Plaster of Paris should be stored in a moisture-proof container. Explain why ?

Explanation

This is because in presence of moisture, plaster of Paris sets to give a hard mass.
`underset("Plaster of Paris")(CaSO_4 . 1//2 H_2O ) + 3//2 H_2O to underset("(Hard mass)")(CaSO_4. 2H_2O)`