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How to repair concrete

As concrete buildings begin to take on greater historical importance, the challenge for architects is restoring the material sensitively

For firms taking on a restoration contract, concrete repair can cause a major headache. The threat of litigation looms large, buildings are shrouded in plastic at the very mention of spalling, and huge skirts festoon any publicly accessible areas, lest falling debris hit a passer-by. The evidence of testing – sometimes performed without much expertise – is frequently left exposed for far longer than is necessary. The red-stained scars of excavated reinforcement bars all too often stand accusingly as dramatic evidence of a problem, eroding the quality of the environment for building users. All this leads to an ‘anything has to be better than this’ acceptance of poor-quality patching.

The term ‘concrete cancer’ may have lost popular currency in the last 20 years, but the view of concrete decay as terminal is still widely held. This is a rather bizarre attitude: all building materials are, in effect, gradually decaying, and maintenance and repair is never about creating a time-defying product, but about controlling natural entropy.

We appreciate that stone crumbles and wood moldings lose crispness, but concrete that is no longer pristine is often seen as problematic. We need to develop an understanding of concrete’s life cycle and tailor solutions accordingly.

This links to the question of patina: can dirty, patched or scarred concrete ever look beautiful? We accept – and even preserve – evidence of the passage of time on traditional stone buildings, but there still lingers a belief that concrete which has got a bit grubby needs a vigorous scrub or a coat of paint. There are frequently valid technical reasons for applying coatings to concrete, but these always alter its appearance. Much as a glass extension is never invisible, there is no such thing as a truly transparent protective barrier.

A walk round the wonderfully aged exterior of London’s Barbican Centre should convert even the most determined adherent of the ‘make it look like it was built yesterday’ strategy think twice. The streaking on the balcony fronts add an extra dimension of scale and tone, emphasising the monumentality of the form and the richness of the surface texture. A recent photography competition held by the Twentieth Century Society via the Flickr photo-sharing website generated many entrants, celebrating concrete that was far from crisp and newly formed. The café at the Hayward Gallery in London, which opened under the name Concrete in November 2007, markets itself with cards showing a close-up of a concrete surface – complete with a stain.

Part of the current problem with concrete repair is that we still have a tendency to place blind faith in contractors, or in the manufacturers and suppliers of patented products. Unsurprisingly, many clients are unwilling to support innovation when told that any deviation from factory-batched mixes or standard methods will result in an end product not eligible for guarantee cover. But has anyone ever made a successful claim? I have yet to come across a case.

In fact, much work has been done to improve repair methods, provide sound and accessible advice and share best practice, and many architects (not necessarily those specialising in conservation) have been working intelligently from first principles to come up with innovative solutions.

I am currently working on a guide to concrete repair to be published by English Heritage. This is part of a wholesale revision of its highly respected series of Practical Building Conservation technical handbooks. It’s a sign of the times – back in 1988, when the first series came out, there was no volume on concrete. Now, with so many listed buildings made from concrete, and English Heritage’s skilled masons turning their hands to concrete patchwork,
it has become a necessity.

Armed with a better understanding of decay processes and the confidence to look beyond the standard proprietary solutions, concrete repair in the future should become a fascinating art requiring skill and sensitivity where the quality of the building deserves it.

 

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