How do I Repair Plaster Ceiling Damage in a Bathroom?

Mark around the damaged area with your pencil and square. Make the marks a perfect square, with two opposite sides running through the middle of ceiling joists. If there isn't enough missing plaster to ascertain exactly where the joists are, pull some plaster down so you can.

Use a jigsaw to cut along the marked-out lines, cutting out the square. The joists should be half-exposed on two opposite sides.

Measure the dimensions of the square and transfer them to your piece of wetrock. Use your utility knife to score the wetrock at the lines and snap it. Cut along the inside of the lines, rather than the outside, so the piece will be a little smaller than the hole.

Lift the square piece up to the ceiling and set it in the hole. Drive in galvanized screws every 6 inches along the edges and through the joists. If there are additional joists behind the piece, drive screws in them as well.

Lay strips of mesh adhesive drywall tape around the perimeter of the patch, covering all the seams between the patch and the rest of the ceiling.

Spread joint compound over the tape with your 4-inch drywall knife. Cover the tape completely, and make the compound smooth and flat.

Let the compound dry for six to eight hours. Apply a second layer of joint compound, making it slightly wider than the previous layer. Repeat the process for a third layer.

Let the third layer dry for a full day, then sand it smooth with a sanding pad. The ceiling is now ready for repainting.