Plasteringone of the oldest crafts in the building tradesremains popular due to the relatively low cost of the material and overall durability of work. Plasterers apply plaster to interior walls and ceilings to form fire-resistant and relatively soundproof surfaces. They also apply plaster veneer over drywall to create smooth or textured abrasion-resistant finishes. In addition, plasterers install prefabricated exterior insulation systems over existing wallsfor good insulation and interesting architectural effectsand cast ornamental designs in plaster. Stucco masons apply durable plasters, such as polymer-based acrylic finishes and stucco, to exterior surfaces. Plasterers and stucco masons should not be confused with drywall installers, ceiling tile installers, and tapersdiscussed elsewhere in the Handbookwho use drywall instead of plaster when erecting interior walls and ceilings.
Plasterers can plaster either solid surfaces, such as concrete block, or supportive wire mesh called lath. When plasterers work with interior surfaces, such as concrete block and concrete, they first apply a brown coat of gypsum plaster that provides a base, which is followed by a second, or finish, coatalso called “white coat”made of a lime-based plaster. When plastering metal lath foundations, they apply a preparatory, or “scratch,” coat with a trowel. They spread this rich plaster mixture into and over the metal lath. Before the plaster sets, plasterers scratch its surface with a rake-like tool to produce ridges, so that the subsequent brown coat will bond tightly.
Helpers prepare a thick, smooth plaster for the brown coat. Plasterers spray or trowel this mixture onto the surface, then finish by smoothing it to an even, level surface.
For the finish coat, plasterers prepare a mixture of lime, plaster of paris, and water. They quickly apply this to the brown coat using a “hawk”a light, metal plate with a handletrowel, brush, and water. This mixture, which sets very quickly, produces a very smooth, durable finish.
Plasterers also work with a plaster material that can be finished in a single coat. This “thin-coat” or gypsum veneer plaster is made of lime and plaster of paris and is mixed with water at the jobsite This plaster provides a smooth, durable, abrasion-resistant finish on interior masonry surfaces, special gypsum baseboard, or drywall prepared with a bonding agent.
Plasterers create decorative interior surfaces as well. One way that they do this is by pressing a brush or trowel firmly against a wet plaster surface and using a circular hand motion to create decorative swirls.
For exterior work, stucco masons usually apply stuccoa mixture of Portland cement, lime, and sandover cement, concrete, masonry, or lath. Stucco may also be applied directly to a wire lath with a scratch coat, followed by a brown coat and then a finish coat. Stucco masons may also embed marble or gravel chips into the finish coat to achieve a pebblelike, decorative finish.
When required, plasterers apply insulation to the exteriors of new and old buildings. They cover the outer wall with rigid foam insulation board and reinforcing mesh, and then trowel on a polymer-based or polymer-modified base coat. They may apply an additional coat of this material with a decorative finish.
Plasterers sometimes do complex decorative and ornamental work that requires special skill and creativity. For example, they may mold intricate wall and ceiling designs. Following an architect’s blueprint, plasterers pour or spray a special plaster into a mold and allow it to set. Workers then remove the molded plaster and put it in place, according to the plan.