Sheet rock panels, typically 4-by-8 feet, are nailed or screwed directly into wall-framing studs. Panels are joined in the centers of the framing studs for support. The line, where two panels meet, is called the seam. Sheetrock must be trimmed for detail installation around windows, doors, light fixtures and electrical outlets.
Careful installation, even by a master builder, can result in imperfections on a Sheetrock wall. Sheetrock is essentially compressed mineral powder between two sheets of thin paper. It is a soft material that dents easily. Nails and screws, used for installation, leave dimples in the Sheetrock. Seams, even when perfectly aligned, are visible.
For a professional-looking finish, carpenters and drywall installers smooth the wall to prepare for painting. Smoothing the wall involves applying drywall tape over the seams and filling any depressions made by nails or screws with drywall joint compound. Joint compound is also thinly applied over the tape so their edges are not visible on the painted wall. After the seams are smoothed and the dimples are filled, a thin skim-coat of joint compound is applied over the entire wall to create uniform texture.
Paint comes in a variety of finishes, including flat, eggshell, satin, semi-gloss and gloss. Each finish type has its advantages and disadvantages for particular applications. Less reflective flat and eggshell finishes better conceal imperfections in the wall but are more difficult to clean. Highly reflective semi-gloss and gloss finishes are relatively easy to clean but make flaws more visible.