They apply durable plasters such as polymer-based acrylic finishes and stucco to exterior surfaces, and may install prefabricated exterior insulation systems over existing walls for good insulation and interesting architectural effects. In addition, they may cast ornamental designs in plaster. Drywall workers and lathers a related occupation use drywall instead of plaster when erecting interior walls and ceilings. They spread this rich plaster mixture into and over the metal lath. Before the plaster sets, they scratch its surface with a rake-like tool to produce ridges so the subsequent brown coat will bond to it tightly.
Laborers 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. 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 on the job site.