Plaster of Paris Hardens by

Answer: Plaster of Paris, commonly known as calcium sulphate hemihydrate, is a calcium metal salt.

Plaster of Paris has the chemical formula CaSO4.12H2O. It is made by the extreme heating of gypsum, which is likewise a calcium salt.

When water is added to plaster of Paris, it softens and turns into a paste. The creation of string hydrogen bonding between the molecules of plaster of Paris and water causes this paste to harden over time.