Plaster

From Encyc

Plaster is a substance made of a mixture of ground lime, sand and water. When freshly made, it is a paste. It dries to a make a fairly hard substance.

In building, it is applied to internal walls and sometimes ceilings. It dries to a smooth surface, covering over the irregularities of bricks and breeze blocks. This surface may then be covered with paint or wallpaper.