Water does not mix well with plaster walls or ceilings. Water damage can happen because of roof leaks seeping down onto the ceiling and into the wall, an overflowing or leaking toilet or bathtub, shower leaks, washing machine line leaks, dishwasher leaks, water heater leaks and basically anything else in a home that uses water. Water damaged plaster walls and ceiling need to be taken care of immediately in order to avoid falling walls or ceilings which is dangerous or something even more dangerous such as the growth of toxic black mold.
Remove Damaged Walls and Ceilings
Buy washers and screws made for plaster facades at a hardware store or home improvement store.
Screw in screws and washers every 5 to 6 inches around the wet plaster onto the dry part. If the plaster has already dried, measure 12 inches from the water stain and secure in screws and washers. Using screws and washers will hold the portion of the ceiling or wall that has not been damaged in place and keep it from falling. When securing screws make a squared off pattern around the water damage.
Drill holes into the plaster about 1/2 of an inch away from each other. Drill the holes in a straight line just inside the square pattern made by the screws.
Use a chisel pointed towards the damage the break the plaster out from between the holes and gently tap it to carefully crack and break plaster while forming a straight line.
Gently tap off stuck on plaster from the lath.
Wire brush small stuck on plaster pieces to remove them.
Inspect the Lath Behind the Plaster
Look for any mold growth on the wet lath. If you see any mold growth on the lath, spray it with bleach and clean it off. Make sure you wear protective eye glasses, gloves and a mask. If the mold extends behind the undamaged plaster, you will have to extend the perimeter of screws and washers and remove the plaster until you get to an area that has no mold or mildew growth.
Be sure to let the lath and wood dry completely for at least one week before covering it and continuing.
Patching the Plaster Wall and Ceilings
Measure the thickness of the plaster and buy drywall in the same thickness or slightly thinner than the thickness of the plaster. Drywall is available in many size and thickness at hardware stores, home improvement stores and building supply stores.
Cut the drywall in the exact same size as the area with exposed lath.
Use drywall screws to secure the patch to the lath every 5 to 6 inches around the edge of the patch. Place screws into drywall and fasten it to wall studs or floor joists every 4 to 5 inches.
Use self stick fiberglass mesh tape and place it along the seams of the drywall.
Apply a very thin layer of joint compound over the self stick fiberglass mesh tape and over the screws with a spackle knife.
Allow the joint compound to dry completely.
Spread another thin layer of joint compound over the first, extending it past the fiberglass tape and feather it out and the edges.
If the ceiling or wall has a design in the stucco, spread joint compound over the whole drywall patch and while it is still wet create the same design as the existing wall or ceiling to match it. If there is a circular design, use a paint brush and dry circles all over the patched area. If there is a rough texture design press the paint brush into the wet joint compound and dab at the patch. If the design is smooth and swirled use a trowel to move in a circular motion over the area. If the wall or ceiling texture is smooth, use a fine grit sandpaper to smooth out the surface after the joint compound has completely dried.
Prime the patched area and then paint it to finish.