Things You'll Need
Piece of drywall
6-inch drywall knife
Drywall never looks the same after being damaged by water, even if it is painted after it dries. When the bottom of the drywall receives water damage, you must repair it to avoid a mold problem. The damaged drywall must be removed and new drywall put in its place. Even someone inexperienced in home repair can complete this repair by following a procedure that is designed for a successful outcome every time. The repair takes a couple of days, including drying time.
Cut off the affected area of drywall using a utility knife. Cut off as much drywall as it takes to leave only good solid drywall. Cut enough to expose wall studs beyond the damaged area. This will make it easier to install a new piece of drywall.
Measure the length and width of the area of the wall that needs new drywall. Lay the drywall on a flat, hard surface with the paper side up. With a utility knife, cut out a piece of drywall from a new piece the size you need based on your measurements.
Fit the cut piece of drywall into the damaged area. Secure it to the wall studs using drywall screws and an electric drill with a driver bit.
Place mesh tape evenly over all the joints. Ensure the tape is flat and is wrinkle free.
Fill a drywall pan with joint compound. Scoop some joint compound out of the pan with a 6-inch drywall knife so the end of the knife has a bead of compound on it.
Smooth the joint compound over the taped areas. Use the drywall knife at a 45-degree angle to the wall to spread the joint compound over the joints in a downward motion. Make the compound as smooth as possible and feather the edges with the very edge of the knife. Allow the joint compound 24 hours to dry.
Sand the joints with a sanding sponge to smooth out any ridges or high areas. Apply a second coat of joint compound and sand again after it dries.
Paint the repaired area with matching paint and a paint brush.