C is for Concrete: A-Z of Historic Buildings

Concrete is ancient! Concrete was used by the Ancient Romans during the Imperial period, most notably in the Pantheon. The Pantheon has a domical roof which has a round hole in the top, called an ‘oculus’ (an ‘eye’). This special shape of roof would be completely impossible were it not for concrete, because a masonry dome would need a capstone (otherwise it would collapse). The Romans called their work in this wonder material opus caementicium. The second word should be familiar, since it’s where we get ‘cement’ from. 

This material was, however, a lost art for many centuries until its revival in the 19th century, though there were some early pioneering structures using forms of concrete in the 17th and 18th centuries.

Of course, in the 20th century concrete came into its own as the material of choice of ‘brutalism’, a term brought into English by Rayner Banham in his 1955 essay ‘The New Brutalism’. The material had great expressive possibilities, and remarkable engineering properties.

‘Boardmarked’ concrete showing the impression of wooden planks used to make the formers of poured concrete. This is the iconic National Theatre in the South Bank, London, by Denys Lasdun, a Grade II* listed building. Photography by Tom Parnell, Wikimedia Commons.

Concrete of the modern era presents special problems in historic buildings conservation, and new research is continually hinting at new methods for preserving the material. The Society for the Protection of Ancient Buildings recently completed a research project at a visionary concrete spectators’ stand in Galashiels, Scotland. Reinforced concrete has particular problems owing to corrosion of metal within the concrete, which can be hidden by the solid substance.
Modern concrete finds its way into historic buildings, where it was often used in the 20th century to replace traditional floors. With ‘workaday’ vernacular buildings, the floor was usually just compacted earth, and this has often been replaced with solid concrete slabs. Concrete is far from ideal in this context, since its tight crystalline structure makes it vapour impermeable, potentially pushing water into the walls instead. Further guidance on flooring solutions in traditional buildings can be found in Historic England’s documentation.