<Tr> <Td> </Td> <Td> This section does not cite any sources . Please help improve this section by adding citations to reliable sources . Unsourced material may be challenged and removed . (March 2012) (Learn how and when to remove this template message) </Td> </Tr> <P> 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 ⁄ inch (6.4 mm) thick . Each horizontal course of lath is spaced about ⁄ inch (9.5 mm) away from its neighboring courses . </P> <P> 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 ⁄ 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 . </P> <P> In three coat plastering it is standard to apply a second layer in the same fashion, leaving about a half inch of rough, sandy plaster (called a brown coat or browning (UK)). A smooth, white finish coat goes on last . After the plaster is completely dry, the walls are ready to be painted . In this article's photo ("lath seen from the back ...") the curls of plaster are called keys and are necessary to keep the plaster on the lath . Traditional lime based mortar / plaster often incorporates horsehair which reinforces the plasterwork, thereby helping to prevent the keys from breaking away . </P>

When did they stop using horse hair plaster