Plaster is a building material used for the protective or decorative coating of walls and ceilings and for moulding and casting decorative elements. In English “plaster” usually means a material used for the interiors of buildings, while “render” commonly refers to external applications.
Walls need plastering so that the rough outside external walls are not showing when you come to move into your home. Therefore the walls are plastered, this is a mixture of lime or cement concrete and sand along with the required quantity of water. After this then the walls can be painted or lined with wall paper with whatever the customer decides.