Bathrooms require specific materials to withstand the high moisture environment of bathtubs, sinks and showers. Bathroom drywall or cement board which should be used? Ordinary wallboard or drywall becomes soft and spongy in damp settings. It should be avoided for bathroom walls.
Bathrooms require moisture-resistant wallboard, cement board or “Greenboard”. Moisture-resistant Greenboard gets its name from the green tinted, water-resistant paper covering. At the core it is saturated with asphalt to resist absorption and softening. Apply Greenboard on all bathroom walls and surfaces, which will later support tile. Do not use green board on bathroom ceilings. It has a tendency to sag.
Calculate how many 4-foot by 8-foot sheets will be needed and purchase 10% to 20% extra for cutting errors and breakage.
Always check the local building department for the city’s construction code requirements. Building departments should be able to provide a copy of the local codes for drywall installation, taping and required spacing of drywall screws or nails.
1. Cut and fit Greenboard
Score through the surface skin of the cement board and the mesh underneath with a utility knife. This may require several cuts. 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.
Greenboard should be secured in place using 1-1/2” galvanized roofing nails or with special screws called wafer-head fasteners. Space the nails or screws no more than 8” apart. All cut edges should be coated with a manufacturer approved water-resistant adhesive.
2. Showers and tubs
Greenboard sheets should be attached to wall studs horizontally in the same manner as regular wallboard. In bathtubs and showers, maintain a 1/4” space between the lower paperbound edges of the Greenboard and the bathtub or shower pan. A bead of water-resistant adhesive must 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.
It is important to use a manufacturer approved sealant and adhesive. Do not use joint compound over joints and fasteners around showers and tubs.
3. Sheet the bathroom walls
Install the drywall sheets horizontally. To begin, measure the first wall to stud nearest the end of the drywall sheet. Be certain the end joint falls across the center of a stud to provide the strongest joint. Measure the first Greenboard sheet, cut to fit with a utility knife or circular saw. Also, carefully measure for any cutouts such as light boxes, pipes, vents or outlets and remove these with a utility knife or saber saw. Stagger greenboard end joint to avoid cracking.
Begin at the center of the first sheet and apply screws every 8” along each stud, sinking the heads just below the surface. Carefully set the screw depth to not tear the paper. The screws around each edge of the drywall sheet should be placed 3/8” to ½” from the edge of the sheet. Work around the room and finish sheeting the remaining walls.
Apply metal corner beads or pre-finished rounded corners at this time.
4. Tape and mud
Double check each screw and nail. They should be below the surface of the drywall. It is easier to adjust the depth now rather than after you’ve started to tape and mud.
Use a 4” putty knife to cover each screw or nail dimple with joint compound, keep the surface flush with the drywall. With a 6” putty knife, run it along each seam of the drywall to fill each crease with joint compound and 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” knife and remove any extra joint compound.
Allow the first coat to dry and then apply a second coat of joint compound feathering the edges to 4” on each side of tapped joints. Wait for the second coat to dry and apply the third coat, feathering it wider to 7” or 8” on each side of the joint. Typically, the third coat is a very light skim coat, spread out with a 12” or 14” finishing knife. When it’s dry, finish sand with 100-grit or 120 grit sandpaper. I recommend using goggles and a dust mask when sanding. Gypsum dust and joint compound dust are an irritant to eyes and throat. Sand only the joint compound, not on the paper. If you scuff the paper, it will be necessary to add a very thin coat of joint compound over the areas scuffed. Smooth or finish sand as needed.
Now the bathroom is ready for paint and tile.
5. Tools for a bathroom project
Check your toolbox and add any tools needed.
Soft lead pencil
12 to 25 foot tape measure
48-inch drywall T-square
Utility knife with extra blades
Electric screwdriver with drywall bit
4” and 6” putty knife
Small hand-held or palm size rasp
Optional tools that will help move the project faster: saber saw, 12” or wider finishing knife, circle cutter and a small drywall router with a carbide tip.
6. Correct drywall tools save time
A tape measure with a finger lock will hold the tape at the measured distance. Drywall hammers have a serrated face made specifically to keep the hammer on the nail head. Electric screwdrivers, with a magnetic screw-holding tip will release the drywall screw when it has reached the proper depth on the drywall sheet. Hand-held Sureform® rasps or planes are handy for reducing and straightening cut edges of Greenboard or drywall pieces.