled installers. Qualified contractors and inspectors are more likely to be available if the system is customarily used in the region. It should be determined whether there are several manufacturer-approved installers capable of bidding the work.

 

7.14  Owner Preferences. Verify that the contemplated system is acceptable to the owner, occupants, and maintenance personnel.

 

8.  CONSIDERATIONS WHEN SPECIFYING LOW-SLOPE (HYDROSTATIC) MEMBRANE ROOFING. With the exception of SSSMR, membrane roofing requires a suitable roof deck. Most constructions will also use thermal insulation. Vapor retarders are sometimes required to protect the roofing system from attack by interior moisture.

 

8.1  Built-up Roofing (BUR). BUR Consists of multiple reinforcements such as asphalt treated glass or organic felt laminated together with hot-applied bitumen (asphalt or coal tar pitch) or cold adhesives (Figure 4). Surfacings include aggregate, coatings, capsheets, and sprayed roofing granules. A typical system includes thermal insulation and may include a vapor retarder.

Typical BUR System

Figure 4

 

8.2  Polymer Modified Bitumen. MB consists of reinforcing sheets factory-coated with polymer modified bitumen. They may be laminated in the field using hot bitumen, heat fusion, or by cold adhesives (Figure 5). Surfacings include capsheets with mineral granules, metal foil, and field applied coatings.

Polymer-Modified Cap Sheet Adhered to Mechanically Fastened Base Sheet

Figure 5

 

8.3  Elastomeric (Single-Ply) Membranes. Elastomeric membranes consist of a factory produced sheet generally of EPDM rubber with seams field-sealed with adhesive or tape (Figure 6). Sheets are unsurfaced unless ballast is used. Elastomers are vulcanized (thermoset), and usually non-reinforced except when used in mechanically fastened systems. A fleece-backed sheet is also available for fully adhered systems when it is desired to use hot bitumen as an adhesive (e.g., for re-covering an asphalt-contaminated deck or old BUR).

EPDM Roof System

Figure 6

 

PVC Roof System

Figure 7

8.4  Weldable Thermoplastic Membranes. These membranes consist of a sheet of reinforced thermoplastic material such as PVC or TPO. Sheets are unsurfaced or ballasted. Seams are generally heat fused although solvent welding and adhesive bonding are also possible (Figure 7).

 

8.5  Structural Standing Seam Metal Roofing. SSSMR consists of metal panels with raised seams more than 1-1/2 in. high (Figure 8). Sealants are utilized at side seams and endlaps to provide waterproofing. Most are considered hydrostatic, resisting standing snow and occasional ponding. Caution: ridges and valleys of a SSSMR may not be as watertight as the seams.

Structural Standing Seam Metal Roofing

Figure 8

 

8.6  Sprayed-in-Place Polyurethane Foam. SPF is a thermoset rigid foam, field-formed by the reaction of liquid components (in the presence of a foaming agent) sprayed onto the substrate. SPF is protected by liquid-applied elastomeric coatings or an application of loose gravel (on slopes < 4%).

Components of Membrane Roofing System

Figure 9

 

8.7  Components of Membrane Roofing Systems (Figure 9).

 

8.7.1  The deck supports roofing loads and is selected to conform to fire resistant design classifications. Not all systems require a deck (e.g., structural standing seam metal roofing).

 

8.7.2  A vapor retarder protects the insulation against moisture vapor attack from the

warm, high vapor pressure side of the roof assembly. Not all buildings require a vapor retarder.

 

8.7.3  An air barrier prevents air movement (infiltration or exfiltration) through the roofing system.

 

8.7.4  Thermal insulation provides thermal resistance and prevents condensation on

components beneath the insulation. It also furnishes support and a smooth, continuous substrate for the membrane.

 

8.7.5  The membrane is intended to keep water out of the components below (as well as out of the building). The membrane system affects fire resistance.

 

8.7.6  Individual roofing components may be held in place by adhesives, fasteners, ballast, or a combination of these methods.

 

8.7.7  Perimeter flashings are waterproof vertical terminations of the membrane (perimeter flashing) (Figure 10).

Wall Base and Cap Flashing

Figure 10

 

8.7.8  Roof edging and fascia are usually low profile roof edge terminations and side trim.

 

8.7.9  Roof penetrations include drains, vents, curbs, equipment supports, and the like.

 

8.7.10  Surfacing materials screen UV light, improve fire ratings, and may improve water and/or hail resistance.

 

8.8  Attachment for Low-Slope Roof Systems.

 

8.8.1  Full Anchorage. For relatively inelastic roof membranes such as BUR and MB, solid adhesion helps restrain the roof membrane and uniformly distribute thermal stresses. When insulation is used, it is fastened or adhered to the deck. The membrane is fully adhered to the thermal insulation using hot asphalt or cold adhesive. Polyurethane foam is sprayed directly to the substrate, especially in re-cover of existing BUR thereby being fully adhered as well.

 

8.8.2  Partial Attachment. In partially attached systems the membrane is mechanically

anchored through the insulation into the deck, or in a few cases, partially adhered with strips or spots of adhesive. This is common with flexible single-ply roof membranes. Fasteners are typically placed in the seams area where by can be covered by the overlapping sheet.

 

8.8.3  Loose-Laid Attachment. For loose-laid systems the membrane is unattached to the substrate and is held in place by ballast. Restraint is required only at perimeters and curbs.  Loose-laid roofs are used with elastomeric (EPDM) and some thermoplastic (e.g., TPO) systems. These are very inexpensive roof systems if the structure can handle the ballast weight.

Caution:

In positive pressure buildings air barriers should be used with loose laid and partially attached membranes to avoid billowing and peeling.

 

8.9  Labor.

 

8.9.1  Highly Intensive: BUR, MB

 

8.9.2  Moderately Intensive: SSSMR—The system is very unforgiving of installation defects.

 

8.9.3  Medium Intensity: Fully adhered and mechanically fastened single-ply.

 

8.9.4  Low Intensity: Spray Foam requires the smallest crew (but is the most machine

intensive and weather sensitive).

 

8.10  Slope.

Some Typical Slope Limitations for Low-Slope Roof Systems

Table 12

 

9.  PRINCIPAL CONSIDERATIONS WHEN SPECIFYING STEEP-SLOPE (WATERSHEDDING) ROOFING. This category covers systems that range from asphalt shingles, wood shingles and shakes, clay and concrete tile, slate, and metal look-a-likes. Also included are architectural metal panels with a variety of seams (Figure 11). Slopes are generally 25% (3:12) or greater. Most must be continuously supported on a solid deck (e.g., plywood or oriented strand board [OSB]). However, some varieties (e.g., clay and concrete tiles) may be supported on spaced horizontal batten boards.  Underlayments such as roofing felt, self-adhering MB or plastic film are usually required over the entire roof to provide a secondary line of defense against driving rain and blowing snow. In cold regions, a completely sealed MB underlayment is needed along eaves, in valleys, and at dormers, skylights, chimneys and such to resist leaks from water ponded behind ice dams.

Architectural Metal Seams

Figure 11

 

9.1  Aesthetics. By their very nature steep roofing is highly visible. Appearance may be of primary concern to the designer. Regional preferences exist. For example, red tile roofing is very common and highly desirable in the Southwest, while light gray concrete tile is preferred in Florida. Wood shakes give a textured natural look preferred in the Pacific Northwest.

 

9.2  Labor Intensity and Labor Skill.

 

9.2.1  High Intensity. Heavy brittle units of clay, tile or slate.

 

9.2.2  Medium Intensity. Architectural metal, wood shakes.

 

9.2.3  Low Intensity. Shingles.

 

9.3  Watershedding. Steep roofs rely on gravity to cause water to flow away from headlaps.  Recommended minimum slopes are shown in Table 13. Lower slopes are sometime permissible by increasing overlap or enhancing the waterproofness of the underlayment.

Minimum Slopes for Typical Steep Roofing Systems

Table 13

 

9.3.1  Valleys and Eaves. Valleys must be well constructed. The slope of a valley will be less than that of the intersecting planes that form it. Exterior drainage over the roof edge or to a gutter is typical but may be troublesome in cold regions since ice dams may form there.

 

9.3.2  Underlayments. Sealed underlayments of self-adhering modified bitumen are typically used along the eaves to at least 24” beyond the interior wall line (Figure 12a) and as valley lining. Occasionally the entire roof deck is covered with such a membrane. Note that this can lead to problems if indoor moisture is not isolated from the roof by well made vapor and air barriers. Underlayments are used in steep roofing as a secondary defense against water penetration (Figure 12b). These include No. 15 felt, No. 30 felt, and self-adhering MB sheets. For hydrokinetic and crafted metal, self-adhering MB sheets are essential as a secondary water barrier.

Self-Adhesive Eaves Flashing

(Underlayment is sealed from eave to 24” within wall line.)

Figure 12a

Underlayment for Steep Roofing

(Underlay felt is unsealed)

Figure 12b

9.3.3  Energy Efficiency. Steep roofs generally cover an attic space (figure 2-13) (with the exception of cathedral ceilings). The floor of an attic can be inexpensively insulated with nonstructural insulations such as fiberglass batts, mineral wool, expanded vermiculite, or treated cellulose. Where the thickness of the insulation is not limited by clearance problems, very high thermal resistances (e.g., Rsi > 5.56, R > 30) can be achieved. If a vapor retarder is required for a cold arctic climate the retarder needs to be placed on the interior (warm side) of the insulation.  The attic space above this insulation should be ventilated to remove moisture and to keep the attic relatively cold; this minimizes ice damming at eaves.

Vented Attic Space

Figure 13

 

 

9.3.4  Durability. Mean durability of common steep roofing has been estimated in one survey as:

 

Mean Durability of Common Steep Roofing

Table 14

 

10.  ADDITIONAL CRITERIA AND DISCUSSION.

 

10.1  Wind. Maximum wind speeds associated with locality and storm type determine needed resistance. ANSI/ASCE 7-95 and EI01S010 provide design information.

 

10.1.1  Adhered Systems. Air impermeable roof decks such as poured concrete, with adhered or mechanically fastened insulation and fully adhered membranes, are highly wind resistant. Tests conducted by the Factory Mutual System have determined that BUR systems installed this way have resisted 8.6 kilopascals (180 psf).

 

10.1.2  Metal Panel Systems. Metal panels are generally rated by the Underwriters 580 procedure, with UL 90 ratings considered excellent. However, because some SSSMR panel systems with UL 90 ratings have failed in service, structural standing seam metal roof systems must pass the ASTM E1592 test method.

 

10.1.3   Ballasted Systems. Ballasted single-ply systems rely on heavier and larger ballast in more wind prone exposures. SPRI has developed wind guidelines in their ANSI-SPRI RP-4 document based upon ANSI/ASCE 7-95 guidelines. Higher parapets have a beneficial effect on ballasted systems. Above certain building heights, SPRI recommends against the use of ballast.

 

10.1.4  Mechanically Fastened Systems. Mechanically fastened single-ply systems use narrower starter sheets and increased fastener density in high wind areas. Examples of layout can be found in Factory Mutual Loss Prevention Data Sheet 1-29.

 

10.1.5  Foam Systems. Sprayed-in-Place Polyurethane Foam (SPF) systems have proven very wind resistant and are effective in protecting the structure against wind hurled missiles.

 

10.1.6  Problems with Small Roof Aggregate. Roofs adjacent to airport tarmac activities should avoid aggregate surfacing as loose aggregate may be blown off the roof and sucked into engines. Loose stone ballast which is much larger, is used successfully at many airports.

 

10.1.7  Wind Rated Roofs. Underwriters Laboratories lists wind rated systems in their Roofing Materials and Systems Directory as Class 30, 60 or 90. Factory Mutual Research Corporation lists wind rated systems in their Approval Guide with ratings ranging from 60 to 210 psf.

 

10.1.8  Steep Roofing. For most steep roofing systems, additional fastening is required for

high wind areas (e.g., six fasteners per asphalt shingle instead of four, addition of nose clips for tiles, etc.).

 

10.2  Ice and Hail. The formation of ice can cause the roof membrane to split. Ice can also affect roofing performance by scrubbing the membrane and eroding the surface. This can be especially detrimental to materials with a relatively high glass transition temperature (Tg).  Bituminous materials have a Tg of approximately 32°F. Modified bituminous materials with an SBS modifier can have a Tg as low as minus -30°F.  EPDM membranes report a Tg less than -40°F. The Tg of thermoplastics may increase with age (i.e., loss of plasticizer in PVC).  Ponding promotes ice damage; drainage avoids it.

 

10.2.1  Impact Damage. Falling ice, such as from overhead towers, causes impact damage.  Ballasted EPDM provides some protection. Protected membrane roofs in which both polystyrene insulation and ballast are placed over the finished roof membrane provide excellent impact resistance.

 

10.2.2  Perimeter Icing. Ice formation at eaves, scuppers, and gutters is a major design concern. For low-slope roofing selection of internal drainage where building heat keeps the drain lines unfrozen is recommended.

 

10.2.3 Minimizing Icing Problems. For metal and steep roofing heating cables are sometimes necessary but not especially reliable. In cold regions use of a cold roof in which the roof is ventilated to prevent formation of icicles and ice dams is preferred. Self-adhering waterproof membranes are needed to avoid leaks from ice damming (Figure 10).

 

10.2.4  Hail Damage. Weather maps are available that generally divide the U.S. into regions that require resistance to severe hail (2 in. dia.), moderate hail (1-1/2 in. dia.), and areas of low hail probability. Hail resistance is affected by the compressive strength of the substrate, thickness of the membrane, tensile strength, and age/brittleness of the material.

 

10.3  Snow. Snow removal operations in which shovels or snow blowers are used can cause severe damage especially to cold, brittle membranes. Smooth single-ply membranes and metal roofing are extremely slippery when wet or when a thin ice film covers melt water. Roof walkways consisting of compatible materials are essential when it is necessary to walk on wet or frozen roofs.

 

10.3.1  Metal Roofs. TI 809-52 recommends that SSSMRs should have a minimum slope of 8.3% in cold regions.

 

10.3.2  Snow Loads. Snow load information is available in ANSI/ASCE 7-95, TI 809-01, and TI 809-52.

 

10.4  Slope. Drainage is essential on all roofing systems. For hydrokinetic roofing the drainage must be positive and rapid. Shingles, tiles, and the like, generally have industry minimum recommended slopes of 33% to 42%. Sometimes a lower slope option is available if waterproof underlayments are used.

 

10.4.1  Metal Roofs. Minimum slopes for metal roofs vary from 4% to 33%, depending upon roof type.

 

10.4.2  Membrane Slope. Low-slope membranes should also comply with a minimum slope of 2% (1/4 in./ft.). Where ponding is unavoidable such as in spray ponds, a BUR with double poured aggregate and bitumen is sometimes used. Coal tar pitch membranes are used at slopes as low as dead level and to a maximum slope of 2% (1/4 in/ft.). drainage is also needed. However, small puddles are inevitable as SPF is never completely smooth. Small puddles should dry out within 24-48 hours after inclement weather.  Additional elastomeric coating is recommended where ponding is anticipated.

 

10.4.3  Foam Slope. For Sprayed-in-Place Polyurethane Foam (SPF) systems positive drainage is also needed. However, small puddles are inevitable as SPF is never completely smooth. Small puddles should dry out within 24-48 hours after inclement weather. Additional elastomeric coating is recommended where ponding is anticipated.

 

10.4.4  Reroofing. In reroofing and re-covering applications, correcting the slope to 2% (1/4 in./ft.) is sometimes unfeasible because of low windows, flashings, etc. In these cases, tapered insulation at 1.5% (3/16 in./ft.) slope may be an acceptable compromise.

 

10.4.5  Steep Roof Conversion. Conversion of a poorly draining roof to a steep roofing system may be accomplished on a relatively narrow roof system building by installing new sloped joists.

 

10.5  Vapor, Humidity, Moisture and Condensation. Moisture can be carried through materials by diffusion or by the movement of air. Air barriers are needed to reduce air movement. They can be located anywhere within the building envelope. Vapor retarders, when needed, must be placed within the warm portion of the thermal insulation.

 

10.5.1 Self-Drying Systems. In cold weather, warm moist indoor air driven from within the building towards the colder exterior may accumulate during the winter then dry back out again during the summer months. Guidelines for the use of vapor retarders in roofs are presented in CRREL Misc. Paper 2489, Vapor Retarders for Membrane Roofing Systems.  Figure 14a indicates suggested maximum allowable relative humidities where summer dry-out should be adequate. Figure 14b is used to adjust Figure 14a for temperatures other than 60^oF.

 

10.5.2  Reverse Vapor Drive. For hot humid climates a reverse vapor drive may occur especially in cooler and freezer buildings. In this case the membrane and wall retarder sealed and continuous. Roof vents and breathing edge details must be avoided. For freezer buildings, consider separating the roof system from the freezer.

 

10.5.3  High Humidity Occupancies. For buildings with high interior relative humidity including bakeries, laundries, pools, kitchens, dining halls with serving lines and the like, vapor retarders are considered essential.

Interior Relative Humidities (%) with Interior Temperature of 68^oF)

Figure 14a

Temperature Conversion When Temperatures Differ from 68^o F

Figure 14b

Typical Indoor Relative Humidity in Winter

Table 15

 

10.5.4  Bituminous Vapor Retarders. Bituminous retarders are installed over solid fire barrier substrates such as concrete, gypsum board, or a fire resistant insulation. Bituminous retarders have near zero perm ratings. For most membrane roofing systems vapor retarder permeance should be below 0.5 perms (28.6 ng/s•sq m•Pa). Perm ratings for various vapor retarder materials can be found in the ASHRAE Handbook of Fundamentals as well as in industry literature.

 

10.5.5  Non-bituminous Vapor Retarders. Non-bituminous single-ply systems may use plastic films as vapor retarders. These can be successful if the seams and penetrations are carefully sealed with tape. Puncturing the retarder, either accidentally or by installing mechanical fasteners lessens its resistance to moisture.

 

10.5.6  PMRs. Protected Membrane Roofing systems (PMR’s) are very effective against vapor drive from within the building. The roof membrane itself serves as the vapor retarder as most, if not all, of the thermal insulation is located above it. Self-drying of the insulation (extruded polystyrene) to the atmosphere maintains the thermal resistance.

 

10.5.7  SPF Systems. SPF systems are commonly installed on re-cover installations where

the old bituminous membrane can be sealed to form a retarder. Dew point calculations are necessary to insure the dew point is within the upper SPF layer.

 

10.5.8  Steep Roofing. In steep roofing systems the retarder is usually a plastic film (poly), treated kraft paper or foil facing on batt insulation installed with the retarder facing the interior.  When an attic or cathedral ceiling is present, ventilation of the space above the insulation is essential since retarders are rarely completely sealed and some moisture accumulation would otherwise occur. Most codes recommend at least 1:150 net free ventilation area (total at eave and ridge) when a retarder is not installed to 1:300 when a retarder is in place. In cathedral ceiling construction larger net free areas are needed since friction losses in the narrow airway reduce ventilation.

 

10.5.9  Metal Systems. In structural metal systems where draped batt insulation is

used, it is difficult to completely seal the retarder facer even if tape is used. When high interior vapor conditions exist the use of a subdeck to support a retarder film may be necessary. Other roofing systems should also be considered as such systems are not good at resisting high internal relative humidities.

 

10.6  Considerations When Using Thermal Insulation. Thermal insulation is important in modern buildings both for energy conservation and human comfort and may impact roof membrane performance.

 

10.6.1  Thermal Resistance. Resistance to heat flow through the entire roof structure (characterized by the R factor) should be as high as is both practicable and cost effective. In general an R factor of > 20 (Rsi > 3.57) is recommended. Note: U = 1/R

therefore, the U factor should be < 0.05 Btu/hr•ft2 ^oF.

Unit Resistances (i.e., Resistivity) of Common Roof Insulations

Table 16

 

10.6.2  Installation Locations. Thermal insulation may be installed in four locations.

 

10.6.2.1  Underdeck insulation (Figure 15).

 

• Wood frame structures with steep roofing often utilize batt insulation placed between the rafters. Vapor retarders of foil, kraft, or plastic film are located on the inside face of the insulation. With structural standing seam metal systems, batts are draped over the purlins. In attics, the insulation is usually positioned between ceiling joists.

 

• An advantage of underdeck insulation is that inexpensive nonstructural insulations such as batts may be used.

 

Under Deck Insulation

Figure 2-15

 

• A disadvantage is that the roof deck suffers greater thermal stress than when it is overlaid with insulation. Another disadvantage is that it is difficult to vapor seal such construction and make it resist air exfiltration and as a result moisture problems are prone to occur. Ventilation is usually required but ventilating low-slope framed roofs lacking tight air barriers is apt to increase moisture problems, not eliminate them.

 

• Common underdeck materials include compressible batts of glass fiber and mineral wool. Thermal spacers of rigid plastic foam are placed over the purlins of SSSMR systems to maintain the thermal resistance where the batts are compressed.

 

10.6.2.2  Self-insulating roof deck (Figure 16):

Self-Insulating Roof Deck

Figure 16

 

• Insulating decks such as structural wood fiber are less popular today because it is difficult to achieve high R values within the deck itself. In reroofing situations supplemental insulation would often be added on top of such a deck. In some new assemblies a composite of structural wood fiber topped with plastic foam is used. The underside of these self-insulating decks can be exposed to the interior and serves as an attractive acoustical ceiling.

 

10.6.2.3  Thermal insulation within the roofing sandwich (Figure 9).

 

• Insulation on top of the roof deck is the most common configuration for membrane roofing. For adhered membrane systems the thermal insulation restrains the membrane against wind loss or shrinkage and must have adequate structural strength. For mechanically anchored and ballasted systems compressive strength and stability are important. If hot asphalt or solvents are used in construction of the membrane, the insulation must resist degradation by these agents.

 

• Common materials for adhered systems include faced polyisocyanurate foam

(ASTM C1289), perlite (ASTM C728), rigid glass fiber boards (ASTM C726), wood fiber (ASTM C208), and cellular glass (ASTM C552). Verify that the combination of membrane and roof insulation/facer are Fire and Wind Rated.

 

• For mechanically fastened and ballasted systems expanded and extruded polystyrene (ASTM C578) are added to the above list. (They could melt or dissolve if placed in contact with hot bitumen or solvent-based adhesives).

 

• Some decay of R value is observed with HCFC blown foams (urethanes and

isoboards) due to diffusion of air and moisture into the cells of the foam. Manufacturers publish aged R values to reflect this decay. Always used aged R-values for these materials. Since diffusion starts at the surface of the foam, thicker foams are more thermally stable.

 

• Wood fiber boards should be manufactured to use as roof insulation (meeting

ASTM C208), not sheathing boards, and should be limited to 4 ft. in length and width.

 

• When mechanical fasteners are used to secure thermal insulation, it is recommended that the nail-one, mop-one technique be used. This minimizes a thermal bridging and avoids nail-popping of the membrane. When multiple layers of insulation are used, vertical joints should be offset to reduce heat losses. Straight-through joints can take away 10% of a roof’s insulating ability.

 

10.6.2.4  Protected membrane systems (Figure 17).

 

• In PMR systems only extruded polystyrene is suitable in the sometimes wet environment above the completed roof membrane. This insulation protects the membrane from thermal stress and abuse.

 

• Ballast and filter fabric is needed to hold the loose-laid insulation in place.

 

Protected Roof Membrane System (PMR)

Figure 17

 

10.7  Energy and Solar Radiation. The ratio of roof area on a low-rise commercial building is high relative to wall area. Such roofs can provide a great opportunity for energy conservation.  This can be accomplished by using well insulated, high thermal mass structures to reduce summer cooling loads, garden roofs, or high albedo roof coatings.

 

10.7.1  Heat Gain. For roofs in hot or temperate climates, light colored roof surfaces reduce heat gain. For membrane roof systems, light colored aggregate (gravel surfaced roofs) or mineral granules (capsheets [ASTM D249, D371, D3909] and MB capsheets [ASTM D6162, D6163, D6164, D6222, D6223]) will reduce heat maximum surface temperatures by up to 35°F over black membranes. Aluminum coatings (ASTM D2824) are approximately the same, while white coatings (ASTM D6083) have been observed to reduce temperatures by more than 45°F (provided that the roof stays clean). The use of pavers and heavy ballast reduce heat gain through thermal lag; that is, the high heat capacity stores some of the gained heat delaying the startup of the building’s air conditioning system. The ASHRAE Handbook of Fundamentals uses the term Equivalent Temperature Difference (ETD) in energy calculations. The smaller the ETD, the better the system is at reducing peak solar loads.

 

 

Equivalent Temperature Difference

Table 2-17

 

reflective roof surfacing materials (e.g., white granules on shingles). Radiant barriers (reflective foils) placed in attics are also effective.

 

10.8  Fire Considerations.

 

10.8.1  Topside Fire Ratings. Because of its large surface area, roofing plays an important role in fire protection. Fire hazards can be defined as:

 

10.8.1.1  External, where the source is outside the building such as from wind blown flaming debris. Tests for external fire resistance are referred to in building codes as Class A, B and C.

 

• An external fire rating is established by constructing and testing roofing assemblies by methods described in ASTM procedure E108 (also known as UL790). In this method relative degrees of fire resistance are established.

 

o   Class A roof coverings are effective against severe fire exposures. Under such exposures roof coverings of this class are not readily flammable and do not carry or communicate fire; afford a fairly high degree of fire protection to the roof deck; do not slip from position; possess no flying brand hazard; and, do not require frequent repairs in order to maintain their fire-resistant properties.

 

o   Class B roof coverings are effective against moderate fire exposures.  Under such exposures roof coverings of this class are not readily flammable and do not readily carry or communicate fire; afford a moderate degree of fire protection to the roof deck; do not slip from position; possess no flying brand hazard; but, may require infrequent repairs in order to maintain their fire-resistant properties.

 

o   Class C roof coverings are effective against light fire exposures. Under such exposures roof coverings of this class are not readily flammable and do not readily carry or communicate fire; afford some degree of fire protection to the roof deck; do not slip from position; possess no flying brand hazard; and, may require occasional repairs or renewals in order to maintain their fire-resistant properties.

 

• Class A does not mean Grade A!  Note: In this classification only fire performance is considered. A specifier should select the degree of fire resistance required but recognize that selecting a higher rating does not assure better waterproofing nor longer life. In fact, some compromise in durability may have been made to meet the higher fire rating.

 

• ASTM E108 fire tests may be conducted on steep roofing, membrane roofing, SPF, and metal panels. Listings of systems that meet these requirements are found in the Underwriters Laboratories Roofing Materials and Systems Directory, the Factory Mutual
• Approval Guide, and reports/directories published by several other qualified testing agencies.

 

• Qualified listings:

 

o   If a roofing assembly fails to meet burn-through requirements of ASTM

E108 it may still be listed for use with non-combustible decks such as steel, concrete, and gypsum.

 

o   Roofing assemblies are listed at the maximum incline to which the rating applies. As long as the structure under consideration is at a lower or equal incline to that listed it complies with the fire rating.

 

o   If a listing is intended for use as a roof superimposed over an existing roof, it should be listed in the UL Roofing Materials and Systems Directory under the category Maintenance and Repair Systems. In the FM Approval Guide it will be listed as a Re-cover.

 

o   In general, only the materials listed qualify and only when used in the manner described in the directories. Additional insulation, for example, might worsen the flame spread.

 

10.8.1.2  An internal (underdeck) fire is when the flame spread is underneath the roof

deck. Listings are referred to by the Approval Rating, usually Factory Mutual Class 1 or

Underwriters Laboratories Insulated Metal Deck or Non-metallic Decks Constructions.

 

• Background—In 1953, a large insulated steel roof deck building suffered an unexpected, catastrophic fire loss due to an underdeck fire exposure. The roofing components above the deck contributed fuel to spread the fire. Tests conducted on full scale test buildings confirmed the hazard. In the late 1950’s, laboratory tests were established and correlated to the full scale data. Factory Mutual uses a calorimeter to establish fire performance while Underwriters Laboratories uses a modified Steiner Tunnel test. Successful systems are listed by FM as Class 1 while Underwriters lists them as either Rated Metal Deck or Rated Non-Metallic Assemblies.

 

• The underdeck ratings do not assure zero risk. The ratings assume an acceptable risk assuming normal fire detection and fire control procedures are available. If an insulated steel deck system fails to comply with the requirements of FM Class 1, it is designated Class 2. Class 2 constructions may be converted to Class 1 by the addition of underdeck fireproofing. Class 2 constructions may also be acceptable if an approved sprinkler system is used.

 

• Fire endurance tests. These are time-temperature tests (ASTM E119) in which the roof-ceiling assembly is subjected to a rising heat load until either the interior structural elements yield, or the temperature on the exterior roof system reaches 139oC (250oF) above the ambient.

 

o   The minimum elapsed time required before the end point is reached is

usually established by building code or occupancy (e.g., 1-hour, 1-1/2 hour, etc.).

 

o   Rated assemblies are listed by UL in their Fire Resistance Directory and by FM in their Approval Guide. Other testing agencies list rated assemblies in their directories as well.

 

·         Assure that fire compliance (ratings) pertain to the entire assembly. Each component of the system must be listed in the above directories. Materials delivered to the job site should bear labels indicating compliance with the construction intended. The label also provides third party assurance that the products delivered to the construction site are essentially unchanged from those tested and listed.

 

10.9  Seismic Requirements. While membrane roofing materials in general do not affect seismic stability of a structure, components of the roof system may be important. Roof decks, for example, usually serve as a diaphragm increasing lateral stability.

 

10.9.1  Bracing for SSSMRs. Structural metal systems with floating clips require bracing since the structural standing seam metal panels do not provide diaphragm action. An alternative to bracing is to use a steel subdeck to serve as the shear diaphragm.

 

10.9.2  Inertia Effect. Heavy roofing materials such as ballast or pavers may result in an inertia effect that should be included in the design. This may be beneficial or detrimental.

 

10.9.3  Lateral Motion of Tiles. In steep roofing, seismic motion may shatter materials such as cement and clay tile. Correct use of mechanical anchors may prevent damage. Twisted wire systems are recommended for earthquake zones. The National Tile Roofing Manufacturers Association requires two nails or a nail and a clip on every tile to resist seismic damage.

 

10.9.4  Restraining Roof Tiles. IR-32-1 (9/89), a Title 24 California code addresses the attachment of tile, and allows the combination of wire tie and nose clips (wind locks or tile locks). Nails or wire ties are to be copper, brass, or stainless steel 11 ga. minimum with two per tile.  Nails are to penetrate roof sheathing, battens, or support members 3/4 in. min. Ring shanked nails may be used when sheathing thickness is less than 3/4 in.

 

10.9.5  Parapet Walls. Parapet walls must be used with care. Through-wall flashings or

cut reglets must be avoided as they reduce the wall’s resistance to lateral forces.

 

10.9.6  Roofing Over Seismic Straps. Seismic straps (heavy metal plates) are sometimes installed over plywood roof decks and between decks and walls. Where roof insulation is not used (i.e., west coast capsheet construction), use construction details provided by the Western States Roofing Contractors Association on how to roof over the straps (Figure 18).

Roofing Over Thick Seismic Strap

Figure 18

 

10.10  Adequate Design Details. Complete sectional views of every location where the roof changes plane or there is a roof penetration or attachment should be provided on contract drawings. Sections and design details should be drawn to a legible scale with each element of the roofing system identified.

 

CHAPTER 2

COATINGS AND PAINTS

 

1.  SELECTION OF COATINGS

 

1.1 Selection Criteria. The best selection of a coating system for a particular service is determined by a variety of factors. These include desired properties, work requirements and

limitations, safety and environmental restrictions, compatibilities, and costs.

 

1.1.1 Desired Film Properties. In selecting a coating system, the first consideration is the desired properties of the system for the particular service. Desired properties may include one or more of the following aspects:

 

• Resistance to exterior weathering (chalking; color and gloss retention)
• Water, fuel, or chemical resistance
• Abrasion, heat or mildew resistance
• Appearance (color, gloss, and texture)
• Drying time
• Ease of application and maintenance

 

1.1.2 Work Requirements or Limitations. The following work requirements or limitations may have to be considered:

 

• Type of surface preparation
• Access to work
• Drying times
• Necessary applicator skills
• Necessary equipment
• Scaffolding for access to work

 

1.1.3 Safety and Environmental Restrictions. It will be necessary to conform to all prevailing safety and environmental regulations concerning materials and processes to be used for surface preparation and for coating application.

 

1.1.4 Compatibilities. Coating systems must be compatible with the surfaces to which they are applied. Coating incompatibility can cause failures at or just after application or after a much longer time. Failures occurring just after application are due to solvent incompatibility or wetting problems. Failures associated with slow chemical reactions, such as those occurring between alkaline surfaces (e.g., concrete and galvanized steel) and oil-based paints or mechanical property mismatches (e.g., a rigid coating applied over a more flexible one) cause failure in a longer timeframe. The failure more often is peeling. For existing coatings being repainted, compatibility generally means that topcoats should be of the same generic type or curing mechanism as undercoats. One exception to this rule is inorganic zinc coatings. Since inorganic zinc coatings frequently do not bond well to themselves, it is safest to repair them with zinc-rich organic coatings.  A simple test to classify coatings is to determine solvent sensitivity using an methylethyl ketone (MEK) or acetone rub test. To do this, soak a cloth in MEK or acetone, rub it against the existing paint, and visually check for pick up of  paint. The paint is classified as "solvent soluble" if paint is picked up, and as "solvent insoluble" if not.  Another practical method of ensuring topcoat solvent compatibility is to coat a small test area of the existing coating with the paint selected for the work. If situations permit, this test is preferred over the MEK rub test because it is specific for the surface to be repainted. The test area should be visually inspected the following day (or preferably after 3 or more days) for bleeding of undercoat, wrinkling, loss of adhesion, or other coating defects. Although most incompatibility problems are apparent in a couple of days, some types of incompatibility may not become apparent for several months or until after a change of seasons. These types are usually associated with mechanical film properties.

 

1.1.5 Costs. Life cycle cost has always been one of the most important considerations in selection of coating systems. Life cycle costs include original surface preparation, materials, and application and necessary maintenance throughout the life of the coating system. Today, the expense of containment of old paint during its removal and disposal of debris that is often

considered to constitute hazardous waste must be included. This usually means that the system with the maximum maintainable life is the best choice.

 

1.2 Specifications for Lead- and Chromate-Free Coatings with VOC Limits. The coating specifications listed below in Table 1 are lead- and chromate-free and have limitations on their contents of VOC.

 

 

Table 1

Lead- and Chromate-Free Coating Specifications With VOC Limits

Latex Coatings
Listed latex coatings are available with a VOC content of no more than 250 grams per liter unless otherwise specified
TT-P-19	Exterior acrylic emulsion coating, available in a wide variety of colors and flat gloss finishes
TT-P-29	Interior latex paint, flat, available in white and tints
TT-P-650	Interior latex primer coating for gypsum board or plaster
TT-P-1510	Latex exterior flat finish coating, available in a variety of colors
TT-P-1511	Latex interior coating, available in gloss and semigloss in white and tints
TT-P-1728	Latex, interior, flat, deep-tone coating
TT-P-001984	Primer, latex, for wood
TT-P-002119	Latex high-traffic coating, available in flat and eggshell and a variety of colors
TT-E-2784	Acrylic emulsion exterior enamel, gloss and semigloss, available in a wide variety of colors
MIL-E-24763	Acrylic water-emulsion coating intended for shipboard use, available in 275 and 340 grams per liter VOC classes; high, medium, low, and flat glosses; and a limited number of colors
MIL-P-28577	Corrosion-resistant latex primer for metals
Stains
MIL-P-28578	Waterborne acrylic semigloss finish, available in a wide variety of colors
TT-S-001992	Exterior latex stain, semi-transparent and opaque, available in a variety of colors
Clear Floor Finishes
A variety of clear floor finishes are available from the Maple Flooring Manufacturers Association (MFMA) specifications, Heavy-Duty and Gymnasium Finishes for Maple, Beech, and Birch Floors. Suppliers must be contacted to determine VOC content.

 

Table 1 (continued)

Lead- and Chromate-Free Coating Specifications With VOC Limits

 

Oil and Alkyd Coatings
SSPC PAINT-25	Corrosion-resistant raw linseed oil and alkyd primer, usually available at 300 grams per liter VOC but no requirement listed
TT-P-25	Oil-based primer for wood, normally available with a VOC content less than 350 grams per liter
TT-P-31	Red and brown oil ("roof and barn") paint, usually available with 250 grams per liter VOC content but no requirement specified
TT-E-489	Alkyd enamel, with 420 grams per liter VOC limitation, available only in gloss, but in a wide variety of colors
TT-P-645	Corrosion-resistant alkyd primer, with a 340 VOC limitation
TT-P-664	Corrosion-inhibiting alkyd quick-dry primer, with a 420 grams per liter VOC limitation
MIL-E-24635	Silicone alkyd enamel, available in limited colors, 275, 340, and 420 grams per liter VOC types, and high, medium, low, and flat gloss classes
MIL-P-28582	Alkyd primer normally available at less than 350 grams per liter

 

 

 

Table 1 (continued)

Lead- and Chromate-Free Coating Specifications With VOC Limits

Epoxy Coatings
MIL-P-24441	Epoxy-polyamide, two- and three-coat systems, available in types with 340 VOC and limited colors
MIL-P-53022	Fast-dry epoxy primer with 420 grams per liter maximum VOC content
MIL-P-85582	Waterborne epoxy primer with 340 grams per liter maximum VOC content
Textured Coatings
TT-C-555	Waterborne or oil- or rubber-based textured coating available at 250 grams per liter
Urethane Coatings
MIL-C-85285	High-solids aliphatic urethane coating, with 340 and 420 grams per liter VOC types, available in a variety of colors and in glass and semigloss
Zinc-Rich Coatings
MIL-P-24648	Zinc-rich coating, aqueous and organic solvent types, self-curing and post-curing classes, organic and inorganic

 

 

1.3 Recommendations for Different Substrates. This discussion provides general recommendations for wood, concrete and masonry, steel, galvanized steel, and aluminum surfaces. The recommended dry film thickness (dft) in mils is provided for coating specification recommended for a particular substrate.  Referenced standards for coatings

provide for lead- and chromate-free products that are low in VOCs. Although such requirements may not be necessary at all projects currently, such requirements may occur in the near future.

 

In making local repairs of damaged coatings, loose paint should be removed by scraping with a putty knife before lightly sanding or abrasive blasting any exposed substrate and feather-edging existing sound paint to obtain a smooth transition with the repaired area. Coats of repair material should be extended 1 inch onto the surrounding sound coating.

 

1.3.1 Recommendations for Wood. Oil-based and waterborne coatings and stains (frequently called latex) perform quite well on new wood. A two-coat system, paint or stain, is normally applied. However, as additional coats are applied to resurface or repair weathered paint, the film thickness may become sufficient to reduce the total flexibility to the point that

results in disbonding of the total paint system from the surface.  Thus, when topcoating or making localized repairs, no more coating should be applied than necessary to accomplish the desired goal.

 

Surface preparation of new wood normally consists of lightly hand sanding or power sanding, carefully controlled so that it does not damage the wood. Sanding is also appropriate for preparing weathered surfaces for refinishing and for spot repairing areas of localized damage.

 

1.3.1.1 Oil-Based Paints. Historically, wood has been successfully painted with oil-based products that penetrate the surface well. These coatings are very easy to apply.

 

Oil-Based Paint System for Wood
Surface Preparation	Primer	Topcoat
Sand	one coat TT-P-25 or MIL-P-28582, 2  mils dft,	one-two coats MIL-E-24635 or TT-P-102, 2 mils dft per coat

 

1.3.1.2 Water-Emulsion Paints. More recently, latex coatings have been found to be very effective in providing attractive, protective finishes. They are also less affected by moisture

than are oil-based finishes and are generally more flexible and thus less susceptible to cracking as the wood swells and contracts with moisture changes.  A problem sometimes arises when repairing or topcoating existing smooth alkyd coatings with latex paints. To obtain good intercoat adhesion, it may be necessary to lightly sand the existing paint and/or apply a surface conditioner containing tung oil or some other oil that wets surfaces well before applying the first coat of latex paint.

 

Waterborne Paint System for Wood
Surface Preparation	Primer	Topcoat
Sand	One coat TT-P-001984, 1.5 mils dft	One-two coats TT-E-2784 or other appropriate latex paint in Table 1, 1.5 mils dft per coat

 

 

1.3.1.3 Semi-Transparent Stains. Because oil-based and waterborne paints form continuous films, they may form blisters or disbond because of moisture in the wood attempting to escape.  Semi-transparent stains do not form continuous films on wood and so do not have this problem. Thus, they are a good alternative on new wood. Additional coats applied over the years or heavybodied stains will, however, form continuous films.

Stains for Wood
Surface Preparation	Primer	Topcoat
Sand	One coat TT-S-001992, 1.5 mils dft	One coat TT-S-001992, 1.5 mils dft

 

 

1.3.1.4 Clear Floor Finishes. A variety of clear floor finishes are available from MFMA Heavy-Duty and Gymnasium Finishes for Maple, Beech, and Birch Floors. Suppliers on the attached list must be contacted to determine VOC content. 

 

1.3.2 Recommendations for Concrete and Masonry Surfaces.  Concrete and masonry surfaces, as well as those of stucco, plaster, wallboard, and brick, can be coated with a variety of systems depending upon the desired purpose and appearance.  Surface preparation is usually accomplished by power washing with aqueous detergent solution to remove dirt and other loose materials. Any oil or grease will have to be removed by solvent or steam cleaning; any mildew, by scrubbing with bleach; and any efflorescence or laitance, by brushing, followed by acid treatment.

 

1.3.2.1 Waterborne Coatings. A two-coat waterborne (latex) system provides an attractive breathing film that is normally less affected by moisture in the concrete than non-breathing systems. The latex material is a self-primer in this service, unless otherwise stated. Alkyd and other oil-based coatings should not be applied directly to concrete or masonry surfaces, because the alkalinity in the concrete will hydrolyze the oil in the binder and cause the coating to peel. However, they can be applied over concrete or masonry surfaces primed with waterborne coatings to produce a tougher, more washable finish.

1.3.2.2 Elastomeric Coatings. Elastomeric, waterborne acrylic coating systems also perform well to seal and protect concrete/masonry surfaces and are normally very low in VOCs.  They can successfully bridge fine or larger caulked cracks.  There are no federal specifications for them.

 

Elastomeric Waterborne Acrylic System for Concrete or Masonry
Surface Preparation	Primer	Topcoat
Power wash	One coat primer recommended by supplier of elastomeric coating, dft varies with supplier	One coat elastomeric acrylic coating, 10 -20 mils dft

 

1.3.2.3 Textured Coatings. Textured coatings system can bridge fine cracks and waterproof from wind-driven rain. They are normally applied over a primer recommended by the supplier to insure good adhesion. They are available in a variety of textures and may be waterborne or oil or rubber-based products with a VOC limit of 250 grams per liter.

 

Textured Coating System for Concrete or Masonry
Surface Preparation	Primer	Topcoat
Power wash	One coat primer recommended by supplier of textured coating, dft varies with supplier	One coat TT-C-555, 20 – 30 mils dft

 

1.3.2.4 Epoxy Coatings. A two-coat epoxy system will seal and protect concrete/masonry surfaces well. An aliphatic urethane finish coat should be used rather than the second epoxy coat on exterior surfaces to improve the weatherability.

 

 

 

Exterior Epoxy/Urethane System for Concrete or Masonry
Surface Preparation	Primer	Topcoat
Power wash	One coat MIL-P-24441 Formula 15, 3 mils dft	MIL-C-85285, Type II, 2 mils dft

 

 

Interior Epoxy System for Concrete or Masonry
Surface Preparation	Primer	Topcoat
Power wash	One coat MIL-P-24441, Formula 150, 3 mils dft	One coat MIL-P-24441, of another color, 2 mils dft

 

1.3.3  Recommendations for Steel. Presently, a high-performance coating system is recommended to prolong the service before it becomes necessary to remove and replace it. Costs in coating removal, especially where there are restrictions on abrasive blasting, are very high.  Abrasive blasting is always preferred to alternative methods of preparing steel surfaces for painting. It cleans the steel and provides a textured surface to promote good primer adhesion. A commercial blast specified by the Steel Structures Painting Council [re-named the Society for Protective Coatings in 1997] (SSPC) is (SSPC SP 6) is normally adequate for alkyd and epoxy primers for a moderate environment. A near-white blast (SSPC SP 10) is required for epoxies, including zinc-rich epoxies, exposed to a severe environment such as marine atmospheric or water or fuel immersion. Some manufacturers may specify a white metal blast (SSPC SP 5) for particular coatings for special applications. It is important that a contract specification does not conflict with the coating manufacturer's written directions. A white metal blast (SSPC SP 5) is recommended for zinc-rich inorganic primers. If abrasive blasting cannot be done, then power tool cleaning to bare metal (SSPC SP 11) is recommended. It provides a surface cleanliness and texture comparable to those of a commercial blast (SSPC SP 6). Hand tool cleaning (SSPC SP 2) or power tool cleaning, however, may be adequate in making localized repairs.

 

1.3.3.1 Alkyd Systems. In the past, many steel structures with atmospheric exposures were coated with an alkyd or other oil-based system. Three-coat alkyd systems provided adequate protection in moderate atmospheric service. On new painting, they are being replaced in significant part by epoxy systems that provide longer protection. Alkyd systems, however, will still be used in large volume for repairing old deteriorated alkyd systems.

Alkyd Coating System for Steel
Surface Preparation	Primer	Topcoat
SSPC SP 6	one coat TT-P-645 or SSPC PAINT 25, 2 mils dft	MIL-E-24635 or TT-E-489, 2 mils dft

 

1.3.3.2 Epoxy Coating Systems. A three-coat epoxy system provides good interior service in harsh as well as moderate environments. An aliphatic urethane finish system is used in

place of the third epoxy coat in exterior service to provide greater resistance to deterioration by ultraviolet light.  Several different epoxy mastic systems, some aluminum-filled,have

been used successfully on steel structures. However, there is no specification for one at this time.

 

Epoxy System for Exterior Steel
Surface Preparation	Primer/Mid Coat	Topcoat
SSPC SP 6 or 10	One coat each MIL-P-24441, Formulas 150 and 151, 3 mils dft	One coat MIL-C-85285, Type II, 2 mils dft

 

 

Epoxy System for Interior Steel
Surface Preparation	Primer/Mid Coat	Topcoat
SSPC SP 6 or 10	One coat each MIL-P-24441, Formulas 150 and 151, 3 mils dft per coat	One coat MIL-P-24441 of desired color, 3 mils dft

 

 

1.3.3.3 Zinc-Rich Coatings. Good protection from corrosion and abrasion can be provided by zinc-rich inorganic coatings. They perform well un-topcoated in a variety of environments except acidic or alkaline. They may be topcoated with an acrylic latex finish coat to provide a variety of color finishes. Epoxy (for interior) or epoxy and aliphatic urethane (for exterior)

topcoats may also be used. Localized repair of inorganic zinc systems is usually accomplished with a zinc-rich organic coating to permit good bonding to any exposed steel, inorganic coating, or organic topcoats.

 

Zinc-Rich System for Steel
Surface Preparation	Primer	Topcoat
SSPC SP 1	MIL-P-2468, Composition B (inorganic), 3 mils dft.  Composition A (organic) can be used when a more “forgiving” system is needed.	None, or one or more coats of acrylic or latex, epoxy, etc.

 

1.3.4 Recommendations for Galvanized Steel. Galvanized steel corrodes very slowly in moderate environments but may be painted with organic coating systems to provide color or additional corrosion protection, particularly in severe environments. It should never be coated directly with an alkyd paint, because the alkalinity on the surface of the galvanizing will hydrolyze the oil in the binder, degrading the binder, and cause paint peeling.  New galvanizing should be solvent or steam cleaned (SSPC SP 1, Solvent Cleaning) to remove any grease or oil before coating. Older, un-topcoated galvanizing should be power washed to remove any dirt or loose zinc corrosion products. Any loose coatings should also be removed by power washing or scraping and sanding to produce a clean, sound surface. Rust should be removed by waterblasting or careful abrasive blasting to limit the removal of galvanizing.

 

1.3.4.1 Epoxy Systems. Two coats of epoxy will provide long-term protection to galvanizing in interior service, as will one coat of epoxy and one coat of aliphatic urethane to galvanizing in exterior service.

 

 

 

Epoxy Coating System for Exterior Galvanizing
Surface Preparation	Primer	Topcoat
SSPC SP 1	One coat MIL-P-24441, Formula 150, 3 mils dft	One coat MIL-C-85285, Type II, 2 mils dft

 

 

Epoxy Coating System for Interior Galvanizing
Surface Preparation	Primer	Topcoat
SSPC SP 1	One coat MIL-P-24441, Formula 150, 3 mils dft	One coat MIL-P-24441 of desired color, 3 mils ft

 

1.3.4.2  Waterborne System for Galvanizing. Two coats of latex paint will provide a pleasing appearance and good protection to galvanized steel in moderate environments. They are easy to apply.

 

Waterborne Coating System for Galvanizing in Moderate Environment
Surface Preparation	Primer	Topcoat
SSPC SP 1	One coat TT-E-2784, 1,5 mils dft	One coat T-E-2784* (* other commercially available acrylic latex systems will also perform well)

 

 

1.3.5 Recommendations for Aluminum. Aluminum surfaces corrode very slowly in moderate environments. They may be coated to provide color or additional protection, particularly in severe environments. Epoxy and epoxy/urethane systems perform well in interior or exterior service, respectively. Alkyd systems usually require surface pretreatments containing toxic materials.  Because aluminum surfaces are relatively soft, they should not be cleaned by blasting with conventional abrasives or grinding to avoid damage. Any grease or oil should be removed by solvent or steam cleaning (SSPC SP 1). Dirt and other loose contaminants should be removed by power washing. Existing coatings are best removed by careful blasting with a soft abrasive (e.g., plastic). Alkaline strippers should never be used, because they will attack the aluminum.

 

 

Coating System or Aluminum
Surface Preparation	Primer	Topcoat
See above	MIL-P-24441, Formula 150, or MIL-P-53022, 3 mils dft	One-two coats MIL-C-85285, Type 2, 2 mils dft per coat

 

 

2.  SURFACE PREPARATION

 

2.1 Introduction. Surface preparation is the single most important factor in determining coating durability. Available data and experience indicate that in most situations, money spent

for a clean, well-prepared surface reduces life-cycle costs. A proper surface preparation:

 

• Removes surface contaminants (e.g., salts and chalk) and deteriorated substrate surface layers (e.g., rust and sunlight-degraded wood) which hinder coating adhesion and;

 

• Produces a surface profile (texture) that promotes tight adhesion of the primer to the substrate.

 

2.1.1 Selection Factors. Factors which should be considered in selecting the general type and degree of surface preparation are:

 

• Type of the substrate
• Condition of the surface to be painted
• Type of exposure
• Desired life of the structure, as some procedures are much more expensive than others
• Coating to be applied
• Environmental, time, and economical constraints

 

2.1.2 Specification Procedure. A performance-based requirement for surface preparation, rather than a prescriptive requirement, is recommended for contract use. That is, it is usually better to describe the characteristics of the cleaned surface (e.g., profile and degree of chalk removal) than to specify the specific materials and procedures to be used. Often the general type of surface preparation (washing, blasting, etc.) is specified, because of job or other constraints, along with requirements for characteristics of the cleaned surface. In this way, the specifier allows the contractor to select the specific equipment, materials and procedures to get the job done and avoids putting contradictory requirements into the job specification.

 

2.1.3 Section Organization. This section is organized into: discussions of repair procedures usually done in conjunction with a painting contract and prior to painting; specific recommendations for surface preparation procedures and standards for specific substrates; recommendations for coating removal; and general background information on surface preparation methods.

 

2.2 Repair of Surfaces. All surfaces should be in good condition before recoating. If repairs are not made prior to painting, premature failure of the new paint is likely. Rotten wood, broken siding, and other deteriorated substrates must be replaced or repaired prior to maintenance painting. Water-associated problems, such as deteriorated roofs and nonfunctioning drainage systems, must be repaired prior to coating. Interior moist spaces, such as bathrooms and showers must be properly vented. Cracks, holes, and other defects should also be repaired.  Areas in need of repair can sometimes be identified by their association with localized paint failures. For example, localized peeling paint confined to a wall external to a bathroom may be due to inadequate venting of the bathroom.

 

2.2.1 Joints, Cracks, Holes, or Other Surface Defects.  Caulks and sealants are used to fill joints and cracks in wood, metal and, in some cases, in concrete and masonry. Putty is used to fill holes in wood. Glazing is used to cushion glass in window sashes. Specially formulated Portland cement materials are available for use in cracks and over spalled areas in concrete. Some of these contain organic polymers to improve adhesion and flexibility. Other materials are available to repair large areas of interior plaster (patching plaster), to repair cracks and small holes in wallboard (spackle), to fill joints between wallboards (joint cement), and to repair mortar.  Before application of these repair materials, surfaces should be clean, dry, free of loose material, and primed according to the written instructions of the material manufacturer.

 

Caulking and sealant compounds are resin based viscous materials. These compounds tend to dry on the surface but stay soft and tacky underneath. Sealants have application properties similar to caulking materials but tend to be more flexible and have greater extendibility than caulks. Sealants are often considered to be more durable than caulks and may also be more expensive. Commonly available generic types of caulks and sealants include oil-based, butyl rubber, acrylic latex, silicone, polysulfide, and polyurethane. The oil-based and butyl-rubber types are continually oxidized by exposure to sunlight and become brittle on aging. Thus, their service life is limited. Acrylic-latex and silicone caulks tend to be more stable and have longer service lives. Applications are usually made with a caulking gun. However, some of these materials may also be available as putties or in preformed extruded beads that can be pressed in place.  Putty and glazing compounds are supplied in bulk and applied with a putty knife. Putties are not flexible and thus should not be used for joints and crevices.  Glazing compounds set firmly, but not hard, and thus retain some flexibility. Rigid paints, such as oil/alkyds, will crack when used over flexible caulking, sealing, and glazing compounds and should not be used.  Acrylic-latex paints, such as TT-P-19, Paint, Latex (Acrylic Emulsion, Exterior Wood and Masonry) are a better choice.

 

2.2.2 Cementitious Surfaces. Epoxy resin systems for concrete repair are described in MIL-E-29245, Epoxy Resin Systems for Concrete Repair. This document describes epoxy repair materials for two types of application. They are: bonding hardened concrete to hardened concrete, and using as a binder in mortars and concrete. These types are further divided into classes based on working temperature. Thus, an appropriate material can be specified.

 

2.3 Recommendations by Substrate. Each different type of construction material may have a preferred surface preparation method. For substrates, grease and oil are usually removed by solvent or steam cleaning and mildew is killed and removed with a hypochlorite (bleach) solution.

 

2.3.1 Wood. Bare wood should not be exposed to direct sunlight for more than 2 weeks before priming. Sunlight causes photo-degradation of surface wood-cell walls. This results in a cohesively weak layer on the wood surface which, when painted, may fail. If exposed, this layer should be removed prior to painting by sanding. Failure of paint caused by a degraded-wood surface is suspected when wood fibers are detected on the backside of peeling paint chips.  When the existing paint is intact, the surface should be cleaned with water, detergent, and bleach as needed to remove surface contaminants, such as soil, chalk, and mildew. When the existing paint is peeling and when leaded paint is not present, loose paint can be removed by hand scraping. Paint edges should be feathered by sanding. Power sanding may damage the wood if improperly done. Water and abrasive blasting are not recommended for wood, because these techniques can damage the wood. When leaded paint is present, special precautions, such as wet scraping, should be taken.

 

 

Table 2 Commonly Used Methods of Surface Preparation for Coatings (IMPORTANT NOTE: Methods may require modification or special control when leaded paint is present.)
Cleaning Method	Equipment	Comments
Organic solvent	Solvent such as mineral spirits, sprayers, rags, etc.	Removes oil and grease not readily removed by other methods; precautions must be taken to avoid fires and environmental contamination; local VOC regulations may restrict use.
Detergent/power washing	Pumps, chemicals, sprayers, brushes	At pressures not exceeding 2000 psi, removes soil, chalk, mildew, grease, and oil, depending upon composition; good for smoke, stain, chalk and dirt removal.
Acid	Chemicals, sprayers, and brushes	Removes residual efflorescence and laitance from concrete after dry brushing. Thoroughly rinse afterwards.
Chemical paint strippers	Chemicals, sprayers, scrapers, washing equipment	Removes coatings from most substrates, but slow, messy, and expensive; may degrade surface of wood substrates.
Steam	Heating system pump, lines, and nozzles	Removes heavy oil, grease, and chalk; usually used prior to other methods.
Water blasting	High pressure water pumps, lines, and nozzles	At pressures of 2000 psi and above, removes loose paint from steel, concrete and wood; can damage wood or masonry unless care is taken; inhibitor generally added to water to prevent flash rusting of steel.
Hand tool	Wire brushes, chipping hammers, and scrapers	Removes only loosely adhering contaminants; used mostly for spot repair; slow and not thorough.
Power tool	Wire brushes, grinders, sanders, needle guns, rotary peeners, etc.	Faster and more thorough than hand tools because tightly adhering contaminants can be removed; some tools give a near-white condition on steel but not an angular profile; slower than abrasive blasting; some tools are fitted with vacuum collection devices.
Heat	Electric heat guns	Can be used to soften coatings on wood, masonry, or steel; softened coatings are scraped away, torches SHOULD NOT be used.
Abrasive blasting	Sand, metal shot, and metal or synthetic grit propelled onto metal by pressurized air, with or without water, or centrifugal force.	Typically used on metal and, with care on masonry; can use recyclable abrasives; special precautions are needed when removing lead containing paint. Water may be added to control dust and its addition may require use of inhibitors. Vacuum blasting reduces dust but is slower than open. Centrifugal blasting is a closed cycle system in which abrasive is thrown by a spinning vaned wheel.

 

 

Paint should be removed from wood when failure is by cross-grain cracking (that is, cracking perpendicular to the wood grain). This failure occurs when the total paint thickness is too thick and/or the paint is too inflexible. Painting over this condition almost always results in early failure of the maintenance paint layer. Paint removal from wood is difficult and may not always be feasible. Chemical strippers can be used, but the alkaline types may damage (chemically degrade) the surface of the wood and cause a future peeling-paint failure. Failure caused by a stripper-degraded wood surface is more likely for exterior exposures than for interior exposures. This is because the greater expansion and contraction of wood in exterior exposures requires that the surface wood have a greater mechanical strength.

 

2.3.2 Concrete/Masonry. Bare concrete and masonry surfaces, as well as painted surfaces, are usually best cleaned with water and detergent. Use low-pressure washing (less than 2000 psi) or steam cleaning (ASTM D 4258) to remove loose surface contaminants from surfaces. Use high-pressure water blasting (greater than 2000 psi and usually about 5000 psi) (ASTM D 4259, Abrading Concrete) to remove loose old coatings or other more tightly held contaminates or chalk. If existing paints are leaded, special worker safety and environmental controls will be needed.  Abrasive blasting (ASTM D 4259 and D 4261, Surface Cleaning Concrete Unit Masonry for Coating) or acid etching of bare surfaces (ASTM D 4260, Acid Etching Concrete) may also be used to obtain a surface profile as well as clean surfaces for coating. Care must be taken to avoid damaging surfaces with high-pressure water or abrasives. Grease and oil must be removed with detergents or steam before abrasive blasting. Any efflorescence present should first be removed by dry wire brushing or acid washing. Special worker safety and environmental controls may be needed.  Concrete surfaces must be completely dry prior to paint application for all types of paints except waterborne. The plastic sheet method (ASTM D 4263, Indicating Moisture in Concrete by the Plastic Sheet Method) can be used to detect the presence of water (i.e., tape a piece of plastic sheet to the surface, wait 24 hours and look for condensed moisture under the sheet - the inside of the sheet should be dry).

 

2.3.3 Steel. The first step in preparing steel for coating is solvent cleaning as described in SSPC SP 1. Cleaning methods described in SSPC SP 1 include organic solvents, vapor

degreasing, immersion in appropriate solvent, use of emulsion or alkaline cleaners, and steam cleaning with or without detergents.  SSPC SP 1 is specifically included as the first step in the SSPC surface preparation procedures.  For large areas of uncoated steel and coated steel with badly deteriorated coatings, the preferred method of removing mill scale, rust and coatings is abrasive blasting (SSPC SP 7, SSPC SP 6, SSPC SP 10, SSPC SP 5). These methods can both clean the surface and produce a surface profile. The specific abrasive method selected depends upon the conditions of the steel, the desired coating life, the environment and the coating to be applied. If leaded paint is present, special precautions must be taken to protect workers and the environment.  High-pressure water blasting, with or without injected abrasives, should be considered if dry abrasive blasting cannot be done because of environmental or worker safety restrictions.  For small localized areas, other cleaning methods such as hand tool cleaning (SSPC SP 2) or power tool cleaning (SSPC

SP 3 or SSPC SP 11) may be more practical.

 

2.3.3.1 Specific Surface Preparation Requirements for Coatings for Steel. Different types of coatings may require different levels of cleaning. Commonly agreed upon minimum requirements are listed below. However, manufacturers of some specific coatings may require or recommend a cleaner surface. Conflicts between manufacturer's written instructions (tech data sheets) and contract specifications should be avoided.

 

Coating                                  Minimum Surface Preparation

Drying Oil                              SSPC SP 2 or SSPC SP 3

Alkyd                                      SSPC SP 6 or SSPC-SP 11

                                    SSPC SP 3 for limited localized areas

Asphaltic                                SSPC SP 6 or SSPC SP 11

Latex                                       SSPC SP 6 or SSPC SP 11

Vinyl Lacquer                       SSPC SP 10

Chlorinated Rubber             SSPC SP 10

Epoxy                                     SSPC SP 6 or SSPC SP 10

Polyurethane                        SSPC SP 10

Organic Zinc                         SSPC SP 6 or SSPC SP 10

Inorganic Zinc                      SSPC SP 10 or SSPC SP 5

 

For immersion or other severe environments, the higher level of the two options should be used. Higher levels may also be used to ensure the maximum lives from coating systems.

 

2.3.4 Galvanized and Inorganic-Zinc Primed Steel. The recommended method of cleaning uncoated galvanized steel varies with the condition of its surface. Simple solvent (organic or

detergent-based) cleaning (SSPC SP 1) is usually adequate for new galvanizing. This will remove oil applied to the galvanizing to protect it during exterior storage. If loose zinc corrosion products or coating are present on either galvanized or inorganic-zinc primed steel, they should be removed by bristle or wire brushing (SSPC SP 2 or SSPC SP 3) or water blasting. The method chosen must successfully remove the contaminants. Uniform corrosion of unpainted galvanizing may expose the brownish iron-zinc alloy. If this occurs, the surface should be painted as soon as possible. If rusting is present on older galvanized or on inorganic-zinc primed steel, remove the rust by sweep abrasive blasting (SSPC SP 7) or using power tools, such as wire brushing (SSPC SP 2, SSPC SP 3). Abrasive blasting is usually more appropriate when large areas are corroded, while the use of hand or power tools may be more appropriate when rusting is localized.  For either method, the procedure should be done to minimize removal of intact galvanizing or of the inorganic zinc primer.  Deteriorated coatings should also be removed using abrasive blasting or hand or power tools. When leaded-coatings are present, special worker safety and environmental precautions must be taken.

 

2.3.5 Aluminum and Other Soft Metals. New, clean aluminum and other soft metals may be adequately cleaned for coating by solvent cleaning (SSPC SP 1). The use of detergents may be required for removal of dirt or loose corrosion products.  Abrasive blasting with plastic beads or other soft abrasives may be necessary to remove old coatings. Leaded coatings will

require special worker safety and environmental precautions.

 

2.4 Standards for Condition of Substrates

 

2.4.1 Unpainted Steel. Verbal descriptions and photographic standards have been developed for stating the condition of existing steel substrates. SSPC VIS 1, Abrasive Blast Cleaned Steel (Standard Reference Photographs) illustrates and describes four conditions of uncoated structural steel. They are:

 

Title                                         Grade

Adherent mill scale              A

Rusting mill scale                B

Rusted                                   C

Pitted and rusted                  D

 

Since the condition of the surface to be cleaned affects the appearance of steel after cleaning, these conditions are used in the SSPC VIS 1 cleanliness standards described below.

 

2.4.2 Nonferrous Unpainted Substrates. There are no standards describing the condition of other building material substrates.

 

2.5 Standards for Cleanliness of Substrates

 

2.5.1 Standards for Cleaned Steel Surfaces

2.5.1.1 SSPC and NACE Definitions and Standards. The SSPC and the NACE Standards are used most frequently for specifying degree of cleanliness of steel surfaces. SSPC has standard definitions and photographs for common methods of cleaning (SSPC VIS 1 and

SSPC VIS 3, Power- and Hand-Tool Cleaned Steel). NACE TM0170, Surfaces of New Steel Air Blast Cleaned With Sand Abrasive; definitions and metal coupons) covers only abrasive blasting.  Volume 2 of SSPC Steel Structures Painting Manual contains all the SSPC standards, as well as other useful information. For both types of standards, the definition, rather than the photograph or coupon, is legally binding.  To use the SSPC or NACE standards, first determine the condition of steel that is to be blasted (e.g., Grade A, B, C, or

D), since different grades of steel blasted to the same level do not look the same. After determining the condition of steel, compare the cleaned steel with the pictorial standards for that condition. The appearance of blasted steel may also depend upon the type of abrasive that is used. NACE metal coupons represent four degrees of cleanliness obtained using one of three types of abrasives - grit, sand, or shot.

2.5.1.2 Job-Prepared Standard. A job-specific standard can be prepared by blasting or otherwise cleaning a portion of the structure to a level acceptable to both contractor and

contracting officer, and covering it with a clear lacquer material to protect it for the duration of the blasting. A 12-inch steel test plate can also be cleaned to an acceptable level and sealed in a water- and grease-proof bag or wrapper conforming to MIL-B-131, Barrier Materials, Water Vaporproof, Greaseproof, Flexible, Heat-Sealable.

 

2.5.1.3 Pictorial Standards for Previously Painted Steel.  Photographic standards for painted steel are available in the Society for Naval Architects and Engineers Abrasive Blasting

Guide for Aged or Coated Steel Surfaces. Pictures representing paint in an original condition and after each degree of blasting are included.

 

 

 

Table 3 SSPC and NACE Standards for Cleaned Steel Surfaces
Method	SSPC No.	NACE No.	Intended Use
Solvent Cleaning	SP 1		Removal of oil and grease prior to further cleaning by another method
Hand Tool	SP 2		Removal of loose mill scale, rust, and paint
Power Tool	SP 3		Faster removal of loose mill scale, rust, and coatings than hand tool cleaning
White Metal Blast	SP 5	1	Removal of visible contaminants on steel surfaces; highest level of cleaning for steel
Commercial Blast	SP 6	3	Removal of all visible contaminants except that one third of a steel surface may have shadows, streaks, or stains
Brush-off Blast	SP 7	4	Removal of loose mill scale, rust, and paint (loose paint can be removed with dull putty knife)
Pickling	SP 8		Removal of mill scale and rust from steel
Near-white Blast	SP 10	2	Removal of visible contaminants except that 5 percent of steel surfaces may have shadows, streaks, or stains
Power Tool Cleaning	SP 11		Removal of visible contaminants (surface is comparable to SSPC SP 6, also provides profile)

 

2.6 Recommendations for Paint Removal. It is often necessary to remove old coatings that are peeling, checking, cracking, or the like. General recommendations for removal of

paint from a variety of substrates are made in Table 4.

 

 

Table 4 Procedures for Coating Removal (IMPORTANT NOTE - Presence of Leaded Paint Will Require Environmental and Worker Safety Controls)
Substrate	Methods
Wood	Chemical removers; heat guns or hot plates along with scraping; power sanding (must be done with caution to avoid damaging wood).
Masonry	Careful water blasting to avoid substrate damage; brush-off blasting and power tools, used with caution.
Steel	Abrasive blasting; water blasting.
Miscellaneous metals	Chemicals; brush-off blast; water blast

 

2.7 Methods of Surface Preparation. Information on surface preparation methods and procedures are presented to help select appropriate general procedures and to inspect surface preparation jobs. It is not intended to be a complete source of information

for those doing the work.

 

2.7.1 Abrasive Blasting. Abrasive blast cleaning is most often associated with cleaning painted and unpainted steel. It may also be used with care to prepare concrete and masonry

surfaces and to clean and roughen existing coatings for painting.  Abrasive blasting is an impact cleaning method. High-velocity abrasive particles driven by air, water, or centrifugal force impact the surface to remove rust, mill scale, and old paint from the surfaces. Abrasive cleaning does not remove oil or grease.  If the surface to be abrasive blasted is painted with leaded paint, additional controls must be employed to minimize hazards to workers and the surrounding environment.  There are four degrees of cleanliness of blast cleaning designated by the SSPC and the NACE for steel substrates. These designations are white metal, near-white metal, commercial, and brush-off.  The degree of cleanliness obtained in abrasive blasting depends on the type of abrasive, the force with which the abrasive particles

hits the surface, and the dwell time.

 

2.7.1.1 Types of Abrasive Blasting

a) Air (Conventional). In conventional abrasive blasting, dry abrasive is propelled against the surface to be cleaned so that rust, contaminates, and old paint are removed by the impact of the abrasive particles. The surface must be cleaned of blasting residue before painting. This is usually done by blowing clean air across the surfaces. Special care must be taken to ensure that horizontal or other obstructed areas are thoroughly cleaned. Uncontrolled abrasive blasting is restricted in most locations because of environmental regulations. Consult the local industrial hygiene or environmental office for regulations governing local actions.  Procedures for containment of blasting debris are being used for paint removal from industrial and other structures. The SSPC has developed a guide (SSPC Guide 6I) for selecting containment procedures depending upon the degree of containment desired. The amount of debris generated can be reduced by recycling the abrasive. Recycling systems separate the paint waste from the abrasive.

 

b) Wet. Wet-abrasive blasting is used to control the amount of airborne dust. There are two general types of wet abrasive blasting. In one, water is injected near the nozzle exit into the stream of abrasive. In the other, water is added to the abrasive at the control unit upstream of the nozzle and the mixture of air, water, and sand is propelled through the hose to the nozzle. For both types of wet-blasting, the water may contain a corrosion inhibitor. Inhibitors are generally sodium, potassium, or ammonium nitrites, phosphates or dichromates. Inhibitors must be chosen to be compatible with the primer that will be used. After wet blasting, the surface must be rinsed free of spent abrasive. (The rinse water should also contain a rust inhibitor when the blasting water does.) Rinsing can be a problem if the structure contains a large number of ledges formed by upturned angles or horizontal girders since water, abrasives, and debris tend to collect in these areas. The surface must be completely dry before coating. When leaded paint is present, the water and other debris must be contained and disposed of properly. This waste may be classified as a hazardous waste under Federal and local regulations, and must be handled properly.

 

c) Vacuum. Vacuum blasting systems collect the spent abrasives and removed material, immediately adjacent to the point of impact by means of a vacuum line and shroud surrounding the blasting nozzle. Abrasives are usually recycled. Production is slower than open blasting and may be difficult on irregularly shaped surfaces, although shrouds are available for non-flat surfaces. The amount of debris entering the air and the amount of cleanup is kept to a minimum if the work is done properly (e.g., the shroud is kept against the surface). This procedure is often used in areas where debris from open air blasting or wet blasting cannot be tolerated.

 

Table 5 Procedures for Coating Removal (IMPORTANT NOTE - Presence of Leaded Paint Will Require Environmental and Worker Safety Controls)
Substrate	Methods
Wood	Chemical removers; heat guns or hot plates along with scraping; power sanding (must be done with caution to avoid damaging wood).
Masonry	Careful water blasting to avoid substrate damage; brush-off blasting and power tools, used with caution.
Steel	Abrasive blasting; water blasting.
Miscellaneous metals	Chemicals; brush-off blast; water blast

 

d) Centrifugal. Cleaning by centrifugal blasting is achieved by using machines with motor-driven bladed wheels to hurl abrasives at a high speed against the surface to be cleaned.  Advantages over conventional blasting include savings in time, labor, energy, and abrasive; achieving a cleaner, more uniform surface; and better environmental control. Disadvantages of centrifugal blasting include the difficulty of using it in the field, especially over uneven surfaces, although portable systems have been developed for cleaning structures such as ship hulls and storage tanks. Robots may be used to guide the equipment. In many cases, the abrasive used is reclaimed and used again.

 

2.7.1.2 Conventional Abrasive Blasting Equipment. Components of dry abrasive blasting equipment are air supply, air hose and couplings, abrasive blast machines, abrasive blast hose and couplings, nozzles, operator equipment, and oil and moisture separators. A brief description of each component follows:

 

a) Air Supply. The continuous and constant supply of an airstream of high pressure and volume is one of the most critical parts of efficient blasting operations. Thus, the air supply (compressor) must be of sufficient capacity. Insufficient air supply results in excessive abrasive use and slower cleaning rates. The compressor works by taking in, filtering, and compressing a large volume of air by rotary or piston action and then releasing it via the air hose into the blasting machine.  The capacity of a compressor is expressed in volume of air moved per unit time (e.g., cubic feet per minute (cfm)) and is directly related to its horsepower. The capacity required depends upon the size of the nozzle orifice and the air pressure at the nozzle. For example, a flow of 170 to 250 cfm at a nozzle pressure of 90 to 100 psi is necessary when using a nozzle with a 3/8 to 7/16 inch orifice. This typically can be achieved with a 45 to 60 horsepower engine.

 

b) Air-Supply Hose. The air-supply hose delivers air from the compressor to the blasting machine. Usually the internal diameter should be three to four times the size of the nozzle orifice. The length of the hose should be as short as practical because airflow through a hose creates friction and causes a pressure drop. For this reason, lines over 100 feet long generally have internal diameters four times that of the nozzle orifice.

 

c) Blasting Machine. Blasting machines or "sand pots" are the containers which hold the abrasives. The capacity of blasting machines varies from 50 pounds to several tons of abrasive material. The blasting machine should be sized to maintain an adequate volume of abrasive for the nozzles.

 

d) Abrasive Blasting Hose. The abrasive blasting hose carries the air and abrasive from the pot to the nozzle. It must be sturdy, flexible, and constructed or treated to prevent electrical shock. It should also be three to four times the size of the nozzle orifice, except near the nozzle end where a smaller diameter hose is attached.

 

e) Nozzles. Nozzles are available in a great variety of shapes, sizes, and designs. The choice is made on the basis of the surface to be cleaned and the size of the compressor. The Venturi design (that is, large throat converging to the orifice and then diverging to the outlet, Figure 3) provides increased speed of abrasive particles through the nozzle as compared with a straight bore nozzle. Thus, the rate of cleaning is also increased. Nozzles are available with a variety of lengths, orifice sizes, and lining materials. The life of a nozzle depends on factors such as the lining material and the abrasives and varies from 2 to 1500 hours. Nozzles should be inspected regularly for orifice size and wear. Worn nozzles result in poor cleaning patterns and efficiency.

 

f) Oil/Moisture Separators. Oils used in the compressor could contaminate the air supply to the nozzles. To combat this, oil/moisture separators are installed at the blast machine. The separators require periodic draining and routine replacement of filters. Contamination of the air supply can be detected by a simple blotter test. In this test, a plain, white blotter is held 24 inches in front of the nozzle with only the air flowing (i.e., the abrasive flow is turned off) for 1 to 2 minutes. If stains appear on the blotter, the air supply is contaminated and corrective action is required. ASTM D 4285, Indicating Oil or Water in Compressed Air describes the testing procedure in more detail.

 

g) Operators Equipment. The operator’s equipment includes a protective helmet and suit. The helmet must be air-fed when blasting is done in confined or congested areas. To be effective it must furnish respirable air to the operator at a low noise level, protect the operator from rebounding abrasive particles, provide clear vision to the operator, and be comfortable and not restrictive. Air-fed helmets must have National Institute of Safety and Hygiene (NIOSH) approval.

 

h) Wet Blasting. In addition to equipment needed for dry abrasive blasting, metering, delivery, and monitoring devices for water are needed.

 

i) Vacuum Blasting. Although there are many designs for vacuum blasting equipment, all systems have a head containing a blast nozzle, surrounded by a shroud connected to a vacuum system, and a collection chamber for debris.

 

j) Centrifugal Blasting. In centrifugal blasting, abrasive is hurled by wheels instead of being air-driven. This type of blasting is often used in shop work. Portable devices have been developed for use on flat surfaces. Abrasive is contained and usually recycled.

 

2.7.1.3 Abrasive Properties. The SSPC has a specification for mineral and slag abrasive, SSPC AB 1, Mineral and Slag Abrasives. Abrasives covered by the specification are intended primarily for one-time use without recycling. The specification has requirements for specific gravity, hardness, weight change on ignition, water soluble contaminant, moisture content and oil content.  These and other properties of abrasives are discussed below:

 

a) Size. Abrasive size is a dominant factor in determining the rate of cleaning and the profile obtained. A large abrasive particle will cut deeper than a small one of the same shape and composition, however, a greater cleaning rate is generally achieved with smaller-sized particles. Thus, a mix is generally used.

 

b) Shape. The shape and size of abrasive particles determine the surface profile obtained from blasting.  Round particles, such as shot, produce a shallow, wavy profile.  Grit, which is angular, produces a jagged finish. Usually a jagged finish is preferred for coating adhesion. Round particles are well suited for removal of brittle contaminants like mill scale and are also used when little or no change in surface configuration is permitted. Sand and slag, which are semi-angular, produce a profile that is somewhere between that of shot and grit. Currently, sand is used much less than other abrasives because of health and breakdown factors.

 

c) Hardness. Hard abrasives usually cut deeper and faster than soft abrasives. Hence, hard abrasives are best suited for blast cleaning jobs where the objective is to remove surface coatings. Soft abrasives, such as walnut hulls, can remove light contaminants without disturbing a metal substrate or, in some cases, the existing coating system.

 

d) Specific Gravity. Generally the more dense a particle, the more effective it is as an abrasive. This is because it takes a certain amount of kinetic energy to remove contaminants from the surface and the kinetic energy of an abrasive particle is directly related to its density (specific gravity).

 

e) Breakdown Characteristics. Abrasive particles striking the surface at high speeds are themselves damaged. The way in which they fracture (breakdown) and/or in which they change their shape and size is called their breakdown characteristic. An excessive breakdown rate results in a significant increase in dusting, requires extra surface cleaning for removal of breakdown deposits, and limits the number of times the abrasive can be reused.

 

f) Water-Soluble Contaminants. ASTM D 4940, Conductimetric Analysis of Water Soluble Ionic Contamination of Blasting Abrasives describes a conductivity test for determining the level of contamination of metallic, oxide, slags, and synthetic abrasives by water-soluble salts. SSPC AB 1 requires that the conductivity of the test solution be below 100 microsiemens.

 

2.7.1.4 Abrasive Types. Abrasives fall into seven general categories: metallic, natural oxides, synthetic, slags, cellulose (such as walnut hulls), dry ice pellets (carbon dioxide), sodium bicarbonate, and sponge.

 

a) Metallic. Steel shot and grit are the most commonly used metallic abrasives. Metallic abrasives are used to remove mill scale, rust, and old paint and provide a suitable anchor pattern. The advantages of metallic abrasives include longer useful life (can be recycled many times), greater impact energy for given particle size, reduced dust formation during blasting, and minimal embedment of abrasive particles. The disadvantages include blast cleaning equipment must be capable of recycling, abrasives must be kept dry to prevent corrosion, and the impact of steel shot on metal surfaces may cause formation of hackles on the surface. These hackles are relatively long slivers of metal and must be removed mechanically by sanding or grinding before coating to prevent pinpoint corrosion through the paint film.

 

b) Natural Oxides. Silica is the most widely used natural oxide because it is readily available, low in cost, and effective. Sand particles range from sharply angular to almost spherical, depending on the source. OSHA and EPA regulations have restricted the use of sand in many areas. Non-silica sands (generally termed "heavy mineral" sands) are also being used for blast cleaning. However, they are generally of finer particle size than silica sand and are usually more effectively used for cleaning new steel than for maintenance applications.

 

c) Synthetics. Aluminum oxide and silicon carbide are nonmetallic abrasives with cleaning properties similar to the metallics and without the problem of rusting. They are very hard, fast-cutting and low-dusting, but they are costly and must be recycled for economical use. They are often used to clean hard, high tensile strength metals.

 

d) Slags. The most commonly used slags for abrasives are by-products from metal smelting (metal slags) and electric power generation (boiler slags). Slags are generally hard, glassy, homogeneous mixtures of various oxides. They usually have an angular shape, a high breakdown rate, and are not suitable for recycling.

 

e) Cellulose Type. Cellulose type abrasives, such as walnut shells and corncobs, are soft, low density materials used for cleaning of complex shaped parts and removing dirt, loose paint, or other deposits on paint films. Cellulose type abrasives will not produce a profile on a metal surface.

 

f) Dry Ice. Special equipment is used to convert liquid carbon dioxide into small pellets which are propelled against the surface. Since the dry ice sublimes, the abrasive leaves no residue. The method can be used to remove paint from some substrates, but not mill scale and will not produce a profile. Paint removal is slow (and very difficult from wood) and the equipment needed to carry out the blasting is expensive.

 

g) Sponge. Specially manufactured sponge particles, with or without impregnated hard abrasive, are propelled against the surface. Less dust is created when sponge abrasive is used as compared to expendable or recyclable abrasives. The sponge is typically recycled several times. If sponge particles with impregnated hard abrasive are used, a profile on a metal can be produced. Sponge blasting is typically slower than with conventional mineral or steel abrasives.

 

h) Sodium Bicarbonate. Sodium bicarbonate particles are propelled against the surface, often in conjunction with high-pressure water. This method provides a way to reduce waste if the paint chips can be separated from the water after cleaning since sodium bicarbonate is soluble in water. These particles can be used to remove paint, but not mill scale or heavy corrosion.

 

2.7.1.5 Selection. Selection of the proper abrasive is a critical part of achieving the desired surface preparation.  Factors that influence the selection include: desired degree of cleanliness; desired profile; degree of rusting; deep pits; and kind and amount of coating present. Since obtaining the desired degree of cleanliness and profile are the main reasons for impact cleaning, they must be given priority over all other factors except environmental ones in abrasive selection.

2.7.1.6 Inspection. Abrasives must be dry and clean. It is most important that they are free of inorganic salts, oils, and other contaminants. There are only limited standard procedures for inspecting abrasives. The following general procedure is suggested:

 

a) Visually inspect the abrasive to ensure that it is dry,

 

b) Test for presence of water soluble salts by following ASTM D 4940 in which equal volumes of water and abrasive are mixed and allowed to stand for several minutes and the conductivity of the supernatant is measured using a conductivity cell and bridge,

 

c) Examine the supernatant of the ASTM D 4940 test for presence of an oil film.

 

2.7.1.7 Procedures/General Information. Good blasting procedures result in efficient and proper surface preparation.  Adequate pressure at the nozzle is required for effective blasting. Other factors, such as flow of abrasive, nozzle wear, position of the nozzle with respect to the surface, and comfort of operator are also important. A well trained operator is essential to obtaining an acceptable job.

 

a) Handling the Nozzle. The angle between the nozzle and the surface and the distance between the nozzle and surface are important factors in determining the degree and rate of cleaning. The working angle will vary from 45 to 90 degrees depending upon the job. To remove rust and mill scale, the nozzle is usually held at an angle of between 80 and 90 degrees to the surface. This is also the preferred configuration for cleaning pitted surfaces. A slight downward angle will direct the dust away from the operator and ensure better visibility. A larger angle between nozzle and surface allows the operator to peel away heavy coats of old paint and layers of rust by forcing the blast under them. Other surface contaminants may be better removed with a cleaning angle of from 60 to 70 degrees.  By varying the distance between the nozzle and the surface, the type and rate of cleaning can also be varied. The closer the nozzle is to the surface, the smaller the blast pattern and the more abrasive strikes it. Thus, a greater amount of energy impacts the surface per unit area than if the nozzle were held further away. A close distance may be required when removing tight scale, for example. However, a greater distance may more effectively remove old paint. Once an effective angle and distance have been determined, each pass of the nozzle should occur in a straight line to keep the angle and distance between the nozzle and the surface the same. Arcing or varying the distance from the surface will result in a nonuniform surface.

 

b) Rates. The rate of cleaning depends on all of the factors discussed above. Abrasive blasting of steel to a commercial degree of cleanliness (SSPC SP 6 or better) is much

slower than painting. No more steel surface area should be blast cleaned at one time than can be primed the same day, since significant rusting can occur overnight. If rusting does occur, the surface must be reblasted before painting.

 

2.7.2 Acid Cleaning. Acid cleaning is used for cleaning efflorescence and laitance from concrete.

 

2.7.2.1 Concrete. Heavy efflorescence and laitance should be removed from concrete surfaces by dry brushing or cleaning prior to acid cleaning. This is to prevent dissolution of the

efflorescence and subsequent movement of the salts into the concrete. Prior to application of an acid solution, heavy oil, grease, and soil deposits must also be removed. Oily dirty deposits can be removed by solvent or detergent washing. The commonly used procedure to acid clean these surfaces is to thoroughly wet the surface with clean water; uniformly apply acid solution (often a 5 to 10 percent solution of hydrochloric (muriatic) acid solution or a solution of phosphoric acid); scrub the surface with a stiff bristle brush; and immediately rinse the surface thoroughly with clean water. Measure the pH of the surface and rinse water using pH paper (ASTM D 4262, pH of Chemically Cleaned or Etched Concrete Surfaces). In general, the pH should be within one pH unit of fresh rinse water. It is essential for good paint performance that the acid be neutralized before painting. Work should be done on small areas, not greater than 4 square feet in size. This procedure or light abrasive blasting can also be used to etch the surface of very smooth concrete prior to coating. Coating adhesion on slightly rough concrete surfaces is usually much better than on smooth and (e.g., troweled) surfaces. An acid etched surface is usually roughened to a degree similar in appearance to a medium grade sandpaper. This cleaning method is described in detail in ASTM D 4260.

 

2.7.3 Chemical Removal of Paint. Paint strippers can be used when complete paint removal is necessary and other methods, such as abrasive blasting, cannot be used due to environmental restraints or potential damage to the substrate. Removers are selected according to the type and condition of the old coating as well as the nature of the substrate. They are available as flammable or nonflammable types and in liquid or semi-paste types. While most paint removers require scraping or other mechanical means to physically remove the softened paint, types are available that allow the loosened coating to be flushed away with steam or hot water. If paint being removed contains lead, additional environmental and worker safety precautions will be needed. Many removers contain paraffin wax to retard evaporation and this residue must be removed prior to recoating. Always follow manufacturer's recommendations. In addition, surrounding areas (including shrubs, grass, etc.) should be protected from exposure to the remover, collection of the residue will probably be required by environmental regulations. Removers are usually toxic and may cause fire hazards. Management of the waste associated with the procedure will also be necessary. Consult the local environmental and safety offices for further information.

 

2.7.4 Detergent Washing. Detergent washing or scrubbing is an effective way to remove soil, chalk and mildew. Detergent cleaning solutions may be applied by brush, rags, or spray. An

effective solution for removal of soil and chalk is 4 ounces of trisodium phosphate, 1 ounce household detergent, and 4 quarts of water. For mildew removal, 1 part of 5 percent sodium hypochlorite solution (household bleach) is added to 3 parts of the cleaning solution used for chalk and soil removal. Of course, if there is little or no existing chalk on the surface, the cleaning solution should not contain the trisodium phosphate. Note, that sodium hypochlorite solution (household bleach) must not be added to cleaning solutions containing ammonia or other similar chemicals. Toxic fumes will be produced. Thorough rinsing with water is absolutely necessary to remove the soapy alkaline residues before recoating. To test the effectiveness of the rinse, place pH paper against the wet substrate and in the rinse water and compare the pH of the two. (Refer to ASTM D 4262 for complete description of the procedure.) The pH of the substrate should be no more than one pH unit greater than that of

the rinse water.

 

2.7.5 Hand Tool Cleaning. Hand cleaning is usually used only for removing loosely adhering paint or rust. Any grease or oil must be removed prior to hand cleaning by solvent washing. Hand cleaning is not considered an appropriate procedure for removing tight mill scale or all traces of rust and paint. It is slow and, as such, is primarily recommended for spot cleaning in areas where deterioration is not a serious factor or in areas inaccessible to power tools. Hand tools include wire brushes, scrapers, abrasive pads, chisels, knives, and chipping hammers. SSPC SP 2 describes standard industrial hand-tool cleaning practices for steel. Since hand cleaning removes only the loosest contaminants, primers applied over hand-tool cleaned surfaces must be chosen that are capable of thoroughly wetting the surface. Paint performance applied to hand-cleaned steel surfaces is not as good as that applied over blast cleaned surfaces.

 

2.7.6 Heat. Electric heat guns and heat plates are used to remove heavy deposits of coatings on wood and other substrates.  The gun or plate is positioned so that the coating is softened

and can be removed by scraping. Production rates depend upon the thickness of the old coating and the smoothness of the substrate.  There is a possibility of creating toxic fumes, or conditions in which burns are possible. The use of torches is not recommended, although they have been used to remove greasy contaminates and paints from surfaces prior to painting. This is an extremely dangerous procedure. The SSPC no longer has a surface

preparation standard for flame cleaning because of the danger involved.

 

2.7.7 Organic Solvent Washing. Solvent cleaning is used for removing oil, grease, waxes, and other solvent-soluble matter from surfaces. VOC rules may prohibit or limit the use of

solvent cleaning. The local environmental and safety office should be consulted before using or specifying solvent cleaning.  Inorganic compounds, such as chlorides, sulfates, rust, and mill scale are not removed by solvent cleaning. Solvent cleaning or detergent or steam washing must precede mechanical cleaning when oil and grease are present on the surface because mechanical and blast cleaning methods do not adequately remove organic contaminants and may spread them over the surface. Before solvent washing, any soil, cement splatter, or other dry contaminants must first be removed. The procedure for solvent

washing is to: wet the surface with solvent by spraying or wiping with rags wet with solvent; wipe the surface with rags; and make a final rinse with fresh solvent. Fresh solvent must be

used continuously and the rags must be turned and replaced continuously. Solvents rapidly become contaminated with oils and grease since they clean by dissolving and diluting contaminants.  Mineral spirits is effective in most solvent cleaning operations. SSPC SP 1 describes recommended industry practices for cleaning steel using solvents.  Organic solvents pose health and safety threats and should not come into contact with the eyes or skin or be used near sparks or open flames.  Disposal of solvent must be done in accordance with governing regulations. Rags must be placed in fireproof containers after use.

 

2.7.8 Power Tool Cleaning. Power tool cleaning can be used to remove more tightly adhering contaminants and existing paint than hand tool cleaning. Either electrical or pneumatic power is used as the energy source. Power tool cleaning is recommended when deterioration is localized, deterioration is not a serious problem, or when abrasive blasting is not possible. SSPC SP 3 and SSPC SP 11 describe the use of some of these tools for steel.

In general, power tool cleaning is less economical and more time consuming than blasting for cleaning large areas. However, power tools do not leave as much residue or produce as much dust as abrasive blasting. Also, some power tools are equipped with vacuum collection devices. Power tools include sanders, grinders, wire brushes, chipping hammers, scalers, needle guns, and rotary peeners. Power tools clean by impact or abrasion or both. Near-white (i.e., rust and paint removed) steel surfaces with anchor patterns (although different than those achieved in blast cleaning) can be obtained with some power tools, as described in SSPC SP 11. Care must be taken when using wire brushes to avoid burnishing the surface and thus causing a reduced adhesion level of the primer coating. Grease and oil must be removed prior to power tool cleaning. Danger from sparks and flying particles must always be anticipated. The operator and adjacent workers must wear goggles or helmets and wear protective clothing. No flammable solvents should be used or stored in the area.

 

2.7.9 Steam Cleaning. A high-pressure jet of steam (about 300 degrees F, 150 psi), usually with an added alkaline cleaning compound, will remove grease, oil, and heavy dirt from surfaces by a combination of detergent action, water, heat and impact (refer to SSPC SP 1). The steam is directed through a cleaning gun against the surface to be cleaned. The pressure is adjusted to minimize spraying time. Any alkaline residue remaining on the surface after the cleaning operation must be removed by thorough rinsing with fresh water. Alkali cleaners used in steam cleaning may attack aluminum and zinc alloys and should not be used on

these substrates. Steam cleaning may cause old paints to swell and blister. Thus, when steam cleaning previously painted surfaces, the cleaning procedure should first be tested in a

small area to assess the effect on the old paint.  Steam cleaning equipment is usually portable and is one of two designs. With one type of equipment, concentrated cleaning solution is mixed with water, fed through a heating unit so that it is partially vaporized, pressurized, and forced through a nozzle. With another type of equipment, sometimes called a hydro-steam unit, steam from an external source is mixed with the cleaning solution in the equipment or in the nozzle of the cleaning gun. The shape of the nozzle is chosen according to the contour of the surface being cleaned. Steam cleaning is dangerous and extreme caution should be exercised with the equipment. A dead man valve must be included in the equipment and the operator must have sound, safe footing. Workers engaged in steam cleaning operations must be protected from possible burns and chemical injury to the eyes and skin by protective clothing, face shields, and the like.

 

2.7.10 Water Blast Cleaning. Water blast cleaning uses a high-pressure water stream to remove lightly adhering surface contaminants. Selection of water pressure and temperature and addition of a detergent depend on the type of cleaning desired.  Low pressure - up to 2000 psi - (sometimes called "power washing") is effective in removing dirt, mildew, loose paint, and chalk from surfaces. It is commonly used on metal substrates and generally does little or no damage to wood, masonry, or concrete substrates. For removing loose flaky rust and mill scale from steel, water pressures as high as 10,000 psi or more and volumes of water to 10 gallons per minute are used. However, water blasting without an added abrasive does not provide a profile.  By introducing abrasives into the water stream, the cleaning process becomes faster and an anchor pattern is produced.  Hydroblasting at high pressures can be dangerous and extreme caution should be exercised with the equipment. A dead man valve must be included in the equipment and the operator must have sound, safe footing. He should wear a rain suit, face shield, hearing protection, and gloves. Additional safety equipment may be needed.

 

2.7.10.1 Equipment. The basic water blasting unit (without injection of an abrasive) consists of an engine-driven pump, inlet water filter, pressure gauge, hydraulic hose, gun, and nozzle combination. As with the equipment for abrasive blasting, the gun must be equipped with a "fail-safe" valve so that the pressure is relieved when the operator releases the trigger.  Nozzle orifices are either round or flat. The selection depends on the shape of the surface to be cleaned. Flat orifices are usually used on large flat surfaces. Nozzles should be held about 3 inches from the surface for most effective cleaning.

 

CHAPTER 3

ANALYSIS OF PAINT FAILURES

 

1. DEFINITION. Organic coatings deteriorate and fail with time. Failure analysis does not concern itself with this type of deterioration. It is defined as an investigation to determine the cause or causes of premature deterioration of coatings or coating systems. It is obvious, however, that failure analyses are often also directed at obtaining additional information than that stated in the above definition. Thus, the failure analyst may also wish to determine the extent of the damage, whether all requirements of a specification of a contract or work order had been met, who might be responsible for the failure and thus be liable for repairs, or what is the best remedial action to correct the existing condition.

 

2. DOCUMENTATION OF FINDINGS. Measurements, photographs, specimens, and other observations made at the job-site or later in the laboratory should be firmly documented with dates, locations, etc., because they may at a later time become legal evidence. Personnel conducting failure analyses should routinely follow the procedures necessary for such documentation to prepare for any eventuality.

 

3. SCOPE OF FAILURE ANALYSIS. Paint failure analysis can be conducted by anyone with a basic understanding of coatings. However, they are best conducted by someone specially trained for the work. This is particularly true if the investigation becomes part of a dispute, since credibility of the analyst may be a determining factor in a dispute. In some instances, an analysis need not be extensive, but care must be taken not to make important conclusions based on superficial observations. A complete paint failure analysis includes most or all of the following actions:

 

a) Review of specification including modifications

b) Review of supplier’s data

c) Review of inspector’s daily reports

d) Thoroughly documented on-site inspection

e) Laboratory analysis of retained and/or field samples

f) Analysis of data

g) Preparation of a report containing findings and conclusions

 

3.1 REVIEW OF SPECIFICATION FOR COATING WORK. The specification and the submittals required in the specification for the coating work should be thoroughly reviewed and understood. The specification states precisely the work that was to have been done and the methods and materials that were to be used, so that any deviations from them should become apparent. The review may also point out discrepancies or lack of clarity in the document that may have contributed to the failure.

 

3.2 REVIEW OF SUPPLIER’S DATA. Supplier data sheets should be reviewed, because they describe the intended purpose of the coatings used, along with recommended surface preparation and application practices. They may also include compositional information that can be checked later by laboratory analysis to determine if the batch actually used was properly prepared.

 

3.3 REVIEW OF INSPECTOR’S DAILY REPORTS. The inspector’s daily reports should be reviewed, because they provide information about the conditions under which the work was accomplished and the quality of the surface preparation and coating application. Any compromises in the conditions required by the specification or recommended by the supplier may lead to early failure. These reports may also reveal field changes that were made to the original specification.

 

3.4 ON-SITE INSPECTION. Just as the inspector on the job, the person analyzing paint failures must have access to areas where failures have occurred. This may require ladders or lift equipment, lighting, or mirrors. The analyst should also have photographic equipment to document conditions and be skilled in its use. Scales should be used to show relative size, and permanent markings should be made on each photographic exposure for positive identification. Dates should also be placed on the photographs. The analyst should have a standard kit of field test equipment including one or more thickness gages and calibration standards, a knife, a hand lens, and containers for samples. Obviously, he should be well trained in their use and use them systematically, as described elsewhere in this text. A container of methyl ethyl ketone (MEK) or other strong solvent may be useful in either determining paint solubility (e.g., verifying the general paint type or its complete cure) or to strip off a coating to examine the condition of the underlying surface or the thickness of the underlying galvanizing or other insoluble coating. Standard forms for manually recording data or equipment for voice recording are also very useful. A failure analysis checklist can ensure that no important item is overlooked. Obviously, all items on the list may not be important at all times, but to inadvertently skip an important one may be a serious oversight.

 

3.5 ON-SITE INSPECTION TECHNIQUES. An overall visual analysis should first be made to determine the areas where the deterioration is most extensive and where any apparent deviation from specification may have occurred. This should then be followed by a closer examination as to the specific types of deterioration that may be present.

 

a) Use of a hand lens may provide information not otherwise visually apparent. All types of failure, including color changes and chalking, should be described fully. For example, does peeling occur between coats or from the substrate? Are blisters broken or filled with water? This detailed information may be necessary for finalizing conclusions as to the type of failure. The terms defined later in this section should be used to describe failures rather than locally used terms that may not be clear to other people. Care must be taken not to come to final conclusions until all the data are analyzed. It is a good practice to state at the inspection site that the final conclusions on causes of failure cannot be made until completion of laboratory testing.

 

b) Dry film thicknesses should be routinely measured and recorded, as any significant deviations from recommended thicknesses can be a factor contributing to coating failure. The procedure for measurement of these thicknesses required in the specification should be followed.

 

c) Other measurements that may be important are coating adhesion and hardness, since they may provide important information on application or curing of the coating. Adhesion can be easily determined with a simple tape test or by using more sophisticated instrumentation.  Hardness can be tested in the field with a knife or special hardness pencils.

 

d) It is generally important to verify the identity of the finish coatings and occasionally the identity of the entire coating system. If wet samples of the paints used have been retained, they can be submitted for laboratory analysis for conformance to specification or manufacturer’s data sheet. If these are not available, a simple solvent rub test may be useful in determining whether the exterior coatings are thermoplastic, thermosetting, or bituminous. A cotton-tipped swab stick is dipped in MEK or acetone and rubbed against the paint surface. A thermosetting coating such as a vinyl which has been deposited on the surface by simple solvent evaporation will redissolve in the solvent and be wiped onto the cotton. A bituminous (coal tar or asphalt) coating will also behave in this manner, but it will impart a characteristic brown stain to the cotton. Properly cured multiple-component thermosetting coatings such as epoxies that cure by chemical reaction will not be affected by the solvent. These solvents can also be used at the job site to remove thermoplastic coatings to examine the condition of the underlying substrate. The presence of mill scale may establish the extent of surface cleaning. If rust is found, care must be taken to determine if it was present before painting or resulted from underfilm corrosion. Samples of the finish coat can also be removed by sanding and taken to the laboratory for identification.

 

e) Once the various types of failure that may be present have been identified, the extent of each type of deterioration should be estimated. Standard block methods that help to quantify the extent of coating deterioration are described in ASTM F 1130, Inspecting the Coating System of a Ship. Two sets of drawings are used to illustrate failures. One set is used to identify the portion of the surface on which the paint is deteriorated. The other set is used to identify the level of deterioration within the deteriorated areas. For example, a fourth of the surface could exhibit blistering and within the areas 10 percent of the surface could be blistered.

 

3.6 LABORATORY TESTING. A more definitive laboratory analysis of deteriorated paint is generally desired and may become critical if the problem goes into litigation. Such analyses require several representative paint samples to be collected at the job site. Peeled and blistered paint is easily sampled, but it may be necessary to obtain samples from sound paint by scraping or sanding. Each sample should be placed in a sealed container and properly identified and dated. Chain of custody procedures (ASTM D 4840, Sampling Chain of Custody Procedures) should be used if litigation is involved. If samples of wet paint used on the job are available, they can be tested by standard laboratory tests for conformance to any SSPC, or specification referenced in the contract specification. If none of these standards was referenced in the specification, the paints can be tested for conformance to manufacturer’s listed composition or properties.

 

3.6.1 MICROSCOPIC EXAMINATION. Samples of paint collected at the job site should be examined under a light microscope. An edge examination may reveal the number of coats and the thickness of each coat. An examination of the surface may reveal fine cracking or other irregularities. Examination under a scanning electron microscope (SEM) can reveal much more detailed information about the paint film. Also, the SEM often has an attachment for energy dispersive x-ray analysis which can identify the metals and other elements in the pigment portion of small areas of the coating.

 

3.6.2 SPOT TESTS. There are several simple laboratory spot tests that can be run on samples of deteriorated paint collected at the job site. They generally provide specific information about the paint binder (ASTM D 5043, Field Identification of Coatings) or pigment. Special chemicals and training are usually required by the analyst.

 

3.6.3 INFRARED SPECTROPHOTOMETRIC ANALYSIS. The most widely used technique in laboratory analysis of paint failures is the infrared spectrophotometry. The use of new Fourier transform infrared (FTIR) spectrophotometers permits much more versatility and precision than earlier instruments. The technique can identify the resin components of paints from the shapes and locations of their characteristic spectral peaks. It is highly desirable to separate the resin from the paint pigment before analysis, because the pigment may cause spectral interference. This is easy to do with thermoplastic but not thermosetting paints. Thermoplastic resins can be dissolved in solvents that are transparent in part or all of the infrared region, filtered to remove the pigment, and the solution placed in standard liquid cells or cast as films onto sodium chloride or other plates that are transparent in the infrared region. Thermosetting coatings can be pressed into potassium bromide pellets or their spectra measured using diffuse reflectance equipment. Although the pigment is not separated in these procedures, the spectrum of the pigment can often be separated from that of the total coating by the FTIR spectrometer. Spectra of field samples are compared against published standards or authentic samples. It should be remembered that exterior weathering may cause oxidation that may appear in spectral analyses.

 

3.6.4 OTHER SPECIALIZED INSTRUMENTATION. There are other specialized instruments that can be very helpful in failure analysis. These include emission spectroscopy, atomic absorption spectroscopy, and x-ray fluorescence instruments that identify and quantity the metals present in a coating. Their methods of operation are beyond the scope of this discussion.

 

3.7 FORMING CONCLUSIONS AND PREPARING REPORTS. Field and laboratory data should be analyzed logically and systematically to form conclusions as to the causes of paint failure. No data should be overlooked, and the conclusions should be consistent with the data. The report should include conclusions and recommendations requested by the activity for which the analysis was made. The report is perhaps the most important part of the failure analysis, because it presents the findings and conclusions of the investigation. No amount of good field or laboratory work will be useful unless it is presented well in the report. There must be a clear, systematic, and logical presentation of the findings, so that the conclusions are well supported. The report should not contain errors or otherwise be subject to challenge. Where conclusions are not firm, the extent of uncertainty should be stated.

 

4. EXPERT SYSTEM FOR FAILURE ANALYSIS. An expert system for failure analysis provides a systematic approach first to make a preliminary identification based on visual observations and then to verify it with supplementary information. The initial identification is based upon the answers to a series of questions designed to distinguish one type of failure from another. Decision trees 1 and 2 are used for this, one for surface defects and one for film failures. This same approach can be used in an expert system for a computer. The importance of a systematic approach cannot be overemphasized. One should be careful not to make permanent decisions on types and causes of failure until all the evidence is considered. The first step in the identification of a coating failure is to determine which decision tree to use. Tree l for cosmetic defects should be used if only surface damage is present, i.e., if the surface coat has not been completely penetrated to the underlying coat or structural substrate. Tree 2 for film failures should be used if coating damage has completely extended through the surface coat. After a preliminary decision of the type of failure has been made, look at the additional comments in the verification section below to obtain further support for this selection. If this information does not support the initial decision, reexamine the evidence or reconsider answers to the decision tree, until you are satisfied that you received the best overall answer. Remember, answers are not always easily obtained in failure analysis, and there may be multiple types and causes of failure. Thus, one may in some cases have to be content with the most probable cause or causes of coating failure.

 

4.1 COSMETIC DEFECTS. The following paragraphs further describe the cosmetic defects chosen in the initial decision.

 

4.1.1 CHALKING. Chalking occurs only on exterior surfaces, since it is caused by the sun’s ultraviolet rays. The loose chalk will be the same color as the coating, and, if it is severe, an undercoat may be visible. Chalking should not be confused with loose dirt which will not be the same color as the finish coat.

 

4.1.2 MILDEW. Mildew may resemble dirt but generally grows in discrete colonies rather than being uniformly distributed. In addition, it can be bleached with household bleach, but dirt cannot. Also, it can also be identified microscopically by its thread-like (hyphae) structures and its groups of spherical spores. Mildew is usually black in color but some microorganisms on coatings may have a green or red coloration.

 

4.1.3 DIRT. Dirt may be tightly or loosely held. It can normally be removed by washing with detergent solution. However, it may resist washing, if the dirt became embedded in the wet or soft paint.

 

4.1.4 UNEVEN GLOSS. Localized glossy spots may often be detected only if observed from a particular angle. They occur most frequently from spray application of heavy areas that do not penetrate into wood or concrete/masonry surface.

 

4.1.5 BLUSHING. Blushing is a defect from spraying fast-evaporating coatings, particularly lacquers such as vinyls and chlorinated rubbers, on hot, humid days. Condensation of moisture on the wet film dulls the finish to cause an opalescence.

 

4.1.6 BLEEDING. Bleeding occurs when solvent-containing coatings are applied to a bituminous coating or pavement. The stronger the solvent and the slower its evaporation, the greater will be the tendency to dissolve the bituminous material and cause it to bleed to the surface of the finish. New asphalt pavements or toppings should be allowed to remain 4 weeks before marking with paint to allow evaporation of volatile materials in the asphalt.

 

4.1.7 FADING. Fading of paint pigments occurs greatest in the sunlight. Thus, there will be less fading of coatings under eaves and other shaded areas. It also occurs more with synthetic organic pigments than with naturally-occurring mineral pigments (earth tones).

 

4.1.8 DISCOLORATION. Discoloration is caused by exposure of unstable pigments or resins to sunlight. Unstable resins like polymerized linseed oil may yellow. The only prevention is to use light-stable materials.

 

4.1.9 PIGMENT OVERLOAD. Pigment overload frequently results in a mottled appearance or a poor quality film. It can occur when attempting to tint a white paint to a deep tone. Latex paints are particularly susceptible to this problem. By specifying colors produced by the supplier, this problem can be avoided.

 

4.1.10 CHECKING. Early checking may be caused by improper formulation or application that causes the coating to shrink upon curing. Excessive thickness or rapid curing may be responsible. Aging will eventually cause checking of most coatings. It will often occur when existing paints are topcoated with more rigid finish coats that do not expand or contract as easily.

 

4.1.11 DRY SPRAY. Dry spray produces an uneven, pebbly finish with holidays. The holidays can be verified on a metal substrate with a holiday detector. It occurs most frequently when applying coatings with fast evaporating solvents on warm days or when the spray gun is held too far from the surface being painted.

 

4.1.12 SAGGING. Sags may not permit complete curing of the body of oil-based coatings and so may be soft below the surface. Reduced film thickness in the areas where the sagging initiated may be detected using a magnetic thickness gage on steel surfaces and by using a Tooke gage on other surfaces.

 

4.1.13 ORANGE PEEL. Orange peel is a defect of spray application. It usually is widespread, when it occurs, and is easily identified by its resemblance to the skin of an orange.

 

4.1.14 WRINKLING. Wrinkling occurs mostly with oil-based paints that are applied so thickly on hot days that the surface of the film cures rapidly to form a skin that does not permit oxygen to reach the interior of the film to cure it. The coating under the ridges is usually soft. Ridges generally occur in parallel rows.

 

4.2 FILM FAILURES. The following paragraphs further describe the film defects chosen in the initial decision.

 

4.2.1 CRAWLING. Crawling, sometimes called bug eyeing or fish eyeing, occurs during coating application, frequently on contaminated surfaces. It can usually be detected at the time of application. The smooth, oval shapes resembling eyes are characteristic of crawling.

 

4.2.2 ALLIGATORING. The characteristic checkered pattern of cracked coating will identify alligatoring. The coating is quite inflexible and cannot expand and contract with the substrate. It is a special form of cracking or checking.

 

4.2.3 INTERCOAT DELAMINATION. Intercoat delamination is simply the peeling of a stressed coat from an undercoat to which it is poorly bonded. It may occur in a variety of situations, but occurs frequently when a chemically curing coating such as an epoxy or a urethane has cured too hard to permit good bonding of a topcoat. It may also occur when coating a contaminated surface.

 

4.2.4 INTERCOAT BLISTERING. Intercoat blistering in a storage tank or other enclosed area is likely due to solvent entrapment. In water tanks or other areas exposed to water, the trapped solvent will cause water to be pulled into the blister. If the blisters are large, unbroken, and filled with water, it is sometimes possible to smell the retained solvent after breaking them. Intercoat blistering may lead to intercoat delamination.

 

4.2.5 PINPOINT RUSTING. Pinpoint rusting is frequently caused by applying a thin coating over a high profile steel surface. A thin coating can be verified using a magnetic thickness gage. It may also occur when steel is coated with a porous latex coating system. Pinpoint rusting may initiate corrosion undercutting of the coating.

 

4.2.6 CRACKING. Cracking is the splitting of a stressed film in either a relatively straight or curved line to an undercoat or the structural substrate. Cracking may occur from rapidly curing coatings such as amine-cured epoxies. Mudcracking is a more severe condition caused by rapid drying, particularly by heavily pigmented coatings such as inorganic zincs. It also occurs with latex coatings applied too thickly on hot days. On wood, too thick or too inflexible a film (usually a buildup of many layers) can cause cracking perpendicular to the grain of the wood.

 

4.2.7 BLISTERING TO SUBSTRATE. The blisters that arise from the substrate may be broken or unbroken. If broken, they may lead to peeling and be hard to identify. Blistering to wood or concrete/masonry substrates may be caused by moisture in the substrate.

 

4.2.8 PEELING. Peeling is the disbanding of stressed coatings from the substrate in sheets. It is generally preceded by cracking or blistering.

 

4.2.9 FLAKING (SCALING). Flaking or scaling is similar to peeling, except the coating is lost in smaller pieces. Flaking of aged alkyd coatings occurs commonly on wood.

 

4.3 EXAMPLES OF USING DECISION TREES. The decision trees 1 and 2 (Figures 1 and 25 can best be understood by using examples.

 

4.3.1 EXAMPLE OF SURFACE DEFECT. This example is a surface defect that does not penetrate the finish coat so that use of decision tree 1 is required. We start with Question 1, “Does detergent washing remove the defect?” In our example, the answer is “Yes,” so we proceed to Question 2, “Does wiping with a dry felt cloth remove defect?” This time the answer is “No,” so we proceed to Question 3, “Does defect disappear when treated with household bleach?” In our example, the answer is “Yes,” so we have tentatively identified the defect as “Answer 2” mildew.

 

4.3.2 EXAMPLE OF A FILM DEFECT. This example is a defect that penetrates the finish coat so that use of decision tree 2 is required. We start with Question 10, “Do oval voids that originate at time of coating application expose an undercoat or the structural substrate?” In our example, the answer is “No,” so we proceed to Question 11, “Does the failure expose only an undercoat?” This time the answer is “Yes,” so we proceed to Question 12, “Which best describes the failure?” In our example, the answer is “Peeling topcoat to expose undercoat,” so we have tentatively identified the defect as “Answer 17” intercoat delamination.

 

Figure 1

Decision Tree 1: Support for Analysis of Coating Failures

That Do Not Penetrate the Finish Coat

 

Figure 2

Decision Tree 2: Support for Analysis of Coating Defects

That Penetrate the Finish Coat

 

5.  PROGRAMMING MAINTENANCE PAINTING.

 

5.1 DEFINITIONS OF PROGRAMMED PAINTING AND MAINTENANCE

PAINTING. Paint programming is a systematic planning process for establishing when painting is required, what painting should be done, by whom, at what times, and in what manner. Maintenance painting is a vital adjunct to programmed painting. It is defined as a field procedure for maintaining existing coatings in an acceptable condition.

 

5.2 COMPONENTS OF PROGRAMMED PAINTING. There are three basic components of successful paint-programming plans: plans for initial design of the facility, plans for monitoring conditions of structures and coating systems, and plans for maintenance painting. Each plan must be prepared properly and completely for the total program to be successful. Programmed painting can best be implemented as a computer program. This program will contain the initial design data, data on the conditions of the structures and their coating systems obtained from an annual inspection report, and recommended maintenance painting schedules and procedures. The latter should include cost estimates for each item of work so that funding can be requested well in advance of the time it will be spent. Cost estimating programs for construction work are available in the Construction Criteria Base (CCB) (National Institute of Building Sciences, Washington, DC) and proprietary sources.

 

5.2.1 INITIAL DESIGN. The design of both new structures and their coating systems is critical to achieving maximum life of each.

 

5.2.1.1 STRUCTURAL DESIGN. Structures should be designed so that they are easy to coat initially and to maintain in an acceptable condition. Common structural design defects include:

 

a) Contact of Dissimilar Metals. The more active metal will rapidly be consumed by galvanic corrosion to protect the less active metal. This includes contact of steel and stainless steel.

 

b) Water Traps. Structural components that collect rainwater corrode more rapidly. These components should either be turned upside down or have weep holes of sufficient size and correct placement drilled in them. Weep holes should be as large

as possible and placed at the bottom of the structure.

 

c) Configurations That Permit Vapors or Liquids to Impinge on Structural Components. Structures such as steam lines.

 

d) Configurations Restricting Access. Structures that restrict access for painting receive poor quality maintenance.

 

e) Designs Creating Crevices. Crevices are difficult to coat, and the oxygen deficiencies in them produce a type of galvanic corrosion.

 

f) Other Difficult to Paint Surfaces. Sharp edges and welds should be ground, pits should be filled, and corners should be avoided.

 

5.2.1.2 DESIGN OF COATING SYSTEM. The original coating system must be designed to be compatible with both the environment in which it is to be located and the substrate to which it is to be applied.  As far as possible, it is desirable to specify coating systems that are easy to apply and maintain. It is always preferable to do the surface preparation and the paint application in the controlled environment of a shop as compared to the field. If this is not possible, this work should be accomplished at the work site before rather than after erection.

 

5.2.2 PLAN FOR MONITORING CONDITIONS OF STRUCTURES AND THEIR

PROTECTIVE COATINGS. Annually, each coated structure at each activity should be inspected for deterioration of both the substrates and their coatings. Both the types and the extent of deterioration should be noted, and the generic type of the finish coat should be determined if it not already known. An estimate should also be made as to when structural and coating repairs should be made to prevent more serious damage. Other structures at the activity that require the same type of maintenance should also be noted, since it would be more economical to include as many structures as appropriate in a single contract. An example of an inspection form which has been successfully used for routine inspections and could be modified to meet an installation’s needs is shown in Figure 3.

 

5.2.2.1 DETERMINING THE TYPE OF COATING FAILURE. The type of coating failure can be determined by following the procedure described.

 

5.2.2.2 DETERMINING THE EXTENT OF COATING FAILURE. In maintenance painting, it is necessary to determine the extent of coating failure to permit realistic bidding for the repair work. To do this, both the severity of the deterioration and its distribution must be defined. The level of severity will indicate whether only the finish coat or other coats are involved in the deterioration and how it can best be repaired. If the distribution is limited, spot repairing is likely to be practical; if it is extensive, it is probably best to remove all the coating and repaint. Standard block diagrams for estimating coating deterioration on ships for “Overall Extent” and “Extent Within Affected Areas” are generally also appropriate for shore structures. They are described in ASTM F 1130. First, draw an imaginary line enclosing all deterioration and select the standard “Overall Extent” diagram that best matches the imaginary area. Then, select the standard “Extent Within Affected Area” diagram that best matches the areas within the imaginary line. The number and letter of the selected diagrams establish the extent of deterioration. Whatever system is used to determine the extent of deterioration, it should utilize a standard format so that evaluations of different structures can be compared and priorities can be established. It is also important in maintenance painting to determine precisely the amount of loose and peeling paint to establish the amount of work to be done. This will eliminate any controversy over a “site variation,” i.e., the contractor claiming that there was much more work necessary than described in the specification. It is a standard practice to define “loose and peeling paint” as that paint that is easily removed with a dull putty knife.

 

5.2.2.3 DETERMINING THE GENERIC TYPE OF THE FINISH COAT. Once a painting program is set up, the identifications of paints being applied will automatically be entered into the database. If the generic type of the finish coat is not known, it can be determined by infrared spectrophotometric analysis. The general compatibility of a coating can be determined by the solvent rub test.

 

5.2.3 TYPES OF MAINTENANCE PAINTING. In planning maintenance painting, it is first necessary to determine the general scope of the work. There are four different approaches to maintaining an existing coating in an acceptable condition:

 

a) Cleaning only to restore to an acceptable condition. This may be accomplished by pressure washing or steam cleaning.

 

b) Spot repair (priming and topcoating) of areas with localized damage but otherwise sound paint. This should be done before the damage becomes more extensive.

 

c) Localized spot repair plus complete refinishing with topcoat only. This should be done when localized repair only would produce an unacceptable patchy finish.

 

d) Complete removal of existing paint and total repainting. This should be done when the damage is so extensive that types “b” or “c” are impractical or uneconomical.

 

Figure 3

Coating Condition and Identification Form

 

Repair of exterior coatings may not be warranted with the first appearance of weathering, but deterioration should not proceed to the point that damage occurs to the substrate, or more costly surface preparation or application techniques become necessary. If lead-containing paint is present, the costs for paint repair or removal will be much more expensive. If the paint can be maintained in place, a great deal of savings will result. New restrictions on abrasive blasting and other surface preparation techniques may also significantly increase total costs. Thus, scheduling of repairs should be made to avoid such costly operations.

 

5.2.4 PLAN FOR MAINTENANCE PAINTING. The plan for maintenance painting includes selection of the surface preparation, application, and inspection methods and the materials to be used.

 

5.2.4.1 SELECTING MATERIALS FOR MAINTENANCE PAINTING. For localized repairs to an otherwise sound coating system (types “b” and “c”), it is wise to repair a damaged coating system with the same coating previously used or one of the same generic type or curing mechanism to avoid incompatibility. If in doubt as to the compatibility of a paint to be applied to an existing finish, apply a small patch to it and inspect it after 2 to 3 days for any bleeding, disbanding, or other sign of incompatibility. For total recoating (type “d”), select the coating as described for new work.

 

5.2.4.2 SURFACE PREPARATION FOR MAINTENANCE PAINTING. For making localized repairs, it is best to use the surface preparation methods for different substrates described. It may be more practical or necessary, however, to use hand or power tools rather than abrasive blasting where the amount of work to be done is small, or where abrasive blasting would contaminate an area. Loose and peeling coating should be removed, and the adjacent intact coating should be sanded to produce a feathered edge and roughened paint surface extending 2 inches beyond the repair area. The feathered edge will produce a smoother transition between the old and new paint and roughening the adjacent intact paint will permit good adhesion of the new primer. Feather edging of steel may be accomplished by blasting with a fine abrasive (e.g., 60 mesh grit or finer) with the nozzle held at a low angle about 3 or 4 feet from the surface.

However, even fine abrasive may damage adjacent coating. Thus, it is best to determine if there are any adverse effects with a surface preparation procedure before proceeding will it.

 

5.2.4.3 APPLICATION FOR MAINTENANCE PAINTING. Spot application of paint in maintenance painting is usually done by brush or spray, as the painter determines to be most efficient. Brushing of the primer is usually preferred where the surface is rough or otherwise difficult to paint. Patches should be extended 2 inches beyond the areas of damaged coatings where the adjacent intact paint has been previously roughened.

 

5.2.4.4 INSPECTION OF MAINTENANCE PAINTING. Inspection of maintenance painting usually consists of visual inspection for workmanship, dry film thickness, and adhesion. Fuel tanks and lines, waterfront structures, and other critical structures should also be tested for holidays Imperfections in the coating).

 

5.2.5 SCHEDULING THE WORK. By planning work well in advance, it is possible to schedule it at a time when minimum inclement weather is expected. It may also be possible to schedule it when there will be less interference with other trades doing construction work or personnel utilizing the structures.

 

 

CHAPTER 4

INSPECTION OF PAINTING OPERATIONS

 

1. INSPECTION OF PAINTING OPERATIONS

 

1.1 SCOPE. This section describes the duties of an inspector, general inspection procedures, and specific inspection methods used in inspecting painting operations. Depending upon the job and the contract requirements, quality control inspectors may be contractor-supplied (that is, contractor quality control - CQC) or Owner personnel. In either case, the contracting officer

 

NOTE: Construction contract terminology is variable.  In this publication the term “contracting officer” refers to the Owner’s representative for the project who has contractual authority over execution of the construction contract.

 

is responsible for ensuring the quality of the job. The intent of this section is to describe proper inspection procedures so that Owner personnel will know either how to inspect a painting operation or to ensure that someone else has done it correctly.

 

1.2 IMPORTANCE OF INSPECTION. The success of a painting job depends upon the specification requirements being met for surface preparation, application and materials. Most coating failures are the result of contract requirements not being met. Inspection procedures are designed to detect situations when the requirements of the contract are not being met. Thus, inspection is a key factor in obtaining the performance and durability built into the specification.

 

1.3 CONTRACTOR QUALITY CONTROL INSPECTION. In Owner painting, quality control inspection is often provided by the contractor. For large jobs, a contractor usually hires an inspector. For smaller jobs (less than $200,000), a contractor's superintendent may carry out the quality control inspection. If deemed necessary because of the size or difficulty of a job, or because of the crucial function of a structure, the contract specification can require the contractor to hire a certified inspector (e.g., NACE has a certification program). In this way, the contractor's inspector may be more independent of the contractor and may have better inspection skills. Although this requirement may increase inspection costs, the increased cost of proper inspection as opposed to none or poor inspection has been found by the private sector to be cost effective. Quality control inspectors should report deviances from the contract specification in writing to the contracting officer. Appropriate Owner action in response to these reports is essential in obtaining the quality of the job built into the specification.

 

1.4 DUTIES OF AN INSPECTOR. The duties of an inspector include understanding the contract specification requirements, making sure that the specification requirements are met by the contractor, and keeping good records. Record keeping is a very important part of inspection. It should occur during all phases of the job. Records form an important part of the permanent record on each building, and provide key information in the case of contract disputes.

 

1.4.1 RECORD KEEPING. Inspectors should keep records in a bound book (logbook). Each page should be initialed by the inspector and dated. The record book should contain:

 

·         Written records of verbal agreements made between the contracting officer or the inspector and the contractor.

·         Daily descriptions of the type of equipment and number of workers on the job site.

·         Descriptions of the coating materials that are on site.

·         Records of the rate of work progression. e) Measurements of ambient conditions.

·         Results and observations of the surface preparation inspection.

·         Measurements and observations of coating application, including time between surface preparation and coating application, and times between coats.

·         Results of the final and warranty acceptance inspections.

 

It is especially important that agreements between the contracting officer (or designee) and the contractor that modify the contract specification be in writing and be signed to minimize future disputes.

 

1.5 INSPECTION EQUIPMENT. A description of equipment used in typical inspections  is summarized in Table 1. Instructions on its use are provided in the equipment manufacturer's literature. Some of the equipment is readily available from local hardware or variety stores but some is specialized equipment for painting operations. Suppliers of specialized equipment are listed in:

 

·         ASTM, 1916 Race Street, Philadelphia, PA 19103.

·         NACE, P.O. Box 218340, Houston, TX 77218.

·         SSPC, 516 Henry Street, Suit 301, Pittsburgh, PA 15213-3738.

·         Paul N. Gardner Company, Inc., Gardner Building, P.O. Box 10688, Pompano Beach, FL 33060-6688.

·         KTA-TATOR, Inc., 115 Technology Drive, Pittsburgh, PA 15275.

·         ZORELCO, P.O. Box 25500, Cleveland, OH 44125.

·         Pacific Scientific, 2431 Linden Lane, Silver Spring, MD 20910.

·         S. G. Pinney & Associates, 2500 S.E. Midport Road, P.O. Box 9220, Port St. Luice, FL 34952.

 

1.6 INSPECTION STEPS. The inspector's tasks can be divided into eight general steps, which are summarized in Table 2 and discussed in more detail below. Special equipment required in each of these steps is also listed in the table. A form that may be useful in reviewing the contract is provided in Figure 1, and one for organizing inspection data is provided in Figure 2.

 

1.6.1 REVIEW SPECIFICATION AND CORRECT DEFICIENCIES, If Any. The first part of any inspector's job is to read and understand the contract specification. If deficiencies are found, resolution of the deficiencies between the contracting officer and the contractor is needed prior to start of work. Any changes in the contract specification must be documented in writing and signed by the two parties or their representatives. Copies of these agreements should be kept in the inspector's records. In addition to reviewing the specification, the inspector must also review the contract submittal. The form shown in Figure 1 may help an inspector to identify key specification requirements and essential information from the submittals, and to prepare for the preconstruction conference. Note that at this time, all the information needed to complete the form may not be available. However, the information should be available before the start of the job.

 

1.6.2 VISIT JOB SITE. It is important for the contractor to visit the job site with an inspector prior to the preconstruction conference so that the scope of the job and any constraints are understood. Potential problems that are found, such as difficulty with access to the job site, can then be resolved at the preconstruction conference. Such visits have been shown to be effective in reducing problems during the job.

 

Table 1

Equipment for inspecting painting operations

 

Table 2

Inspection steps

 

Figure 1

Sample inspector’s contract summary form

 

Figure 2

Sample daily project reports for painting inspectors

 

1.6.3 CONDUCT PRE-CONSTRUCTION CONFERENCE. At the beginning of each new contract or work order before the start of any surface preparation or coating application, a meeting should be held with the contractor, contracting officer, inspector, and

other key people. Figure 1 may be helpful in this discussion. During this conference, agreement should be reached on details of the specification and the procedures and expectations of the inspector. For example, the number and locations for inspecting surface preparation and coating thickness should be determined. Scheduling, job sequencing, job stops for inspection, and other job-related issues should be discussed. Differences between contractor and contracting officer should be resolved at this time to avoid future misunderstandings and job delays. Agreements that result in a change of the contract should be made in writing, signed and included in the record book.

 

1.6.4 INSPECT JOB SITE AFTER PRE-SURFACE PREPARATION. Prior to surface preparation or coating application, it is necessary to be certain that requirements in the specification relating to readying a surface or area for painting are carried out. These may include protecting adjoining surfaces, removing weld splatter, ensuring that surfaces are free of oil and grease, grinding sharp metal edges, protecting plants and other shrubbery, replacing rotted wood, caulking joints, and the like.

 

1.6.5 INSPECT COATING MATERIALS. Coating materials must be inspected at the job site to identify deficiencies that could result in failure of the paint film. The following checklist can be used:

 

·         Read labels on the coatings to verify that the coatings are the ones specified or approved.

·         Take one representative 1-quart sample in accordance with the specification. Retain the sample for a period of 1 year from the date of final approval of the contract work in case of coating film failures or contract disputes.

·         Ensure that coating materials are in sealed, unbroken containers that plainly show that the date of manufacture is within 1 year. The label should display the manufacturer's name, specification number/or designated name, batch number, and FED-STD-595 color.

·         Inspect the paint after stirring for homogeneity, weight, viscosity, color, and smell. If deficiencies are suspected from these tests, the paint should be sent to a laboratory for testing.

·         Count the cans of paint on the job site to determine that a sufficient quantity is available to complete the job as specified. For multi-component paints, confirm that the proper ratio of materials for each specific coating is present. To estimate the paint required for a job, use the nomograph  shown in Figure 3.

·         Ensure that the paint is stored on site in an approved building or area.

·         Record number of cans and paint condition in record book.

1.6.6 MEASURE AMBIENT CONDITIONS. Most coating systems will not dry or cure properly under extremes of temperature or humidity, nor will they adhere well if applied over damp surfaces. For example, specifications often require that the substrate surface temperature be 5 degrees F above the dew point and rising. For these reasons painting contracts have requirements for air and surface temperature, dew point, and, perhaps, additional environmental conditions. The paint manufacturer's technical data sheet will also have limits for acceptable environmental conditions. (If the limits are in conflict, agreement on the limits should be reached during the preconstruction conference.) Because temperature and dew point may vary considerably within a small area, temperature and dew point should be measured in the immediate vicinity of the work being done. Surfaces being painted may be colder than the atmospheric temperature and their temperatures should be measured in addition to atmospheric temperatures. Dew point at the surface being painted may also be different from that in the air away from the surface. Thus, dew point should be measured near the surface. Ambient condition measurements should be made about every 4 hours. These times should include before start of job, after breaks, and after sudden changes in environmental conditions. Sudden changes in environmental conditions should also be recorded in the logbook. In addition, do not paint in rain, snow, fog, or mist, or when the surface is covered with frost.

Figure 3

Nomograph for estimating quantities of paint required for a job

 

1.6.6.1 RELATIVE HUMIDITY AND DEW POINT. These conditions are measured using a psychrometer. Most psychrometers consist of a wet bulb thermometer, a dry bulb thermometer, and a standard psychometric table. Using the table, the relative humidity is obtained from the two temperature readings.

 

1.6.6.2 SURFACE TEMPERATURE. Surface temperature is measured using a special thermometer in which the temperature sensing element is designed to come into intimate contact with the surface and to be shielded from the surrounding air. The surface temperature of the coldest and warmest surfaces should be within the limits of the specification. The location, temperature and time of the measurement should be recorded in the record book.

 

1.6.7 INSPECT SURFACE PREPARATION. Surface preparation inspection procedures include inspecting equipment, and associated materials (e.g., blasting medium and chemicals), as well as the cleaned surface itself. Proper surface preparation, as described in the specification, must be completed to obtain a durable coating film.. Many of the surface preparation requirements involve visual inspection of the surface, and some are subjective. For example, the specification may require removal of loose paint (for example, paint that can be removed by a dull putty knife), removal of surface chalk to some specified level and feathering of edges on the remaining paint film. To help avoid conflicts between the contractor and the inspector, it may be useful to have the contractor prepare a test surface about 4 by 4 feet that can then be used as a standard for surface preparation. Photographs of the test surface could be part of the inspection record. For steel, the test surface should be protected by a clear coating. When blast cleaning is part of the surface preparation, it should be performed in a manner so that no damage is done to partially or entirely completed portions of the work, adjacent surfaces, or equipment. Usually blast cleaning should progress from the top towards the bottom of a structure, should be carried on downwind from any recently painted structures, and should not scatter abrasive on or into surrounding buildings or equipment. All dust from blasting operations must be removed by brushing, blowing, or vacuuming before painting.

 

1.6.7.1 ABRASIVE-BLASTING SURFACE PREPARATION EQUIPMENT AND SUPPLIES

 

1.6.7.1.1 AIR CLEANLINESS. Routinely (at least two times a day or every 4 hours) inspect air supply lines for both blast cleaning or paint spray application to ensure that the air supply is clean and dry. A blotter test as described in ASTM D 4285 can be used to determine whether the air supply is free of oil and moisture. In this test, a clean white blotter is held downstream about 19 inches from the nozzle for 2 minutes. It should remain clean and dry.

 

1.6.7.1.2 ABRASIVE. Each batch or shipment of abrasive should be checked for oil contamination and, if required, soluble salts. Either can contaminate a cleaned surface and reduce the service life of the coating. A commonly used test to check for oil contamination is to take a small random sample of the abrasive, place it together with clean water in a small bottle or vial, shake the bottle for a minute and examine the surface of the water. There should be no sheen of oil on the surface of the water. Soluble ionic contaminants can be detected using the electrical conductivity test described in ASTM D 4940. In addition, the abrasive should feel dry to the touch when it is placed in the abrasive blasting machine. Recycled abrasives break down after several cycles, and the number of cycles depend upon the type of the abrasive. The abrasive should be replaced when it no longer meets the requirements of the specification.

 

1.6.7.1.3  BLAST HOSES AND NOZZLES. Blast hoses should be in good condition and kept as short as possible. The nozzle pressure and diameter of the nozzle orifice both affect the cleaning rate. A nozzle orifice gage is used to determine the orifice size. Air pressure at the nozzle is measured using a hypodermic needle air pressure gage and should be from 90 to 100 psi for optimum efficiency. Usually these parameters are measured at the start of a job and when production rates are decreasing. An increase of nozzle size of more than 1/8-inch causes loss of cleaning efficiency because of the increased pressure drop. Increased nozzle size also causes increased use of abrasive. Profile should be inspected when major changes in cleaning efficiency are noted.

 

1.6.7.1.4 SAFETY. Special safety precautions are required during abrasive blasting. Refer to Section 13 for more information. These precautions include use of external couplings on blast hoses and dead man controls, and electrical grounding of equipment.

 

1.6.7.2 WATER BLASTING. Since contaminants, such as salts and oils, in the blasting water will be left behind on the blast cleaned surface and may adversely affect the adhesion of the coating to be applied, water should be essentially free of contaminants. If cleaning agents are added to the water used for blasting and cleaning, the surfaces must be thoroughly rinsed with clear water. An exception is the use of flash-rusting control agents when cleaning steel. These agents should only be used in accordance with the contract specification and the coating manufacturer's recommendations. As for abrasive blasting, hoses should be in good condition and kept as short as possible. Special safety precautions, similar to those used in abrasive-blast cleaning, also need to be taken. In addition, consideration should be given to the slipperiness of wet

surfaces.

 

1.6.7.3 FREQUENCY OF INSPECTING CLEANED SURFACES. The objective of the inspection is to ensure that the entire surface was prepared in accordance with the specification. The inspection report should provide a representative description of the cleaned surface. The specific number and location of places at which surfaces should be inspected must be in accordance with the contract specification. If not detailed in the specification, SSPC PA 2 can be used as a guide. Additional inspection sites that should be considered include those where the existing paint was failing, in hard-to-reach areas where surface preparation is difficult, and where major changes in equipment were made.

 

1.6.7.4 INSPECTING PREPARED STEEL SURFACES.

 

1.6.7.4.1 CLEANLINESS. If a small representative sample of surface was not prepared to use as the standard for surface preparation, the degree of blast or tool cleaning should be compared to the description given in the SSPC or NACE specification referred to in the contract specification. The appearance should correspond with the specified pictorial standards of SSPC VIS 1, SSPC VIS 3, or a NACE panel. After blasting, blast-cleaned surfaces must be cleaned (e.g., vacuum, air blast, or brushing) to remove traces of blast products from the surface or pitted areas. One of two tests for cleanliness can be used. In one, a white glove or other clean cloth is rubbed over the surface and examined for soiling or debris, and in the other, a piece of clear adhesive tape is applied to the surface, removed and the adhesive side examined for debris.

 

1.6.7.4.2 PROFILE. Profile is measured using one of three pieces of equipment: comparator, depth micrometer, or replica tape. It should be noted that the three techniques may give slightly different results. Complete descriptions of standard methods for each of these techniques are described in ASTM D 4417, Field Measurement of Surface Profile of Blast Cleaned Steel.

 

1.6.7.5 INSPECTING CONCRETE, MASONRY, WOOD, PLASTER, WALLBOARD, OLD PAINT. On these surfaces, specifications may have requirements for measurements of moisture content and residual chalk, as well as visual condition. The specification should state how moisture is to be measured, since the different methods provide different types of data. Moisture content can be measured either using a plastic sheet test (ASTM D 4263) or an electric moisture meter. In the plastic sheet test, a piece of plastic film is taped (all edges) to the surface. After 24 hours, the film is removed and the underside is examined for the presence of condensed water. Prior to application of most coatings, the sheet should be free of condensed water. This is because accumulation of water at the concrete/primer interface will usually lead to delamination of the primer. To use a moisture meter on hard surfaces, small holes must drilled for the electrodes. These holes should be repaired after the measurements are completed. The contract should state a moisture requirement. Residual chalk is usually measured using a piece of cloth of contrasting color, in accordance with ASTM D 4214. Other procedures are also described in ASTM D 4214. In the cloth method, a piece of cloth is wrapped around the index finger, placed against the surface and then rotated 180 degrees. The spot of chalk on the fabric is compared with a photographic reference standard. Chalk readings of 8 or more indicate adequate chalk removal providing reasonable assurance that the new coating should not fail because of application to a chalky surface.

 

1.6.8 INSPECT COATING APPLICATION. Proper application is another essential factor in determining paint performance, and the requirements of the specification must be followed. General guidance on paint application is presented in Section 7 and SSPC PA-1. Inspectors should assess ambient conditions, application equipment, ventilation, mixing, film thickness, and drying and curing conditions to ensure that they are within the limits of the specification and the technical data sheets for the paints. It is especially important that the paints be applied and cure within the temperature and relative humidity limits of the specification, since these conditions affect film formation. A properly dried and cured film is essential for satisfactory paint performance, and deviations from these limits may prevent proper film formation. For two-component systems, the inspector should ensure that the materials were mixed together and in the proper ratio. For all materials, thinning should only be allowed in accordance with the manufacturer's data sheet.

 

1.6.8.1 APPLICATION EQUIPMENT. Equipment to apply the coating must be in acceptable working condition. When spraying, the spray pattern should be oval and uniform, the gun should be held at the proper angle and distance from the surface, and each spray pass should overlap the previous one by 50 percent. Proper techniques should also be used for brushing, rolling, or other application procedures. Refer to Section 6.

 

1.6.8.2 VENTILATION. The ventilation of tanks and other enclosed areas where paint is to be applied and cured must meet the requirements of OSHA's Confined Space Regulation, and the contractor's safety plan required by contract specification. Good ventilation is also necessary for proper coating cure.

 

1.6.8.3 MIXING/THINNING. Paints must be properly mixed. Paint solids often settle out during storage and must be completely blended into the paint vehicle, resulting in homogeneous mixture. For multi-component paints, the inspector should ensure that all components have been mixed in the proper proportion, that the mixing is thorough and that the resulting paint is uniform in appearance. Required induction times must also be met to obtain satisfactory application and film properties. Although the paint manufacturer prepares paint to produce a consistency for brushing, rolling, or spraying, sometimes additional thinning is permitted in the specification. Thinning of the paint must follow manufacturer's instructions for both type and amount of solvent. A thinned paint will cover more surface area but the dry film thickness will be less and may not

meet the requirements of the specification.

 

1.6.8.4 FILM THICKNESS. Contract specifications may require a minimum and/or a maximum dry film thickness for each coating application. Wet film thickness measurements made at the time of paint application are used to estimate dry film thickness so that appropriate adjustments in the application procedure can be made

to meet the specification. Wet film thicknesses are not used in meeting contract requirements because of the many factors (solvent evaporation, wetting energies) that affect the measurement. Procedures for making wet film thickness are described in ASTM D 4414, Wet Film Thickness by Notch Gages. The dry film thickness is estimated from the wet film thickness according to:

 

·         Dry Film Thickness = Wet Film Thickness x Percent Volume Solids

 

The percent volume solids is available from the coating manufacturer's data and should be part of the inspector's records. Dry film measurements are made after the coating has hardened. For steel surfaces, thickness measurements can be made according to SSPC PA 2 or ASTM D 1186 or ASTM D 1400, Nondestructive Measurement of Dry Film Thickness of Nonconductive Coatings Applied to a Nonferrous Metal Base. (There are some differences in calibration procedures between SSPC PA 2 and the ASTM standards. If the contract specification does not specify the exact procedures to be used, the procedures should be agreed upon, and the agreement documented, during the preconstruction conference.) ASTM D 4128, Identification of Organic Compounds in Water by Combined Gas Chromatography and Electron Impact Mass Spectrometry describes a destructive procedure for measuring coating thickness on non-metallic substrates using a Tooke gage. If the contract specification requires minimum film thicknesses for each layer, the measurements must be made after each layer has cured, taking care not to depress soft coatings during measurements.

 

1.6.8.5 DRYING. The inspector should ensure that a previous coat has dried or cured as required by the contract specification before another coat is applied. For most thermosetting coatings, manufacturers specify a maximum, as well as a minimum, curing time before application of the next coat. In some situations, a coating manufacturer may require use of a methyl ethyl ketone (MEK) rub test to assess curing prior to application of another layer. The inspector's record should provide information so that the dry/cure time for each layer can be determined.

 

1.6.9 FINAL APPROVAL PROCEDURES. The final approval inspection is very important since it determines whether the contract requirements have been met, and whether identified deficiencies have been corrected. Since most coatings function as a barrier and since the protection of a surface is usually directly related to coating thickness and continuity, inspection of coating thickness and film continuity are essential. The following checklist can be used to inspect the final job:

 

1.6.9.1 EXAMINE, as required by the specification, the cured coating system for visual defects, such as runs, sags, blistering, orange peel, spray contaminants, mechanical damage, color and gloss uniformity, and incomplete coverage. Note any areas of rusting, or other evidence of premature failure of the coating system.

 

1.6.9.2  IF DEFECTS ARE OBSERVED, bring them to the attention of the contractor for correction. If resolution of the corrective action cannot be reached with the contractor, bring the matter to the attention of the contracting officer. Dated photographs of the defects could become part of the inspector's records, if deemed appropriate.

 

1.6.9.3 MEASURE AND RECORD the total dry film thickness using appropriate gages. Wh en the Tooke gage is used, the coating must later be repaired.

 

1.6.9.4 MEASURE ADHESION as required in the contract specification. Adhesion measurements vary from those made with a knife (ASTM D 3359, Measuring Adhesion by Tape) to those that determine the amount of force needed to remove a dolly (ASTM D 4541, Pull-Off Strength of Coatings Using Portable Adhesion Testers) that has been cemented to the surface.

 

1.6.9.5 EXAMINE THE COATINGS on steel structures for pinholes using a holiday detector as described in NACE RP0188, if required in the contract specification.

 

1.6.9.6 RECORD THE RESULTS of observations in the record book. Document photographs taken and retain in the record book.

 

1.6.10 YEAR WARRANTY INSPECTION. The warranty inspection includes a visual inspection of the film, and may involve a chalk, film thickness, and adhesion measurements. Since the film was found to be essentially free of defects upon completion of the job, a goal of the inspection is to identify contractually unacceptable defects that have formed during the course of the year. Resolution of film deficiencies should follow the same steps as for the final inspection. Deficiencies should be recorded in the logbook. Documented photographs (date, location, and photographer) should be included if deemed necessary to resolve contract disputes.

 

2.  FIELD INSPECTION INSTRUMENTS

 

2.1 INTRODUCTION. This section describes field instruments commonly used in inspection of field painting.  For equipment descriptions having no referenced standards, no standards are available. Typical suppliers include:

 

·         Paul N. Gardner Company, Inc., Gardner Building, P.O. Box 10688, Pompano Beach, FL 33060-6688.

 

·         KTA-TATOR, Inc., 115 Technology Drive, Pittsburgh, PA 15275.

 

·         ZORELCO, P.O. Box 25500, Cleveland, OH 44125.

 

·         Pacific Scientific, 2431 Linden Lane, Silver Spring, MD 20910.

 

·         S. G. Pinney & Associates, 2500 S.E. Midport Road, P.O. Box 9220, Port St. Luice, FL 34952.

 

2.2 ILLUMINATED MICROSCOPE. A pocket-sized illuminated microscope is frequently used to detect mill scale, other surface contamination, pinholes, fine blisters, and other microscopic conditions during painting operations. These microscopes are available with magnifications of 5 and higher.

 

2.3 INSTRUMENTS FOR USE WITH ABRASIVE BLASTING. A few instruments are available for testing the operational readiness of equipment for abrasive blasting of metals for painting.

 

2.3.1 GAGE FOR DETERMINING NOZZLE PRESSURE. A pocket-sized pressure gage with a hypodermic needle is used to determine the blasting pressure at the nozzle. The needle is inserted in the blasting hose just before the nozzle in the direction of the flow. Instant readings can be made up to 160 pounds per square inch (gage) (psig).

 

2.3.2 WEDGE FOR DETERMINING DIAMETER OF NOZZLE ORIFICE. A hand-held calibrated wedge is inserted in the direction of flow into the nozzle orifice to determine its size (inches) and airflow (cfm at 100 psig). The orifice measuring range is 1/4 to 5/8 inch, and the airflow range is 81 to 548 cfm.

 

2.3.3 SURFACE CONTAMINATION DETECTION KIT. The level of cleanliness of abrasive blast cleaned steel can be determined by comparing it with SSPC VIS 1 photographic standards. SSPC VIS 3 photographic standards are used for determining level of cleanliness of hand-cleaned steel and power-tool cleaned steel. Standard coupons of steel blasted to different levels of cleanliness are also available for comparison from NACE, and procedures for their use are given in NACE TM0170. Test kits for detection of chloride, sulfate, and ferrous ions, as well as pH, are commercially available. They contain strips, swabs, papers, and operating instructions for simple chemical testing.

 

2.3.4 PROFILE OF BLASTED STEEL. There are three methods for determining the profile (maximum peak-to-valley height) of blasted steel surfaces described in ASTM D 4417.

 

2.3.4.1 COMPARATORS. Several types of comparators are available for determining surface profile. These include ISO, Clemtex, and Keene-Tator comparators. Basically, they use a 5-power illuminated magnifier to permit visual comparison of the blast-cleaned surface to standard profile depths. Standards are available for sand, grit, and shot-blasted steel.

 

2.3.4.2 SURFACE PROFILE GAGES. A surface profile gage is an easy instrument to use to determine surface profile, but 10 to 20 measurements must be averaged to obtain reliable results. The gage consists of an instrument with a flat base that rests on the profile peaks and a tip that projects into the valleys. The tip can be blunted by dragging it across steel surfaces. This prevents the tip from reaching the bottom of the valleys in the profile, resulting in a profile value that is less than the correct value.

 

2.3.4.3 TESTEX PRESS-O-FILM REPLICATE TAPE. Testex Press-O-Film replicate tape produces the most precise profile measurements, according to the precision statement of ASTM D 4417. The tape consists of a layer of deformable plastic bonded to a polyester backing. The tape is rubbed onto the blast-cleaned surface with a plastic swizzle stick to produce a reverse replicate of the profile. The tape profile is then measured with a spring micrometer. The micrometer can be set to automatically subtract the 2-mil non-deformable polyester backing. After measurements, the tapes can be stored as records of profile heights.

 

2.3.5 THERMOMETERS. Several different types of thermometer and temperature recorders are available for field use. They are used to measure ambient temperatures, surface temperatures of steel, and temperatures of wet paints.

 

2.3.6 PSYCHROMETERS. Several different manual or battery-powered psychrometers are available for measuring air temperatures, relative humidity, and dew point. In most cases, two glass thermometers are used with the instrument, as described in ASTM E 667, Clinical Thermometers (Maximum Self-Registering, Mercury-in-Glass). One thermometer has a clean "sock" or "wick" on it that is wetted with water. Air is circulated around the thermometers by the motorized fan or by whirling the hand-held sling psychrometer. Whirling should be with a steady, medium speed. Both thermometers should be read periodically and the airflow (whirling) continued until the reading becomes constant. The "wet" bulb thermometer temperature will be lowered by evaporation of the water on the sock. The evaporation rate is related to the relative humidity and barometric pressure. Psychrometric tables relate temperature depression (difference between "dry" and "wet" bulb readings) to relative humidity and dew point. These standard tables, available from suppliers of psychrometers, cover the range from 23.0 to 30.0 inches barometric pressure. The effect of barometric pressure is relatively small; if it is unknown, use the 30.0-inch pressure table near sea level and the 29.0-inch pressure table at high elevations.

 

2.3.7 WIND METER. A pocket-size wind meter is available for determining wind speed in miles per hour and velocity of air moving across a spray booth. Spraying on days with excessive winds can cause overspray or dry spray problems.

 

2.3.8 MOISTURE METER. Meters are available for determining the moisture content of wood, plaster, concrete, or other materials. Some are nondestructive, while others require contact pins to be driven into the surface. An alternate non-destructive procedure for determining if too much moisture is present in cementitious surfaces is described in ASTM D 4263.

 

2.3.9 WET FILM GAGE. Gages for determining paint wet film thickness are available in different types, two of which are described in ASTM D 1212 and one in ASTM D 4414. All are destructive in that they disturb the paint and require touching up the film.

 

2.3.9.1 NOTCHED METAL GAGE. The most widely used type of wet film thickness gage, described in ASTM D 4414, consists of a thin rigid metal notched gage, usually with four working faces. Each of the notches in each working face is cut progressively deeper in graduated steps. The gage with the scale that encompasses the specified thickness is selected for use. To conduct the measurement, the face is pressed firmly and squarely into the wet paint immediately after its application. The face is then carefully removed and examined visually. The wet film thickness is the highest scale reading of the notches with paint adhering to it. Measurements should be made in triplicate. Faces of gages should be kept clean by removing the wet paint immediately after each measurement. An alternative circularly notched gage ("hot cake") is rolled perpendicularly through the wet film and the clearance of the deepest face wetted is noted.

 

2.3.9.2 CYLINDRICAL GAGE. A cylindrical wet film thickness gage is described in ASTM D 1212. These gages are also rolled through the paint rather than being pressed into it. They have an eccentric center wheel with constantly changing clearance supported by two outer wheels. The position on the exterior scale corresponding to the point that the wet paint first touches the eccentric wheel indicates the wet film thickness.

 

2.3.10 DRY FILM THICKNESS GAGES FOR COATINGS ON ALUMINUM, COPPER, AND STAINLESS STEEL. Gages are available to determine the dry film thickness of organic coatings on aluminum, copper, and stainless steel. Alternating current from the instrument probe coil induces eddy currents in the metal that in turn induce magnetic fields that modify the electrical characteristics of the coil. ASTM D 1400 fully describes the instrument and its operating procedure.

 

2.3.11 MAGNETIC DRY FILM THICKNESS GAGES FOR COATINGS ON STEEL. There are many different types of gages available for nondestructively determining the film thickness of cured organic coatings on metal surfaces. Most rely on the ferromagnetic properties of steel. Their use is described in detail in ASTM D 1186 and SSPC PA 2. They are available in different thickness ranges to provide the best accuracy with different coating thicknesses. Each has a probe or tip that is placed directly on the coating during measurement.

 

2.3.11.1 MAGNETIC THICKNESS gages should be calibrated before use. It is also a good practice to check the calibration during and after use. Gage suppliers provide a set of standard thickness nonmagnetic (plastic or nonferrous metal) shims to cover their working ranges. The shim for instrument calibration should be selected to match the expected coating thickness. It is placed on a bare steel surface and the gage probe placed on it for calibration. If the instrument scale does not agree with the shim, it should be properly adjusted. If adjustment is difficult, the reading for bare steel can be added or subtracted from field readings to determine actual thicknesses.

 

2.3.11.1.1 THE STEEL SURFACE USED FOR CALIBRATION should be a masked-off area of the steel being painted or an unpainted reference panel of similar steel, if possible. Pull-off gages are best calibrated using small chrome-plated steel panels of precise thickness (Standard Reference Material No. 1358, Certified Coating Thickness Calibration Standard) available from the National Institute of Standards and Technology (formerly the National Bureau of Standards), Gaithersburg, MD 20899. These panels should not be used on magnetic flux gages, because the mass of steel is insufficient for their proper operation. Shims from pull-off gages should not be interchanged with those from magnetic flux gages.

 

2.3.11.1.2 ABOUT FIVE FIELD MEASUREMENTS should be made for every 100 square feet of painted surface. Each of these five measurements should be an average of three separate gage readings taken within an inch or two of each other. Measurements should be made at least 1 inch away from edges and corners.

 

2.3.11.1.3 PULL-OFF GAGES. Pull-off gages measure film thickness by stretching a calibrated spring to determine the force required to pull an attached permanent magnet from a coated steel surface. The simplest type of pull-off instrument is the pencil gage with a coil spring attached to the magnet. It is held in a vertical position on the coated steel and lifted away slowly until the magnet pops off the surface. The paint thickness is indicated by the position of the indicator on the calibrated scale. The attractive force of the magnet varies inversely with the paint thickness. Banana gages (long, narrow instruments) represent another form of pull-off gage. They are more versatile and precise than pencil gages. A helical spring is stretched by manually turning a graduated dial, and a pin pops up when the magnet is lifted. At least one company sells an automatic gage with a dial that turns and stops automatically. Cheaper models have a rubber foot contact for the painted surface. More expensive models have a more durable tungsten carbide foot for greater durability and precision. “V” grooves are cut in the probe housing of these gages and the electrically operated flux gages described below to permit more accurate measurement of paint dry film thicknesses on cylindrical surfaces.

 

2.3.11.2 FLUX GAGES. Magnetic flux gages measure changes in the magnetic flux within the probe or the instrument itself. Flux changes vary inversely with distance between the probe and the steel. Mechanically operated instruments of this type have a horseshoe magnet that is placed directly on the coating, and readings are made from the position of a needle on a calibrated scale. Electrically operated magnetic flux instruments have a separate instrument probe that houses the magnet. Thickness measurements are presented in a digital read-out. Some of these gages have a probe attached to the instrument to permit greater accessibility, especially in laboratory work. They may also have attachments for strip recorders for repetitive work or alarms to produce sounds if minimum thicknesses are not met. For the paint inspector, these more sophisticated attachments are normally unnecessary.

 

2.3.12 DESTRUCTIVE (NONMAGNETIC) DRY FILM THICKNESS GAGE. There are several models of Tooke gage described in ASTM D 4138, Measurement of Dry Film Thickness of Protective Coating Systems by Destructive Means that measure paint dry film thickness on any surface by microscopic observations of precision-cut angular grooves in the film. The gage is not recommended with very soft or brittle films which distort or crumble, respectively, when cut. A dark, thick line is first drawn on the painted surface for later reference under the magnifier. A groove is then firmly cut perpendicular across the line with a tungsten carbide cutter tip as it forms a tripod with two support legs. The width of the cut is determined visually using the illuminated magnifier portion of the instrument. Tips with three different cutting angles are available for use with films of thickness up to 50 mils. Visual observations are multiplied by 1, 2, or 10, depending upon the cutting angle of the tip, to determine the actual film thickness. Thicknesses of individual coats of a multi-coat system can be determined, if they are differently colored.

 

2.3.13 HOLIDAY DETECTOR. Instruments for detecting pinholes and other flaws in coatings on metal surfaces are used mostly on waterfront and fuel storage and distribution facilities but should be used on freshly coated critical metal structures. Holiday detectors are available in two types: low and high voltage, as described in NACE RP0188.

 

2.3.13.1 LOW VOLTAGE HOLIDAY DETECTORS. Low voltage (30 to 90 volts) detectors are used on coatings up to 20 mils in thickness. These portable devices have a power source (a battery), an exploring electrode (a dampened cellulose sponge), an alarm, and a lead wire with connections to join the instrument to bare metal on the coated structure. A wetting agent that evaporates upon drying should be used to wet the sponge for coatings greater than 10 mils in thickness. The wetted sponge is slowly moved across the coated surface so that the response time is not exceeded. When a holiday is touched, an electric circuit is completed through the coated metal and connected wire back to the instrument to sound the alarm. Holidays should be marked after detection for repair and subsequent retesting.

 

2.3.13.2 HIGH VOLTAGE HOLIDAY DETECTORS. High voltage (up to 30,000 volts or more) holiday detectors are normally used on coatings greater than 20 mils in thickness. The rule of thumb is to use 100 volts per mil of coating. The exploring electrode may consist of a conductive brush or coil spring. It should be moved at a rate not to exceed the pulse rate of the detector. If a holiday or thin spot in the coating is detected, a spark will jump from the electrode through the air space or a thin area of the coating to the metal. The resultant hole in the coating will locate the holiday or thin spot that requires corrective action.

 

2.3.14 ADHESION TESTER. There are two basic types of testing for determining adhesion of coatings: the tape and the pull-off test. The tape test is mostly used in the field, and the pulloff test, in the laboratory. The tape test is most useful when adhesion is low. Thus, it is often used to determine whether an old coating has adequate adhesion to support another layer of paint, or whether there is compatibility between coating layers. This test cannot distinguish among good adhesion levels. The pull-off test is more time consuming to perform since a “dolly” or fixture must be glued to the surface of the coating. The test measures the tensile force needed to remove the fixture. Pulloff forces up to several thousand pounds per square inch can be measured.

 

2.3.14.1 TAPE ADHESION TEST. In the tape test, ASTM D 3359, an X or a lattice pattern is cut through the coating to the substrate. Special pressure-sensitive tape is applied over the cut and rapidly pulled off at an angle of 180 degrees. The cut area is then examined for extent of deterioration. A kit is available with a knife, chrome-plated steel template and tape for performing the test.

 

2.3.14.2 PULL-OFF ADHESION TEST. In the pull-off test, ASTM D 4541, a metal dolly is bonded to a coated surface at a perpendicular angle with an adhesive, usually a two-component epoxy. After the adhesive has fully cured, a force is gradually and uniformly applied to the dolly until it is detached from the coating (or until the desired pull-off level is reached). One type of pull-off tester has a hand wheel that is turned to apply the force. The hand wheel/ratchet spanner is tightened until the dolly is detached or a prescribed force is applied. Another type applies the pull force pneumatically with compressed gas. Machine application of pull produces more accurate results than manual application. In both cases, care must be taken to make sure the dolly and instrument are both aligned perpendicular to the coated surface. A horizontal surface is preferred.

 

2.3.15 PORTABLE GLOSSMETER. Battery-powered, pocket-size gloss meters can provide accurate measurements in the laboratory or field. ASTM D 523, Specular Gloss, describes a method for measuring gloss in the laboratory which could be adapted for use with a portable device. Measurements can be made on any plane surfaces.

 

2.3.16 HARDNESS TESTER. A series of hardness pencils (drawing leads) are available for determining rigidity or hardness of organic coatings on rigid substrates. The film hardness is that of the hardest lead that does not cause damage, as described in ASTM D 3363, Film Hardness by Pencil Test. The procedure is used to establish degree of cure, adverse effects of solvents from a wet layer upon a dry film, and softening effects caused by environmental exposure.