Plasterers work on building interiors and exteriors. They apply plaster directly to masonry, wire, wood, metal, or lath. (Lath is a supportive reinforcement made of wood or metal that is attached to studs to form walls and ceilings.) These surfaces are designed to hold the plaster in position until it dries. After checking the specifications and plans made by the builder, architect, or foreman, plasterers put a border of plaster of the desired thickness on the top and bottom of the wall.
After this border has hardened sufficiently, plasterers fill in the remaining portion of the wall with two coats of plaster. The surface of the wall area is then leveled and smoothed with a straightedge tool and darby (a long flat tool used for smoothing).
Plasterers then apply the third or finishing coat of plaster, which is the last operation before painting or paperhanging. This coat may be finished to an almost velvet smoothness or into one of a variety of decorative textures used in place of papering.
When plastering cinder block and concrete, plasterers first apply what is known as a brown coat of gypsum plaster as a base. The second coat, called the white coat, is lime-based plaster. When plastering metal lath foundations, they first apply a scratch coat with a trowel, spread it over the lath, and scratch the surface with a rake-like tool to make ridges before it dries so that the next coat-the brown coat-will bond tightly. Next, the plasterer sprays or trowels the plaster for the brown coat and smoothes it. The finishing coat is either sprayed on or applied with a hawk and trowel. Plasterers also use brushes and water for the finishing coat. The final coat is a mix of lime, water, and plaster of paris that sets quickly and is smooth and durable.
The plasterer sometimes works with plasterboard or sheetrock, which are types of wallboard that come ready for installation. When working with such wallboard, the plasterer cuts and fits the wall-board to the studding and joists of ceilings and interior walls. When installing ceilings, workers perform as a team.
Plasterers who specialize in exterior plastering are known as stucco masons. They apply a weather-resistant decorative covering of Portland cement plaster to lath in the same manner as interior plastering or with the use of a spray gun. In exterior work, however, the finish coat usually consists of a mixture of white cement and sand or a patented finish material that may be applied in a variety of colors and textures.
Decorative and ornamental plastering is the specialty of highly skilled molding plasterers. This work includes molding or forming and installing ornamental plaster panels and trim. Some molding plasterers also cast intricate cornices and recesses used for indirect lighting. Such work is rarely used today because of the great degree of skill involved and the high cost.
In recent years, most plasterers began using machines to spray plaster on walls, ceilings, and structural sections of buildings. Machines that mix plaster have been in general use for many years.