What is dead plaster or burnt plaster and how it is made?

Dead plaster or burnt plaster is plaster of Paris (POP) that has lost its setting property because it has been heated too much or exposed to moisture for a long time. It becomes useless for construction purposes.

How Dead Plaster is Made:

• Plaster of Paris is made by heating gypsum (CaSO4·2H2O) at about 150°C.
• If POP is heated above 200°C or left in the open air absorbing moisture, it loses water of crystallization permanently.
• This results in a powder that does not set when mixed with water, known as dead or burnt plaster.

Key Points:

• Dead plaster = POP that cannot harden again.
• It is caused by overheating or absorbing moisture.
• Not useful for plastering or casting.