Explain in detail about calcium sulphate hemihydrate i.e. plaster of paris ?

Asked by  | 23rd Mar, 2008, 08:52: AM

Expert Answer:

Plaster of Paris, or simply plaster, is a type of building material based on calcium sulfate hemihydrate, nominally CaSO4·0.5H2O. It is created by heating gypsum to about 150 °C.

2 CaSO4·4H2O → 2 CaSO4·H2O + 3 H2O When the dry plaster powder is mixed with water, it re-forms into gypsum. Plaster is used as a building material similar to mortar or cement. Like those materials plaster starts as a dry powder that is mixed with water to form a paste which liberates heat and then hardens. Unlike mortar and cement, plaster remains quite soft after drying, and can be easily manipulated with metal tools or even sandpaper. These characteristics make plaster suitable for a finishing, rather than a load-bearing material.

Answered by  | 7th Jun, 2008, 08:04: AM

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