Plastering,

Plastering, the art of covering the internal faces of walls, the partitions, and the ceilings of a house or other building with plaster. It is difficult to get plaster to keep completely dry on the inside faces of external walls unless they are first covered with lathing (narrow strips of wood, see LATH). Ceilings and wooden partitions are always lathed so as to hold or key the plaster. Plastering is sometimes done in two, but most usually in three coats. The first or foundation coat is formed of lime and sand (mortar) mixed with hair. This is called pricking if done upon lath, and rendering if it is spread on a bare brick or stone wall. It is crossed with deep incised lines to key the second coat, which consists of fine lime mixed with some coarse plaster of Paris (see GYPSUM) floated on. The first coat should be completely dry before the second is added, but the latter is generally still a little damp when the third coat or set is put on. This last coat is usually composed of a mixture of fine lime, plaster of Paris, and a little size, and is worked so as to produce a very smooth surface. The implements used by the plasterer are chiefly trowels and floating tools, with running moulds for mouldings. Ceiling ornaments and other enrichments are formed of plaster of Paris cast in moulds. Mouldings are run in the same material.