Drywall is a common building material typically made of a layer of gypsum plaster pressed between two thick sheets of paper, then kiln dried. Drywall is used globally for the finish construction of interior walls and ceilings.
"In 1990, four major trade associations, the Association of Wall and Ceiling Industries International (AWCI), the Ceilings and Interior Systems Construction Association (CISCA), the Gypsum Association (GA), and the Painting and Decorating Contractors of America (PDCA), presented the consensus document Levels of Gypsum Board Finish. The document was created to "precisely describe" the desired finish of walls and ceilings prior to final decoration. This precise description enables contractors to better understand the requirements of architects and building owners in order to enhance the satisfaction of the client. Specifications that include the Levels of Gypsum Board Finish also promote competitive bidding that allows the bidder to consider the correct labor and materials to finish the wall suitably for its final decoration." [1]
The official document (summarized below) is known as GA-214-96 "Recommended Levels of Gypsum Board Finish".
Level 0
No taping, finishing, or accessories required.
Usage: Temporary construction or when final decoration is undetermined.
Level 1
All joints and interior angles shall have tape set in joint compound. Surface shall be free of excess joint compound. Tool marks and ridges are acceptable.
Usage: Above false ceilings or other areas which are out of public view where a degree of fire and noise resistance is required.
Level 2
All joints and interior angles shall have tape embedded in joint compound and wiped with a joint knife leaving a thin coating of joint compound over all joints and interior angles. Fastener heads and accessories shall be covered with a coat of joint compound. Surface shall be free of excess joint compound. Tool marks and ridges are acceptable. Joint compound applied over the body of the tape at the time of tape embedment shall be considered a separate coat of joint compound and shall satisfy the conditions of this level.
Usage: As a substrate for tile walls and ceilings as well as in garages, warehouses, and other places where appearance is not a primary concern.
Level 3
All joints and interior angles shall have tape embedded in joint compound and one additional coat of joint compound applied over all joints and interior angles. Fastener heads and accessories shall be covered with two separate coats of joint compound. All joint compound shall be smooth and free of tool marks and ridges. It is recommended that the prepared surface be coated with a drywall primer prior to the application of final finishes.
Usage: Suitable base for heavy-medium textured paint or other thick finishes.
Level 4
All joints and interior angles shall have tape embedded in joint compound and two separate coats of joint compound applied over all flat joints and one separate coat of joint compound applied over interior angles. Fastener heads and accessories shall be covered with three separate coats of joint compound. All joint compound shall be smooth and free of tool marks and ridges. It is recommended that the prepared surface be coated with a drywall primer prior to the application of final finishes.
Usage: "Standard" household and office walls. Used with light or non-textured finishes. Not suitable for harsh lighting conditions which may highlight minor imperfections.
Level 5
All joints and interior angles shall have tape embedded in joint compound and two separate coats of joint compound applied over all flat joints and one separate coat of joint compound applied over interior angles. Fastener heads and accessories shall be covered with three separate coats of joint compound. A thin skim coat of joint compound, or a material manufactured especially for this purpose, shall be applied to the entire surface. The surface shall be smooth and free of tool marks and ridges. It is recommended that the prepared surface be coated with a drywall primer prior to the application of finish paint.
Usage: The skim coat is a final leveling agent suitable to smooth out a surface to be used under the harshest lighting conditions that may otherwise highlight any imperfections under the finished surface. This finish is highly recommended for gloss and entirely non-textured surfaces.
