Used in high moisture areas such as the bathroom, laundry room or kitchen, greenboard is designed to resist water damage. It is installed the same way as drywall: hung on walls that will eventually be tiled, behind shower and tub surrounds and around the sink in the kitchen. In the bathroom and laundry room it should be used throughout. Greenboard uses fiberglass to sandwich in the gypsum core unlike drywall which has paper outer layers. This makes greenboard ideally suited to areas where moisture will eventually rot traditional drywall.
Obtain the Materials and Tools
To install greenboard, you need the same tools as you would for hanging drywall. These include a utility knife, tape measure, T-square, sanding block, power drill, hammer, chalk line, drywall knives and a drywall trough. Materials include ½ or 5/8-inch greenboard, drywall screws, fiber drywall tape and all purpose drywall compound. Once you have everything, it is time to begin.
Greenboard usually comes in 3x5-foot sheets. When hanging it, start from the floor and work up. Hang it vertically so the joints you have to work with end up as bevel joints. These are much easier to finish after the hanging is complete. Hang as many full sheets as you can before making cuts to accommodate smaller spaces. If it helps, snap a chalk line onto the greenboard to indicate exactly where each stud is when you hang it. Hold the sheet in position, measure the placement of the studs and mark the spacing on the board. Then snap the chalk lines. This helps to make screw insertion easier.
When assembling a joint between two adjacent sheets of greenboard, make sure the abutting edges share a stud. Joints should never be made over empty space. Cut the greenboard lengthwise if you have to, otherwise your joints will end up weak.
Cutting to Size and Fixtures
Encountering smaller areas where full sheets will not fit, you must cut the greenboard down to size. Measure the dimension of the area twice, use your tape measure or T-square to mark the board and score the line(s) with the utility knife. Break the gypsum core, then cut through the paper on the opposite side. Sand cut edges with a sanding block.
To cut holes for fixtures, measure the distance to the fixture from the next board over and up or down from the floor or ceiling. Mark its position on the sheet, drawing the shape of the cut on it. Use a compass to make circular marks. Double check your measurements and score the lines. Once scored, make an X with the knife through the portion to be cut out then tap it with a hammer. Sand the inside edges.
When inserting screws, always work from the center of the sheet out to the edges. Set a drywall screw every 6-8 inches on every stud and into any headers or cross pieces as well.
When finishing the joints, the level required will be determined by what will eventually cover the greenboard. If it is to be covered with texture, primer and paint, you need a higher level of finish which means one coat of mud over the joints to adhere the tape followed by two more coats of mud. Use all purpose drywall mud. If tile or a surround will cover the greenboard, you only need a level 1 or 2 finish. That means one coat of mud, tape and a second quick coat of mud. Use water resistant fiber drywall tape.
Hanging greenboard is practically the same as traditional drywall. The difference is where it is installed. In high moisture areas where water vapor will eventually ruin drywall, greenboard is necessary.