What is Plaster of Paris?
Plaster of Paris, or simply plaster, is a type of building material based on calcium sulphate hemi-hydrate (gypsum), nominally CaSO4 ½ H2O). It is created by heating gypsum to about 150º C. Heating also takes place when re-mixed with water (casting), hardening to a smooth solid which does not shrink or lose volume, because it hardens before all the water can evaporate. It is a common building material as well as a versatile medium in sculpture.
