How to plaster speaks plaster techniques, why plaster and what is plaster to the various techniques that can be used.
Plaster can be applied by either by machine or by hand. Machine application is essentially a spraying process. Hand application is done with two very simple tools, a hawk in one hand to hold a small quantity of plaster ready for use and a trowel in the other hand to lift the plaster from the hawk, apply it to the surface and smooth it into place.
Plaster is transferred from the hawk to the trowel with a quick practiced motion of both hands and the trowel is moved up the wall or across the ceiling to spread the plaster, much as one uses a table knife to spread soft butter. After a surface is covered with plaster, it is levelled by drawing a straightedge called a darby across it, after which the trowel is used again to smooth the surface.
Until a few decades ago, the most common form of lath consisted of thin strips of wood nailed to wood framing with small spaces left between the strips to allow keying of the plaster. Most lath today is made of either expanded metal or preformed gypsum boards. The skilled tradesperson who applies lathe and trim accessories is known as a lather.
Expanded metal lath is made from thin sheets of metal that are slit and stretched in such a way as to produce a mesh of diamond shaped openings. It is applied to light gauge steel studs with self drilling, self tapping screws or to wood studs with large headed lathing nails. Lath used with Portland cement stucco is galvanized to deter corrosion.
Gypsum lath is made in gypsum board sheets 16 X 48 inches (406 X 1220 mm) and 3/8 inch (9.5 mm) thick. It consists of sheets of hardened gypsum plaster faced with outer layers of a special absorbent paper to which fresh plaster readily adheres and inner layers of water resistant paper to protect the gypsum core.
Gypsum lath is attached to steel or wood studs with screws. Gypsum lathe cannot be used as a base for gauged gypsum lime finish plasters or Portland cement stucco, as these materials will not bond adequately to the paper facing.
Veneer plaster base (gypsum veneer base) is a paper faced gypsum board that comes in sheets 4 feet (1220 mm) wide, 8 to 14 feet (2440 – 4270 mm) long and ½ or 5/8 inch (13 -16 mm) thick. It is screwed to wood or steel studs, or nailed to wood studs and used as a base specifically for the application of gypsum veneer plaster.