Plaster of paris should be stored in a moisture-proof container explain why?

Explanation

Plaster of Paris is a white powder and on mixing with water, it changes to gypsum giving hard solid mass.
`underset("Plaster of Paris")(CaSO_(4).(1)/(2) H_(2)O +1(1)/(2) H_(2)O) to underset("Gypsum")(CaSO_(4). 2H_(2)O)`
To prevent this reaction, Plaster of paris should be stored in a moisture-proof container.