Repairing a sagging lath and plaster ceiling

LAST UPDATED: 7th January 2023 by The Editorial Team

Repairing a sagging lath and plaster ceiling

Summary: Step by step guide and video showing how to repair a sagging lath and plaster ceiling.

How to repair a sagging lath and plaster ceiling

If sagging occurs over a large area it would be best to pull the ceiling down and replace it (see section on removing a lath and plaster ceiling).

The timber prop (deadman) supports the sagging area of ceiling while you work.
The timber prop (deadman) supports the sagging area of ceiling while you work.

Repairing the lath and plaster

Small areas of sagging can be repaired in the following fashion:

  • Nail a square piece of chipboard or plywood to the end of a timber prop that reaches from floor to ceiling (this is known as a deadman). Wedge the prop between the floor and ceiling with the plywood or chipboard supporting the sagging area of ceiling.
  • To repair the plaster you need to gain access to the ceiling from above. An upper floor ceiling can be reached from the loft, while a lower floor ceiling will require you to lift the floorboards in the room above.
  • Thoroughly clear away the dust and debris between the joists in the area above the sagging ceiling.
  • Mix up a quantity of fairly runny bonding plaster and pour it over the sagging area. When the plaster dries it should bond the ceiling plaster to the laths.
  • The supporting prop must be left in place until the plaster dries. 
  • Alternatively, you can cut away the sagging area and patch it with a piece of plasterboard the same size as the hole you have created. But it is important to remember when removing the area of sagging ceiling that you will need to expose the ceiling joists to provide fixing points for the plasterboard. See the video below on how to do this.

Having nailed the plasterboard in position, mix a small amount of finishing plaster and apply it to the repair ensuring you tie it in with the original ceiling plaster.

Tools needed

  • Deadman prop
  • Plastering trowel

Materials needed

  • Bonding plaster
  • Plasterboard
  • Galvanised plasterboard nails
  • Finishing plaster

How to repair lath plaster ceiling video

Author

The Editorial Team

The Editorial Team at lets-do-diy.com are a team of experts led by Mark Wilson. We have been creating DIY projects, articles, costs guides and product reviews since 2008. For more info see our about page.