There is but one question on the lips of Andrew Shepherd when the conservation architect touches down in airports to work on restoration projects in foreign lands: ‘what’s your local lime like?’ It might seem an unlikely opener, but to those who earn their living in building conservation, Andrew’s question will scarcely raise an eyebrow. In recent years, lime has played a leading role in the conservation of our built heritage. It is no exaggeration to say that without this magic stuff many of the world’s ancient monuments would slowly be turning to dust.

Lime’s role in the conservation of old buildings is relatively new, though. For most of its working life, lime has been a building material, a binder for mortar and plaster. We don’t know exactly when man first started burning limestone to produce quicklime but we do know that it is a very ancient practice: the earliest surviving example of the material was found in an 8000 BC floor in modern-day Turkey. The Cretan civilisation also used the material as a mortar as did the various dynasties that built the Great Wall of China.

Lime continued to be used right up until the middle of the 19th century when cement was first developed. By the beginning of the 20th century, cement, which is quick-setting and easy to work with, had superseded lime and by the 1950s, the demand for volume housing meant it had virtually vanished from the building site.

Crumbling resolve
Then, in the 1970s, around 20 years after the material had fallen from grace, architects had a rude awakening: historic buildings which had been repaired with cement half a century previously were beginning to crumble like biscuits. Constructed from softer and more porous materials than modern buildings, these historic structures had effectively been suffocated by cement which doesn’t allow walls to breathe. By contrast, lime mortar is porous and allows moisture to evaporate, keeping a building dry inside. It is also softer and weaker than cement, which helps older buildings cope with movement because it flexes.

‘A building’s maintenance cycle is around 40 years,’ explains Andrew. ‘The problems incurred by having used cement such as damp, peeling paint, failing plaster and cracking render only became apparent four or five decades after the repairs had been made.’

Degrees of difference
The 1970s also saw the birth of Britain’s first university courses in architectural conservation. The Architectural Association, one of the most prestigious and selective architecture schools in Britain, was the first, in 1975, and has since been joined by 14 others across the country including Bath University’s MSc in the conservation of historic buildings, Oxford Brookes’ MSc in historic conservation delivered in collaboration with Oxford University’s department for continuing education at Rewley House, and Plymouth University’s MA in architectural conservation.

This substantial academic provision reflects the UK’s abiding public interest and concern for the historic environment and our ancient heritage. It is a longstanding concern. This, after all, is the country where the father of architectural conservation, William Morris, founded the Society for the Protection of Ancient Buildings in 1877 – the principles of which remain to this day the philosophical basis of the institution’s work – and which, in turn, gave birth to international charters such as the International Commission on Monuments and Sites (ICOMOS).

Material matters
Unlike first degrees in architecture, these postgraduate building conservation courses recognise that conservation has its own philosophical and political identity for which specialised training and education are needed. The programmes follow the ICOMOS guidelines on education and training which means that in addition to lectures and seminars, students participate in hands-on site visits to give them direct experience of the practical application of conservation principles. In the words of Oxford Brookes course leader, Dr Michelle Thomas: ‘you can’t possibly understand how materials work until you’ve had direct experience of them. So our students go to brickyards and make bricks, they make sash windows and cob walls, and mix lime in a bath tub. If they are going to specify properly one day, they need to understand the vocabulary and process of materials.’

Global preservation
It has been a long time coming, but concern for the historic built environment has also spread to parts of the developing world from where many of the students on Britain’s courses now come – as yet, there are virtually no courses outside western Europe. To be frank, tourism is a strong driver behind this new interest in heritage but the result is that in countries such as India, Taiwan and China government money is now available for graduates, mainly architects and engineers, to learn how to conserve and adapt their built heritage to meet the requirements of the 21st century. In addition, when students return home the paucity of conservation practitioners in this fast-growing sector means they are often able to directly influence the evolution of conservation in their countries of origin.

Nowhere more so than in the use of lime, a time-honoured material that is universally available, but about which many developing countries, which see the material as old-fashioned, need to be educated. ‘Lime is good and concrete is bad. When I am on international lecture tours, I make my students repeat it like a mantra,’ says Andrew Shepherd.

Green credentials
Lime isn’t just good because it allows traditional buildings to breathe. Its environmental credits are huge, too. When limestone is burned to produce lime, it gives off carbon dioxide. But later, when it is setting on a building, it re-absorbs the gas. Cement also produces carbon dioxide during production but it never re-absorbs it. In fact, cement production accounts for just over eight per cent of man’s CO2 emissions.

Lime also has economic advantages over cement which, critically for developing countries, often requires expensive imported fuels and equipment, and large centralised plants. Conversely, locally available lime is easily produced on a small scale and, unlike cement production, is generally labour intensive, providing local employment in parts of the developing world where unemployment rates are high. Finally, because it takes longer to set than cement, lime is more forgiving, allowing time for mistakes to be corrected.
 

Writen by Karen Glaser, a freelance journalist who writes for a range of publications including  The Guardian and The Times. She used to edit the architectural interiors magazine Intra  and was also features editor on Building Design, the architectural weekly.

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