Lime mortar is one of the world’s oldest and most durable building materials; it’s also one of the great survivors. Just look at the Great Wall of China where many sections were built around 518 – 618AD – by ramming earth, lime, sand and small stones between board frames, and lime has been used continuously ever since in the re-building and refurbishment for over 2000 years. It has certainly stood the test of time.
Lime plaster is a traditional building material which, in basic terms, is made by burning limestone, then slaking it with water to form a plaster that hardens with age. It has been used for thousands of years, and when fully cured is extremely durable and hard-wearing. In fact there is evidence of lime being used for ancient Egyptian monuments, and the Romans used it regularly.
New lime plaster is highly caustic and usually requires specialist application, but when successfully applied it provides a highly breathable, flexible but very durable substrate. Its high level of breathability makes it ideal for renovation or restoration projects of older buildings where it would have been used traditionally.
Unlike modern gypsum plaster, lime plaster not only has to dry but also cure, so any ‘coverings’ for lime plastered surfaces should be carefully considered. If you are applying new lime your supplier or specialist plasterer should be able to advise on curing times, but as a general ‘rule of thumb’ we suggest that for every 5mm thickness of lime it needs a minimum of 4 weeks to cure (sometimes longer). This means that no further coatings, whether that’s lime wash, paint, or any other product, should be applied until it has had sufficient curing time.
We recommend Earthborn Paints for lime plastered walls.
Hydraulic lime sets by hydrolysis whereas non-hydraulic lime sets by carbonation.
The hydraulic lime can set underwater, that’s because hydrolysis is a reaction caused by water. The non-hydraulic lime needs air to carbonate and thus set. In physical terms, the two materials are very different to work with.