Plaster of Paris is obtained by pulverizing the gypsum (calcium sulphate hemihydrate CaSO4 0.5H2O) which is heated to a temperature of 150 degrees centigrade. When Gypsum (CA SO4,2H2O) is ground to a powder and heated at 150deg to 165deg C, three- quarters of its combined water is removed producing hemi-hydrate plaster (CA SO4,1/2H2O), commonly known as the 'Plaster of Paris 'Upon addition of water, Plaster of Paris (POP) becomes regular gypsum (dehydrate) again causing the resultant material to harden. This hardening material can be used to create moulds for casting and in construction. When this powder is mixed with water the resulting paste sets hard as the water recombines to produce Gypsum again. This process can be repeated almost indefinitely, with important implications for recycling. When dry POP powder is mixed with water it hardens. This material which can be applied over brick, block or concrete surface to form a smooth surface is called gypsum plaster.