Definition - What does Plaster mean?
A plaster is a calcium sulfate dihydrate material used to cement a structure into a state of rigidity, or adhere some material to another surface. It is applied in a paste form by mixing with water prior to application. Plasters are applied to serve as a thick protective coating on walls and metal surfaces.
Corrosionpedia explains Plaster
Certain metals such as copper do not corrode when housed in a plaster confinement. This is true even in the most severe corrosion-inducing conditions with alternating electrochemical ion levels and wet/dry conditions.
Before plaster is used as a corrosion prevention tool, the chemical composition of the metals should be examined to ensure their suitability with plaster.