How to Repair a Rotted Wall in the Bathroom

Use a pencil and level to mark out a square perimeter around the damaged section. Expand the width of the section enough so that the two vertical sides are running flush alongside the insides of the wall studs at both ends. Cut out the marked section using a jigsaw.

Screw 2x2 boards to the sides of the studs using galvanized screws 2 3/4 inches long. The front edge of each 2x2 should be even with the front edge of the stud (meaning it will be set back from the drywall).

Screw your two plywood scraps behind the drywall at the upper and lower horizontal edges of the hole, using 1 1/2-inch screws. Shoot the screws through the drywall surface while holding the plywood behind it. About half the width of the plywood scraps (about 3 inches) should be exposed at the top and bottom of the hole, with the other half tucked behind the drywall and screwed down from the front.

Measure the dimensions of the hole. Cut a piece of wet-rock to that size, by scoring the surface with your razor knife and bending the piece at the scored line until it breaks.

Set the cut wet-rock into the hole, so it presses against the 2x2s on the vertical edges and the plywood on the horizontal sides. Shoot in drywall screws every six or eight inches around the edges of the wet-rock piece into the wood behind it.

Press drywall tape along the seams around the edges of the patch. Use your drywall knife to cover the tape with a flat layer of joint compound.

Let the compound dry four to six hours. Apply a second coat of joint compound, let it dry, then apply a third coat. Let the third coat dry overnight.

Sand the compound with a pad sander to get it smooth. Repaint the wall.