How to Patch a Plaster and Lath Ceiling | Ask This Old House

19August 2018


Ask This Old House general contractor Tom Silva helps a homeowner repair a cracked plaster ceiling in an older home.
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Cost: $200-300

Skill Level: Moderate

Tools List for Patching a Plaster Ceiling:
Drill/Driver
Putty Knife
Mixing Paddle Bit
Hawk
Trowel

Shopping List:
Staging
Drop Cloths
1x3 strapping
3” screws
Drywall Screws
Plaster Washers
3/8” Drywall
Veneer Plaster
Joint Compound
Fiberglass Screen
Felt Pad

Steps:
1. When originally installed, wood lathe was nailed to the ceiling joists. Plaster mixed with horse hair or goat hair was then forced onto the lathe, forming a key that holds it to the lathe.
2. One option is to cut out the damaged area and install a 3⁄8” thick sheet of blue board and plaster.
3. Cover the work area with drop cloths and work off of a rolling scaffolding platform, which can be rented or purchased.
4. Use a drill/driver to secure a piece of 1x3 strapping to the structure above the ceiling. Repeat this process several times in the area of the cracks.
5. For areas where there is no structure above, attach a piece of strapping perpendicular to the others and insert filler pieces of strapping in the gaps between the strapping. Slowly tighten the perpendicular piece.
6. Use a drywall screw with a plaster washer to resecure the damaged sections of plaster to the lathe.
7. Remove the strapping.
8. For areas where the washers don’t hold or the plaster is very damaged, cut out the plaster and create a patch using drywall. Secure the patch with 1 5⁄8” drywall screws.
9. Scrape away any loose veneer.
10. Mix a batch of plaster and joint compound to ensure good adhesion.
11. Place the plaster mix on a hawk and trowel it over the damaged areas.
12. To keep the plaster from cracking and to hide the screws, set a fiberglass screen into the first coat of plaster.
13. After the first coat sets, apply a second coat, filling any voids.
14. Use a felt pad to finish the job and smooth out the ceiling.

Resources:
The ceiling washers, drywall board, plaster, joint compound, fiberglass window screen, trowel, 13x13 inch magnesium hawk, and felt pad brush can be found at home centers and hardware stores.

About Ask This Old House TV:
Homeowners have a virtual truckload of questions for us on smaller projects, and we're ready to answer. Ask This Old House solves the steady stream of home improvement problems faced by our viewers—and we make house calls! Ask This Old House features some familiar faces from This Old House, including Kevin O'Connor, general contractor Tom Silva, plumbing and heating expert Richard Trethewey, and landscape contractor Roger Cook.

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How to Patch a Plaster and Lath Ceiling | Ask This Old House
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