LIME MORTAR – LIME RENDER – LIME PLASTER – LIMEWASH – LIMECRETE
Lime is used instead of cement in mortar, render and plaster. It is also used to make limewash, and an alternative to concrete called limecrete.
Lime is undergoing a revival as a natural building material after falling out of favour in the 20th Century. Virtually all traditional buildings in the UK used lime as a mortar, render, plaster or wash before cement and gypsum became more widespread in the mid 19th Century.
Building materials based on lime are “soft but tough”. They work in harmony with seasonal and long-term changes in the building, accomodating tiny movements without cracking and allowing moisture to evaporate away harmlessly. Lime, like cement, is burnt in a kiln, but the process requires 80% less energy.
Lime is used in natural building because its carbon footprint is much lower than that of cement, but lime also has the advantage of providing breathability. Lime’s breathability is an advantage in that it creates a humidity-regulated, healthy environment. Lime-based materials absorb moisture when humidity is high and release moisture when humidity is low, avoiding problems of dampness and condensation and creating a pleasant atmosphere.
Many old buildings in the UK are suffering because of the effects of cement. Cob, clay lump, stone, timber frame and wattle and daub buildings that would have originally been rendered and plastered with lime have had cement applied to them in the 20th Century. The cement traps moisture inside the wall, reducing the strength of earth based materials (sometimes to the point of failure) and causing timber to rot and stone to crack. Buildings like these should have the cement removed and it should be replaced to lime – if not then buildings that have lasted for centuries will not last much longer.
Limecrete is a low-carbon, flexible alternative to concrete. Like concrete, it uses a mixture of sand and stones, but hydraulic lime instead of cement is added. Carbon emissions will be much lower, but limecrete also brings the other advantages of lime to the concrete application. Limecrete is more flexible than concrete, so will continue to function where concrete cracks and it also breathable. This makes limecrete ideal for floors in old houses. Concrete floors applied in the last century force moisture sideways and into the walls, whereas limecrete floors work in harmony with the old building, absorbing and releasing to moisture to maintain fairly constant levels.
Limecrete can also be used instead of concrete in foundations. It’s become common practice in sustainable building to make foundations based on a compacted rubble trench capped with a limecrete strip. This “self-draining” foundation discourages damp and also dramatically reduces the amount of lime or cement required as much of the foundation volume is just rubble. This is gaining popularity as a modern technique, but also has a strong historical precedent: the Houses of Parliament are built on self-draining limecrete foundations.