How to Repair Sagging Plaster & Lath Ceiling

If an entire plaster ceiling is sagging because of water damage, it will likely have to be completely replaced. However, if the sagging area is limited to 1 or 2 square feet, you can remove the old plaster and replace it with joint compound, a form of plaster used with modern drywall. The trick to repairing sagging plaster is to get the underlying lath resecured, as it has to hold the new joint compound.

Tarp
Stepladder
Hammer
Short lath nails
Drywall knife
Joint compound
Paper drywall tape
Drywall sander

Instructions

- 1
  Clear the furniture from the room. Lay out tarps under the damaged area. Climb the ladder, and take a hammer with you.
- 2
  Tap gently at the sagging plaster with the side of the hammer, not the head. Knock down all the plaster that will come down with gentle taps. Leave the lath in place.
- 3
  Use short lath nails and the hammer to resecure any of the lath that has come loose from the ceiling joists.
- 4
  Spread joint compound over the exposed lath, using a drywall knife. Make the compound very thin --- 1/4 to 3/8 inch --- so it just covers the lath and is entirely within the exposed area.
- 5
  Rip off pieces of drywall tape to fit within the damaged area side by side, embedding them in the joint compound. Cover the compound completely with tape.
- 6
  Let the compound set for eight hours. Spread on a second coat of compound over the drywall tape, making it ¼- to 3/8-inch thick.
- 7
  Allow the plaster to dry for eight hours. Apply a third layer over the previous layer. Repeat, adding layers of compound and letting each layer dry until you've built out the repaired area so it's even with the ceiling.
- 8
  Spread the final layer of compound over the whole area and onto a few inches of the surrounding undamaged plaster, getting it flat and smooth.
- 9
  Let the compound dry for 12 hours. Sand it smooth. Repaint.

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