What is gypsum plaster ?

Gypsum is a hydraulic binder based on calcium sulfate. This powder material, mixed with water, will produce a slurry, which can be given virtually any form. A crystallization reaction between plaster and water will take place and the slurry will progressively harden and form a crystalline structure, with only a small change in dimension. Finally, a solid is obtained called set gypsum. The setting reaction was investigated from a scientific point of view by Lavoisier in 1768 but this setting reaction had been used for many years before, on a large scale, in building industry and artistic moldings. Ancient Egyptians already used plaster as a jointing material for pyramids and as a chemically inert surface for painting.From a chemical point of view, plaster is made of calcium sulfate hemihydrate CaSO4 0.5H20. Hemihydrate (HH) does not occur naturally but can be obtained from a natural product widely distributed, called calcium sulfate dihydrate (DH) or gypsum rock CaSO4 2H2O (DH). It is ...  more