Lime is a binder made from limestone cooked at a very high temperature of about 900°C (calcination). After treatment it is available in the form of a clear powder packaged in bags. There are three types of lime. Non hydraulic lime, whether calcic (CL) or dolomitic (DL), can only harden when exposed to air. Natural hydraulic lime (NHL), less pure in limestone than the former, hardens first when exposed to water and then air. The third category of lime, called artificial hydraulic lime (AHL), is actually a type of thinned cement.