Q. Patching Plaster
The punch list for a remodeling job that I am doing on an 1880s house includes a few small plaster repairs. The damaged areas are small — about the size of a hand — and they are not in a prominent area, so I feel confident that I can tackle them myself without calling in a specialty subcontractor. What’s the easiest way to patch small holes in plaster?
A. Contributing editor Tom O’Brien, a carpenter in New Milford, Conn., responds: First, make sure the surrounding plaster is firmly attached to the lath. If the plaster surface is sound but gives under pressure, I use plaster washers from Charles St. Supply Co. (charlesstsupply.com) to anchor it firmly to the lath and the studs.
An alternative is to drill 1/4-inch holes through the plaster (but not the lath), inject construction adhesive into the holes, and then apply pressure to the entire area with a braced piece of plywood (such as a concrete form) until the adhesive has cured.
Drywall makes a good plaster-patching material, but since plaster thickness is never consistent, it’s always good to have some scraps of 1/4-inch and 3/8-inch on hand; 1/2-inch drywall might be too thick. Once I’ve removed the damaged plaster and stabilized the surrounding area, I cut the drywall patch to size and screw it to the wood lath. Then I tape the patch with fiberglass mesh tape, and mud the repaired area with a setting-type joint compound, such as Durabond 45 (usg.com). After the setting compound has hardened, I feather out the repair with one or two thin coats of lightweight joint compound.
For very small holes with good lath backing, you could skip the drywall patch and just use setting compound, or mix up a batch of hardware-store-variety plaster. If you do use actual plaster, keep in mind that you won’t be able to sand it afterward, so you’ll need some basic trowel skills. If there are cracks, I use an old 5-in-1 tool or a bottle-opener to flare them out, and then mist them with water before spreading the setting compound.