Lath and plaster
Lath and plaster is a building process used to finish mainly interior walls and ceilings in Canada and the United States until the late 1950s. After the 1950s, drywall began to replace the lath and plaster process in the United States.
In the United Kingdom and its colonies, lath and plaster was often used for interior partition walls and the construction of ceilings, before the introduction of plasterboard in the 1930s. In the U.K., riven or split hardwood laths were often used of random lengths and sizes. Splitting the timber, as opposed to sawing in straight lines, followed the grain of the timber which greatly improved strength and durability. Also, reed mat was used as a lath. The technique derives historically from the earlier, more primitive, wattle and daub.
The wall or ceiling finishing process begins with wood laths. These are narrow strips of wood or split boards, nailed horizontally across the wall studs or ceiling joists. Each wall frame is covered in lath, tacked at the studs. The lath is typically about one inch (2.5 cm) wide by four feet (1.22 meters) long by 1⁄4 inch (6.4 mm) thick. Each horizontal course of lath is spaced about 3⁄8 inch (9.5 mm) away from its neighboring courses.
Temporary lath guides are then placed vertically to the wall, usually at the studs. Plaster is then applied, typically using a wooden board as the application tool. The applier drags the board upward over the wall, forcing the plaster into the gaps between the lath and leaving a layer on the front the depth of the temporary guides, typically about 1⁄4 inch (6.4 mm). A helper feeds new plaster onto the board, as the plaster is applied in quantity. When the wall is fully covered, the vertical lath "guides" are removed, and their "slots" are filled in, leaving a fairly uniform undercoat.
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