Drywall Finishing Materials and Techniques
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Drywall Sheets
Drywall sheets consist of a gypsum core, sandwiched between two sheets of heavy paper. The paper is wrapped around the gypsum to form two finished edges.
Drywall sheets are commonly available in 4ft x 8ft and 4ft x 12ft pieces with thicknesses of 3|8th, 1|2 and 5|8 inches. Drywall available at your local home store includes three basic types: standard drywall, fire retardant and moisture resistant drywall. Some building codes require fire retardant drywall on ceilings and moisture resistant drywall is used in bathrooms and kitchens to standup to the high humidity in these rooms.
The finished edges on drywall are compressed, so when two sheets are placed, finished–edge to finished–edge, a small depression is formed. The seams between the sheets are taped with drywall tape and the depression is filled with joint compound or mud, to create a flat, smooth, finished surface.
Drywall Finishing Tools
Tools for applying drywall joint compound include a mud pan and joint knife. Mud pans are available in plastic and stainless steel. The metal pan is the best choice for keeping the knife blade clean. Plastic pans have a metal strip embedded in the rim that can easily become clogged and they tend to fall out and rust.
Drywall joint knives are available with varying flexibility. A medium flexible blade is the best choice for drywall work. If the blade is too flexible, it can bow when finishing seams causing a dip in the finished joints. If the blade is too stiff it can be impossible to smooth the surface of the mud when skimming.
Drywall Joint Tape and Corner Bead
Flat drywall seams can be finished with paper tape or self–sticking, fiberglass mesh tape. Paper tape should be applied with plenty of joint compound and stuck down tightly or it will probably come free easily. The mesh tape can be easier to use and it may require fewer coats of mud to finish the seams using this method. The tape should be lightly sanded after the first coat of joint compound to knockdown the fibers and make the joint easier to smooth out. Outside drywall corners can be finished with metal or paper drywall corner bead. Metal corner bead is the best choice in most cases for a square, durable corner.
Drywall Joint Compound
It's best to always use ready–mixed joint compound or mud, for finishing drywall seams and inside corners, setting–type joint compound will harden too quickly in most cases, causing problems. One exception to this is finishing metal corner bead where a thick first coat is required. In these cases, setting compound will not shrink like ready–mixed and it is much harder when set, so it makes a very durable corner.
Don't try to use a light joint compound for finishing drywall seams or corners. Light joint compounds are manufactured to be easy to sand. To achieve this the hardness and strength of the mud is sacrificed. In addition, light compounds tend to pull away from surfaces when applying a thin coat such as when finishing drywall seams and skim coating.
Handling Joint Compound
Use a small joint knife of about 6 inches for the first coat or two of joint compound on seams and inside drywall corners. A larger knife is good when first coating metal corner bead and for the finish coat on flat seams and inside corners.
To handle and apply mud, scoop some into a mud pan and collect a portion onto the rim. From the rim, work the mud onto the wall, a little at a time to cover seams and corners. See Skim Coating Techniques for more on handling joint compound.
