If you have plaster walls in decent shape, repair them. Don’t tear them out just because drywall is more familiar. The National Park Service’s Preservation Brief 21 on flat plaster says cosmetic damage from minor building movement, holes and bowed areas can be repaired without wholesale demolition. It also says hairline cracks aren’t a serious concern as long as the plaster around them is sound. Replace sections only where moisture, structural movement or loose plaster mean a repair can’t restore the wall.
How the two walls are built
- Traditional plaster: usually two or three coats troweled over wood lath, metal lath or gypsum “rock lath.” The plaster pushes through gaps in the lath and forms “keys” that hold it in place.
- Drywall (gypsum board): paper-faced panels screwed or nailed to the framing, with taped and finished joints.
- Veneer plaster: a thin coat of plaster over special gypsum board. NPS describes it as the closer replacement when historic plaster can’t be saved.
Houses often mix systems after past remodels, so age alone doesn’t tell you what’s behind a given wall. Don’t cut into an unknown wall to find out. Older paint and materials may contain lead or asbestos, so follow EPA’s lead-safe practices and get testing before you sand, cut or demolish.
Match the repair to the damage
| What you see | Plaster approach (NPS Brief 21) | Drywall approach |
|---|---|---|
| Hairline crack, sound plaster | Fill with patching material | Fill and refinish the joint or crack |
| Crack that reopens seasonally | Widen slightly, fill, and bridge with fiberglass mesh tape and joint compound if it keeps returning | Retape the joint |
| Large crack from structural movement | Fix the structure first, then cut back about 6 inches each side, add metal lath and replaster | Fix the cause, then replace or reinforce the damaged board |
| Small hole | Basecoat, then a finish coat; one-coat patches tend to look concave once painted | Patch with backing; USG repair clips support a new board piece |
| Loose or sagging ceiling plaster | If the area around it is sound, reattach with screws and plaster washers | Refasten or replace the board |
| Water-stained or soft material | Stop the leak first; NPS says repairs over a wet base will fail again | Stop the leak, dry out, and replace damaged board |
A sagging ceiling is a safety issue. Keep people out from under it and get it assessed promptly. If a crack seems to be getting wider, NPS advises consulting a structural engineer.
When replacement makes sense
Replace when large areas have lost their keys, the lath has deteriorated, or moisture has ruined the base. Factor in what a change in wall thickness does to trim, window and door casings, and electrical boxes. Also budget for dust containment, disposal and painting. Historic or designated properties may need approval first.
Plaster repair is skilled work. NPS notes that owners can handle minor repairs, but bigger jobs usually need a plasterer. Ask any contractor what will stay, what comes out, how they’ll restore support, and how they’ll match the finish.