The use of lime dates back to the Greek and Roman periods, when it was widely used, notably as a building mortar or as a decorative coating.
Lime or calcium oxide (Cao) is obtained by the pyrolysis of a limestone, rich in calcium carbonate (Caco3). The most "fine" calcareous stones produce a lime free of hydraulic materials (clay, iron...). This lime will be in trade, under the name "air lime (CL 90). The most "coarse" stones, will make a lime more or less loaded with hydraulic elements, which will become: >hydraulic lime (NHL).
Air lime makes its intake by carbonation (absorption of the CO² contained in the ambient air). This makes it the lime best suited to coatings and paints.
Its very slow grip (between 24 and 48H) makes its use very flexible and particularly suitable for masonry work. Advantage not to be overlooked: CL lime mortar can be stored for a very long time. Simply pour it into a container (large type bin), cover it with a few centimetres of water that prevents any air intake and close the lid to prevent evaporation (to be monitored from time to time to check the water level).
The hydraulic lime is taken first by water and then by air. It is recommended outside (exposed facades, slabs...) and inside for wet rooms (water rooms, slabs, cellars, buried walls...). It is also often used in hemp insulating coatings (which require a lot of water) in order to promote a faster catch. Unlike air lime, its storage after it has been wasted cannot go beyond 24 hours.