Gyproc One Coat Plaster is a brand name of Gypsum Range of Products manufactured by Saint Gobain India Pvt. Ltd. It is manufactured by heating the prepared raw gypsum. Heating the raw gypsum forces a chemical reaction in the gypsum to change it from dihydrate, CaSO4. 2H2O, to hemihydrate, CaSO4.½H2O, by driving off 1½ of the molecules of water, known as the 'water of crystallization'.