Repairing Leaking Drywall

Cut out the leaking section of drywall to expose the underlying problem. Insert the keyhole saw into the drywall, apply pressure and cut out a roughly square section around the wet portion. Cut the drywall from stud to stud on walls or joist to joist on ceilings. Repair whatever damage exists behind the drywall from leaking shingles and pipes or other sources.

Remove half of the drywall on the stud or joist so you expose half of the wood and allow for the new section of drywall to have an area on which to be mounted. Cut away the drywall with a utility knife to expose part of the wood beneath -- or the metal stud, depending on your home's construction.

Measure and cut a new piece of drywall to fit into the area. Use the tape measure and pencil to mark your piece of drywall. Place the board in a vertical position, leaned up against a wall. Hold the T-square against the drywall as a cutting guide and slice the front of the drywall with a utility knife along your line. Apply pressure to snap the board across your scored mark, and cut the back side of the board once it is folded to remove your cut section. Repeat this cutting process for all the sides of your piece.

Mount your new piece of drywall and finish it off. Screw it into place along the studs or joists with a drill and screws. Cover the joints between the old piece and the new piece with a layer of mesh tape. Apply drywall mud to the tape with your drywall taping blade. Smooth the mud over the tape, allow the mud to dry for at least 24 hours and then apply your chosen finish, such as paint, tile, wallpaper or wood paneling.