Wallboard or drywall above the shower crumbles due to excessive exposure to moisture. The crumbling area and a small amount of drywall around it will have to be replaced to fix it. Use cement backer board to replace the damaged section of drywall as opposed to green board or regular drywall. Cement backer board is waterproof. Green board is only water resistant, and regular drywall has no water resistance at all.
Instructions
1. Break away the crumbling drywall by hand. Determine where the wall studs are located on either side of the hole in the drywall. Use a stud finder if the are not visible. Make a pencil mark on the drywall at the center of the wall studs on either side of the hole.
2. Use a straight edge and pencil to draw a rectangular or square shape where the drywall will be cut. Extend the hole from the center of one wall stud to the center of the next stud. Draw the top and bottom lines above and below the damaged area. Make sure the square or rectangle is on good, firm drywall.
3. Cut the square or rectangle out with a utility knife, drywall saw or plunge saw. Make sure there are no wires directly behind the drywall and be careful not to cut into the wall studs.
4. Measure the thickness of the old drywall. Purchase cement backer board that is the same thickness as the drywall.
5. Cut a piece of board that is 1/8 to 1/4 inch smaller than the hole in the drywall. Use the straight edge and pencil to indicate where the backer board needs to be cut. Run a utility knife along the lines on both sides of the backer board to cut the mesh and then score the board and snap the excess pieces off by hand.
6. Set the backer board in place and drive screws or nails through the backer board into the wall studs at each corner. Drive another screw or nail through the backer board into the wall stud halfway between the corners if the hole was taller than 8 inches. Some types of cement backer board have a rough side and a smooth side. Install the backer board with the smooth side out if it will be painted. Install it with the rough side out if the area is to be tiled.
7. Stir the joint compound and add water if necessary until it has a creamy texture. Use a putty knife to apply joint compound along the edges of the backer board and drywall to seal the gap. Place mesh joint tape along the edges and smooth it into the joint compound with the putty knife. Apply another layer of joint compound over the tape.
8. Do not apply the joint compound too thick. There should be approximately 1/16 inch of joint compound underneath and on top of the tape. Sand the joint compound smooth after it dries. Seal the bottom edge of the cement backer board with silicone caulk if it is installed directly above the shower tile or fiberglass wall panels.
Tags: backer board, joint compound, wall studs, cement backer, cement backer board, into wall, along edges