They immediately use the trowel to press a paper tape used to reinforce the drywall and to hide imperfections into the wet compound and to smooth away excess material. Nail and screw depressions also are covered with this compound, as are imperfections caused by the installation of air- conditioning vents and other fixtures. On large commercial projects, finishers may use automatic taping tools that apply the joint compound and tape in one step. Finishers apply second and third coats, sanding the treated areas after each coat to make them as smooth as the rest of the wall surface. This results in a very smooth and almost perfect surface.
Some finishers apply textured surfaces to walls and ceilings with trowels, brushes, or spray guns.
Lathers apply metal or gypsum lath to walls, ceilings, or ornamental frameworks to form the support base for plaster coatings. Gypsum lath is similar to a drywall panel, but smaller. Metal lath is used where the plaster application will be exposed to weather or water, or for curved or irregular surfaces for which drywall is not a practical material. Lathers usually nail, screw, staple, or wire-tie the lath directly to the structural framework. Drywall installation can be very strenuous.