Over the years, many buildings have been stripped of their render in the mistaken belief that exposed masonry is historically authentic. Yet in the past, most buildings were covered with a protective coat of plaster to deter the damaging effects of wind, rain and frost. 'What's now regarded as complicated was a simple, elementary building practice that could be done by all. It required some attention to detail and a good understanding of how buildings performed and looked,' says builder Tim Meek, a Yorkshireman who has been working with lime since the 1980s. He remembers being on a field trip to Prudoe Castle, where he noticed that those undertaking conservation work were 'working in a very different way to what had been done there in the past. I started looking very closely at the materials and the craftsmanship of lime and noticed how careful the work was. All I've done is copy it. Very few others were doing this at the time'. Now based in Scotland, Mr Meek has worked all over Britain and as far afield as America and the Caribbean.

Unlike Portland cement, which became popular from the 1830s because of its fast drying time and effectiveness under water, lime mortar doesn't become stiff and brittle; it allows some movement, and is permeable, enabling buildings to breathe. It is also very Green, not only in the way it is produced, but also because it reabsorbs CO2 from the atmosphere. 'It therefore sits nicely in both the worlds of building conservation and environmentally friendly new architecture.' He adds that 'aesthetically, there is simply no substitute'.

He makes his own lime putty, adding water to calcium oxide (quick lime) and leaving it to slake for months to produce calcium hydroxide (lime putty). He then mixes in sand and sometimes hair for extra strength to produce a mortar which can be used to bed stones or bricks, or for plastering walls. For roughcast renders, coarser aggregates (grit or shells) are added, which increase the surface area, thereby maximising water evaporation. This is the norm in wet areas, such as Scotland, where it is known as 'harling' because the plaster is thrown or 'hurled' onto the surface rather than trowelled.

'Lime plaster should be used sparingly and economically,' says Mr Meek. First, the wall surface and joints are 'packed out' with small pieces of tile, stone and brick embedded in mortar and left for about a week. Then, one or two coats of render are applied. Regular spraying with water is an important part of the process, as is keeping the wall covered with a tarpaulin.

For internal walls and ceilings, the technique is broadly similar, although drying may take longer, and a third, more refined coat may be applied. With modern plasterboard partitions, which lack texture and natural irregularities, it is possible to create the appearance of lime plasterwork (although it will not be permeable) by mixing lime and sand with polyvinyl acetate, skimming it on, and, once it has firmed up, running in a coat of fine, sandy limewash, and then limewashing on top.

Limewash is a liquid mix of lime putty, water and pigments which, applied liberally in three or four coats, provides a protective, permeable and beautifully coloured finish. It is cheap and easy to apply, and, being alkaline, has good sterilising properties. Mixed with earth pigments, it produces a range of gorgeous earth colours that weather beautifully and have a luminosity and patina unrivalled by paint.

Tim Meek 01381 610446

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Traditionally, most buildings were protected by a lime render and limewash< /em>

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