PLASTERING is the art of covering the surface of a wall or ceiling with lime or plaster in order to give it a smooth and uniform sur face, and generally in interiors to fit it for painting or decoration. Technically the term plastering is used only when the plaster is spread over a screen of laths fixed to the wall. In modern usage this lath may be of perforated sheet metal, or a heavy paper board, called plaster board, maybe substituted for the wooden laths. The chief preparations used by plaster ers are known as coarse stuff, fine stuff, plasterer's putty, and gauged stuff. The first of these is composed of sand and lime, mixed with long ox hair; the second is slaked lime, usually without hair; the third is not unlike the second; and gauged stuff is a mixture of plasterers' putty and plaster of Paris. Three kinds of plastering are distinguished, namely, one-coat (lath and lay), two-coat (lath, lay and set), and three-coat (lath, lay, float and set). In one-coat work a layer of coarse stuff is spread over the laths and pressed well into the spaces so as 'to form a key to hold the coat in place. When a second coat is to be applied, the first is not smoothed, but roughened with a birch-broom so as to retain the second one in place. The second coat consists of fine stuff, putty or gauged stuff. In plastering the in terior of houses a first coat is laid on of coarse stuff, the process being known as prick ing-up. The face of the first coat, which
should be of considerable thickness, is troweled or indented diagonally with the point of a lath to form a key for the finishing coats. The second coat is applied to this when it is thor oughly dried. It consists of fine stuff, and is rubbed in with a flat board so as thoroughly to fill the indentations and cover the unequal sur face of the first coat with a smooth and even one. In plastering walls great care must be taken to have the surface perfectly vertical. This second coat is called the floated coat, be cause wooden boards, known as floats, are used in rendering the surface plane. Before drying this coat is scraped with a birch-broom to form i a key for the next. The setting coat is ap plied to the second after it has become per fectly dry. If the wall is to be papered this coat is of fine stuff. (See BUILDING; GYPSUM; LATHS). Consult Eckel, E. C., 'Cements, Limes and Plasters' (New York 1905) ; Hodg son, F. T., 'Mortars, Plasters, Stuccos, Arti ficial Marbles, Concretes, Portland Cements and Compositions' (Chicago 1914); Millar, 'Plas tering) '(London 1892) Richey, H. G., 'Build ing Mechanics' Ready Reference: Cement Workers' and Plasterers' Edition' (New York 1908).