DIY Bathroom Drywall Installation
Bathrooms present a special challenge because of the high moisture environment of baths and showers. Ordinary wallboard or drywall becomes soft and spongy in damp settings, so it shouldn't be used for bathroom walls. In place of common drywall, use moisture-resistant wallboard, cement board or "greenboard." Moisture-resistant greenboard gets its name from the green-tinted, water-resistant paper on its face. Its core is saturated with asphalt to resist absorption and softening. Apply greenboard on all bathroom walls and surfaces that will later support tile. Do not use greenboard on bathroom ceilings. It has a tendency to sag.
Before you start, check your city's code requirements. Most building departments will be happy to provide a copy of the local codes for drywall installation and nail or screw spacing.
Tools You'll Need
Check your toolbox for the following hardware: soft lead pencil, a 12- to 25-foot tape measure, 48-inch drywall T-square, utility knife with extra blades, keyhole saw, drywall hammer, electric screwdriver with drywall bit, 4-inch and 6-inch putty knives and a small handheld or palm-sized rasp. You may also want to have a circle cutter, electric saber saw, 12-inch or wider finishing knife and a drywall router fitted with a carbide tip.
Proper tools save time during a project. Choose a tape measure with a finger lock to hold the tape at the needed distance. Drywall hammers have a serrated face keeping it on the nail head. An electric screwdriver, with a magnetic screw-holding tip and an adjustable clutch, will release the drywall screw when it has reached the proper depth on the greenboard sheet. Handheld rasps will quickly reduce and straighten the cut edge of greenboard and drywall pieces. This is also handy for fine fitting drywall pieces.
How to Cut and Fit Greenboard
To cut it, score through the surface skin of the cement and the mesh below with a utility knife. This may require several cuts. Then, snap the board along the cut and plane the edge with a rasp. Cement board may also be cut using a circular saw and a carbide-tipped blade. Wear safety goggles and a dust mask. Make any necessary holes by scoring the desired shape into the cement board and then smashing out the marked area with a hammer.
Cement board should be secured in place using 1 1/2-inch galvanized roofing nails or with special screws called wafer-head fasteners. Space the nails or screws no more than 8 inches apart. All cut edges should be coated with a manufacturer-approved water-resistant adhesive.
Showers and Tubs
Greenboard sheets should be attached to wall studs horizontally, the same as with regular wall board. In baths and showers, maintain a 1/4-inch space between the lower paper-bound edge of the greenboard and the tub or shower pan. A bead of water-resistant adhesive should be added across all nail or screw heads, corners and openings where water pipes penetrate the wall. Also seal between the top of the tub and the greenboard.
Always use manufacturer-approved sealant and adhesive, rather than joint compound over joints and fasteners.
Sheet the Walls
Install the sheets horizontally. Measure the first wall to nearest stud. Be certain the end of the sheet falls across the center of a stud. This will strengthen your joint. Measure your first greenboard sheet, and cut to fit with a utility knife or circular saw. Also, measure for any obstructions, such as light boxes, pipes, vents or outlets, and cut these out with a utility knife or saber saw. Stagger each end joint to avoid cracking.
Hold the sheet in position and, beginning at the center of the sheet, apply screws every 8 inches along each stud, sinking the heads just below the surface without tearing the paper. The screws around the edges of the sheet should be not less than 3/8 inch or more than 1/2 inch from the edge of the sheet. Work your way around the room and sheet the remaining walls. If the room requires metal corner beads or pre-finished rounded corners, then apply those now.
Tape and Mud
Check each screw and nail make certain it is below the surface of the drywall. It is easier to adjust the depth now rather than after you've started to tape and mud.
Using a 4-inch putty knife, cover each screw or nail dimple with joint compound, keep the surface flush with the drywall. Run a 6-inch putty knife along each seam of the drywall to fill creases with joint compound. Then, tape the joints. Start at the center and stretch the paper tape along the freshly mudded seam. Smooth the tape into the wet mud with the 6-inch knife and remove the extra joint compound.
Let the first coat dry; then lay a second coat of joint composing over it. Feather 4 inches on each side of the joint edges. Apply a third coat after the second coat of compound has dried, typically a lighter skim coat that can be applied with a 12- or 14-inch finishing knife. Then feather 7 or 8 inches on either side of the joint. Once the compound is dry again, put on goggles and finish sanding with 100- to 120-grit sandpaper. Do not sand the paper, only the joint compound. If you damage the paper, then you may need to float a very thin layer of compound over it.
Now you're ready for paint and tile.