Dealing with Wallboard
Wallboard, also known as drywall or gypsum board, is one of the most common wall materials. Panels — generally 43 × 83 in size — consist of an inner layer of gypsum plaster that's covered on both sides by strong paper. The panels are nailed, screwed, or glued to the wood studs that form the inner framework of the wall, and their seams are sealed with tape and joint compound, so that when you look at a wallboard wall, you shouldn't be able to tell where the panels meet. If you're using wallboard in a damp location, such as a bathroom, it should be water-resistant (often referred to as greenboard, for its color), as should the joint compound you use.
Very small holes or shallow gouges that aren't cracked can be fixed with a quick layer of lightweight joint compound (sold as a powder that you mix with water, or as an easier-to-use ready-mixed product) applied with a putty or taping knife that's slightly wider than the area you're working with (generally 4 inches wide). Let the compound dry, sand it level with the wall surface, and prime/paint to match the wall.
Small cracks and medium-sized holes (like those created by a door handle) can be fixed with self-adhesive mesh tape or screening and joint compound. Bigger holes-those larger than 5 inches across-may need the added strength of a wallboard patch. Your first step in both cases is to clean up the crack or hole by removing loose pieces of wallboard and brushing away any grit or dust particles.
For the tape/screen method, cut the tape/screen to fit, allowing about 2 inches of extra material on all four sides. Peel the backing away from the adhesive surface, and stick the tape or mesh screening over the hole or crack, pressing it down firmly and smoothing it out to keep it free of creases or bubbles. Using a 4-inch putty or taping knife, apply a layer of joint compound to the wall over the tape or screening, spreading it downward and diagonally as you cover the area. Let it dry (usually eight to twenty-four hours, but check your product instructions).
Once the joint compound is dry, sand it lightly with 100-grit sandpaper, being careful to sand only the compound, not the wallboard itself. Apply a thin coat of compound with a 6-inch putty or taping knife, feathering it out on the edges to form a smooth transition to the wall. When that's dry, sand it lightly with 150-grit sandpaper and apply a very thin finish coat of compound with a 10-inch knife. The compound should extend to two or three times the size of the original hole or patch. Let it dry, sand again with the 150-grit sandpaper, and then paint with primer and a finish coat to match the wall. (You may be able to get away with two, rather than three, coats of joint compound, but keep in mind that three thin coats of compound will provide a much cleaner repair than one or two thicker coats.)
Sanding the joint compound when it's dry creates a lot of fine, messy dust. Using a dampened sanding sponge will give you a smooth finish while significantly reducing the dust flying around. Always use a dust mask while sanding, to avoid inhaling the dust, and wear eye protection.
For holes larger than 5 inches across, use 1- to 2-inch-wide strips of scrap wood or wallboard as a backing plate for a wallboard patch. Insert them through the hole, and fasten them with wallboard screws or glue so that they span the back of the hole.
Strips of wood used as backing plates behind a wallboard patch give it stability.
If you're lucky enough to still have the piece of wallboard that came out of the hole, you can use it as a patch. Brush off loose particles, coat the edges and back with joint compound, and insert it into the hole against the backing plate. You can also glue the patch against the backing plate with a hot-glue gun, if you find that's easier.
If you don't have the missing wallboard-it often falls into the wall-cut the hole into a square or rectangle using a wallboard saw or sturdy utility knife before inserting the backing plates. Cut a piece of scrap wallboard into a patch that is slightly smaller than the piece you removed. Coat and insert as previously described.
Once the patch is in place, apply joint compound as you would for a tape or mesh screen repair. When you're smoothing the first coat of joint compound into the patch's seams, hold the putty knife at a 45-degree angle to the wall. This helps to force the compound into the seam.
If the hole was caused by a doorknob, don't forget to install a doorstop to prevent it from happening again. The type that slips over a hinge pin is effective, and it's usually less intrusive than the spring-type that screws onto a baseboard (toddlers and puppies love playing with the latter).
Wallboard installed with screws will reduce the incidence of “nail pops” appearing in the wallboard's painted or wallpapered surface later on. Because screws are more time consuming to install than nails, however, nails are often used, leaving homeowners to deal with the annoying little paint cracks or circles coming off over the top of the nails.
To fix nail pops, drive the nail back into the wallboard if it's still snug in its nail hole. If it's not, remove it. In either case, insert a screw through the wallboard and into the same stud that the nail went into, about 2 inches from the popped nail. The screw should create a “dimple” in the wallboard, so that its head is slightly lower than the wallboard surface, without tearing the wallboard paper.
Cover the popped nail's head or hole and the screw head with three layers of joint compound, as detailed previously for repairing wallboard.
Repairing wallboard sometimes isn't enough, especially if you have an area of water damage-in a flooded basement, for example-that has to be cut out. In this case, you'll need to replace the wallboard. This isn't a difficult job, but it's time consuming because you have to wait for the joint compound to dry, and it can be messy when you're sanding; the joint compound dust is so fine that it seems to go everywhere.
Here's how to calculate the quantity of materials you'll need for a small area:
Wallboard: measure the wall surfaces to find the area in square feet, add 15 percent for mistakes and cuts, and if you're using 4' x 8' sheets of wallboard, divide your total by 32 (the area of the wallboard sheets)
Screws: about ½ pound for each 100 square feet of wallboard
Joint compound: 15 pounds for a 10' x 8' area
Joint tape: 60 to 75 feet for a 10' x 8' area
To cut new wallboard, mark the cutting line on the face of the wallboard, then score the paper along the line with a utility knife (running the knife blade against a level or straightedge makes this easier). Lift the board up, and snap it by sharply banging the reverse side of the board so it breaks along the line that you've cut and folds toward its reverse side. Cut through the paper on the reverse side along the fold to prevent the paper from tearing. (This should form a clean edge, but you can also sand any rough edges to create smoother joints if necessary.)
To install the wallboard, work from the ceiling downward. Use nails to tack up the sheets, and then fasten them securely with screws every 6 inches. (A dimpler drill attachment inserts screws without cutting the paper.) A board lifter or pry bar will keep the bottom piece of wallboard the required l/4 inch off the floor while you fasten it in place. Use L-shaped wallboard pieces around window and door frames; a wallboard joint at the frame corners can crack.
When feathering out the joint compound, apply greater pressure to the outside edge of the knife, spreading the compound more thinly. This results in a seamless finish between joint tape and wallboard.
There are two types of wallboard joints: butt, where the boards' short or cut sides meet; and tapered, where the long sides meet. Butt joints require thin coats of compound; tapered joints need a slightly more generous first coat to build a level surface. For corners, try products such as paper-laminated steel corner bead, which installs with joint compound and is less likely to crack or chip than a regular steel corner bead. You can also buy special taping knives to handle inside and outside corners, which make the process not only easier, but more professional looking as well. Normally, you need three coats of joint compound to effectively coat the joints, but two coats often are enough for inside and outside corners.
Use three progressively larger knives to apply compound, starting with one that's about 4 inches wide. Apply compound to the joint with this narrowest putty knife, covering only as much area as can be worked in three to four minutes (the compound loses adhesion as it dries). Embed a length of joint tape in the compound along the joints using a putty knife. Hold the knife at a 45-degree angle, and draw it along the joint, over the tape, to remove excess compound and eliminate air bubbles. The tape should be level with the face of the wallboard, fully embedded in the compound, with enough compound between the tape and the wallboard to ensure adhesion. Let it dry for eight to twenty-four hours as required, and then sand to a relatively smooth finish with 100-grit sandpaper.
Using a medium-width knife (about 6 inches), apply a second coat of compound to the joint, covering the tape. Feather the edges of the compound about 2 inches beyond the first coat. Let it dry, then sand with 150-grit sandpaper. Use the largest putty knife (about 10 inches) to apply a third coat, again feathering out 2 inches beyond the second coat on each side. Let it dry, then sand with 150-grit sandpaper to a smooth finish. (Note that your nail/screw dimples must also be filled using three coats of compound, but they don't require joint tape.)