I t’s all very well architects arguing over the finer points of philosophy, but brutalism is as much about the nitty-gritty of gravel and cement as it is about artistic expression. It was down to engineers and builders to interpret these highfalutin ideas and bring them into reality. Sometimes they would influence the architects so strongly, with all the new possibilities of construction available, that they would in turn act as both muse and creators in this relentless rush of innovation.

Initially the modernists’ use of reinforced concrete was half-hearted compared to the swaggering feats of engineering going on at the same time. Ove Arup, the great 20th-century engineer, wrote in 1926 that ‘the best architecture in reinforced concrete is generally that to be found among those big engineering structures’ – by which he meant bridges, silos, hydraulic dams and the like. But it wasn’t so great for creating places you could live in. Problems such as heat loss and noise penetration meant that this interwar concrete was a flawed material, used as it was very thinly for walls. But such was the speed at which the science of concrete engineering moved that within 15 years these issues had been largely addressed, if not entirely solved. Water penetration and staining remained hard problems to beat, and the addition of asbestos cement as insulation in some schemes has not left a happy legacy. Still, without constant advances in chemical science and construction techniques much of modern architecture would never have been possible.

Ove Arup was a trusted lieutenant to the new architecture establishment. He was just one of a great number of structural engineers who made the abstract dreams of modern architects a concrete reality (often literally). There was Owen Williams, who as well as being one of the foremost engineers of interwar modernism, worked on many of the great road schemes in Britain such as the Gravelly Hill interchange near Birmingham, better known as that dizzying landmark, Spaghetti Junction. The Smithsons relied on the practical nous of Ove Arup employee Ron Jenkins to realize their demanding Smithdon school design. And perhaps most crucially, the epic concrete dreams of Oscar Niemeyer at Brasília could not have come to pass without the extraordinary engineering genius of Joaquim Cardoso, a published poet, short-story writer and editor.

One of the most appealing aspects of brutalism is the coming together of the different skills of architect, engineer and builder to create something genuinely new. Not that everything always worked smoothly. Arup, for one, could be scathing about the designs he was presented with. But ever the problem-solver he would look to ways to improve them and turn them into reality. Writing in the January 1969 edition of Structural Engineer magazine, he described architects as ‘prepared and indeed determined to design their buildings in reinforced concrete – a material that they knew next to nothing about – even if it meant using concrete to do things that could be done better and more cheaply in another material.’ The architects’ demands placed a heavy burden on the engineers, who, in a pre-computer age, had teams of people engaged for months to work out the complex calculations and formulas needed to ensure these new and challenging designs were structurally sound.

There is, of course, nothing innately modern about concrete, this Roman leftover rediscovered by the Victorians. As Adrian Forty writes so beautifully in his book, Concrete and Culture, it is a material that is equal parts chemistry and physics. The engineers deal with the physics, and the construction companies with the chemistry. An average batch of concrete might be made from one part Portland cement, two parts dry sand, three parts dry stone, and half a part of water. To strengthen it, steel reinforcing bars, or rebars, are laid in the formers and cooked into the concrete like a sixpence in a Christmas pudding. This extra ingredient, the reinforcing, was developed in the 19th century. It was followed in 1905 by the concrete mixer, which helped concrete on its way to become a truly mass-produced material.

Whether on site or in a factory, concrete components are created using formwork or shuttering. These are the jelly moulds: wooden boxes that get filled with poured concrete. The secrets of good shuttering are as complicated as those for good concrete. The trickiest hazard can be that the concrete leaks into the wooden formwork and so becomes impossible to separate from the mould once dry. Unlike wood or stone, concrete doesn’t really have its own shape, and so instead takes on the ghost of whatever it’s moulded in. We see these formwork phantoms in the finish of many modernist structures, inside and out. There’s the intimate detail of wooden planks on the walls at the National Theatre in London, where the mix of aggregates (marine-dredged ballast, fine aggregate of Leighton Buzzard sand, two types of waterproof cement) was very carefully monitored to get that exact result. But these striations aren’t always the desired effect. A rougher aggregate, using bigger pebbles, was used for Basil Spence’s short-lived Glasgow landmark; the Queen Elizabeth Square flats, where evidence of the moulds was writ large rather than small. Meanwhile at the Barbican in London, the finish of the formwork was obliterated, as every granite-dust concrete surface was meticulously bush-hammered by hand to give it that distinctive rugged, rocky appearance. Extravagant experiments yielded other, yet more complex, results. Concrete fetishist Paul Rudolph favoured a technique called ‘roping’, which created channels to direct water downwards, leading the weathering to occur in the grooves rather than across all the surfaces.

Queen Elizabeth Square flats, Glasgow, UK.

Architect: Basil Spence.

Of course, not all brutalist buildings are overwhelmingly concrete. Take the sturdy Ham Common flats designed by James Stirling and James Gowan in South West London, at Langham House Close (1957–58). Here, the concrete frame is filled in by reused yellow London stock brick, creating something that is at once locally familiar and startlingly new. The solid two- and three-storey flats run along a slender side road, their squat forms defined by the hefty concrete beams carrying the load of the structure. Greater London Council architect Kate McIntosh would take this approach much further, reacting against the harshness of what she saw as an overreliance on concrete for her masterpiece, Dawson’s Heights (1964–72), in East Dulwich, London. The two main blocks of the estate exaggerate the hilltop on which they are built, creating a red brick and concrete crest, with balconies jutting out to create a fascinating irregular pattern across the surface of these great brutalist ziggurats. Like the Ham Common flats, they are a reminder of the variety of materials embraced by a style that is now remembered only for one.