In its raw state, limestone is a sedimentary rock composed primarily of calcium carbonate. It most commonly forms in warm shallow marine waters from the deposition of shells and the bodies of tiny marine organisms. While most limestone around the world has biological origins, it can occasionally be created through other chemical processes. One example is in some humid caves where mineral rich water seeps through the earth and covers the interior surfaces. As the water evaporates, it leaves behind a layer of limestone, sometimes in the form of stalactites and stalagmites. Limestone is categorized by its process of formation as well as its total chemical makeup. The proportions of clay, magnesium, and other trace minerals can greatly affect the specific qualities of the lime in construction.
Lime has been used for making durable mortars and plasters for thousands of years. Burning raw limestone at high temperatures (825 °C or 1,517 °F) transforms the mineral into calcium oxide or “quick lime.” Quick lime is then slaked in water to produce calcium hydroxide, known as lime putty or builder’s lime. When this process takes place naturally inside the earth, we call the product Naturally Hydraulic Lime (NHL.) There are vast deposits of NHL on the Asian and European continents.
The qualities of lime plasters vary according to the source of the lime, the kinds of aggregates and other ingredients added, the application method, and other factors. When we specify lime plaster for a particular project, we select our mix based on a matrix of desired properties including color, texture, strength/weight ratio, density, and hardness. Rather than just buying a product off the shelf, we are committed to helping take lime plastering back to its artisanal roots. Through our work with communities around the world, we help keep this craft relevant, advising entrepreneurs, manufacturers and government agencies on production and regulation standards.