Fixing a plaster ceiling that is cracking is a messy job but not that difficult. Sometimes there is an underlying moisture problem or leak that has to be addressed, but since most plaster ceilings are quite old, the culprit is often merely age. The secret to lasting repairs on plaster cracks is using drywall tape instead of covering them with spackle or joint compound.
- Skill level:
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Things you need
- Plastic sheeting or dust sheets
- Chisel or stiff-bladed putty knife
- Paper drywall tape
- All purpose joint compound (mud)
- Mud pan
- 6-inch and 10-inch drywall knives
- Sanding sponge or drywall sanding tool
Cover the work area with plastic sheeting or dust sheets. If possible, move furniture out of the room, or out from under where you'll be working.
Scrape loose material out of the cracks with the corner of the chisel or stiff putty knife. Ideally you want a little groove where the crack is.
Use all purpose joint compound instead of topping compound because it is a little harder and more flexible. Put some in the mud pan, and using a 6-inch knife, lay a smooth bed of mud over the crack. Do your best to keep the crack in the middle of the mud line, and make sure there are no bare spots as these will cause the tape to bubble up later.
Lay the tape along the centre of the mud line. Quite often, cracks in plaster will zig and zag instead of being straight. Cut or tear the tape in the right lengths to cover the entire crack.
Holding one end of the tape in place so it doesn't slip and slide, use the knife to smooth and embed it firmly in the mud. Do your best to remove lumps and ridges of excess material without disturbing the tape. Let this dry for a day or overnight before the second coat. Once it is dry, and before applying the second coat of mud, you can knock down lumps and ridges.
Using the 10-inch drywall knife, apply a second coat of mud over the repairs. The wider application will allow for a more seamless blend with the surrounding surface. Since this is a thinner coat, it will take four to eight hours to dry. If you are matching a texture over the repair, two coats will be plenty. Once dry you can sand it smooth and do the texture. If your ceiling is smooth, you will need to do a third light coat of mud to look really good.
Apply the third coat, feathering out the edges as best you can. Remember, the smoother your application, the less sanding you will need to do later on. Let dry four to eight hours or overnight.
Sand the repair smooth using sandpaper over a drywall sanding tool or a sanding sponge. Work in the best light possible, and use your hand to check for imperfections. Quite often it is easier to feel uneven surfaces than see them. Once sanded smooth, dust off the ceiling and roll a coat of primer over the repairs before repainting.
Tips and warnings
- If large sections of the ceiling are falling or sagging with extensive damage, more work is needed.
- For cracks that appear right at the juncture of wall and ceiling, a good paintable silicone caulk will work quite well.
- Never put unused mud back into the original bucket, because you can contaminate it with dried material. Dispose of it into a dustbin or bag, not down the sink.