Plaster Wall and Ceiling Repair for Older Homes

How plaster walls are built, and why they crack

Before drywall became standard, most interior walls were plaster troweled over lath in two or three coats. The first coat was pushed through the gaps in the lath, and the blobs that curled over behind it, called keys, are what hold the wall up. As a house settles and moves through humid summers and dry, heated winters, cracks open at the weak points: above doors and windows, at ceiling corners and along stair walls.

A crack on its own is cosmetic. A crack where one side sits higher than the other, a wall that sounds hollow when you tap it, or a ceiling with a soft bulge means the keys have broken and the plaster is coming loose from the lath. That has to be fixed before any crack is filled, or the repair will crack again.

Cracks, keys and loose plaster

For sound plaster with cracks, we cut the crack open slightly, fill it with a setting compound, bridge it with tape or mesh and feather the finish wide so it can't telegraph through paint. For loose plaster we reattach it before patching. Plaster washers, thin perforated metal discs, go in with screws through the plaster into the lath or framing and pull the plaster back tight; they are then skimmed over and disappear under the finish. Where plaster has fallen out or crumbled, we cut back to solid edges and build the hole up in layers to the surface of the wall.

Wood lath, metal lath and rock lath

What sits behind the plaster changes how we repair it. Wood lath, narrow strips nailed across the studs with gaps between them, is typical in the oldest homes in Chevy Chase, Kensington and many DC neighborhoods. Metal lath, an expanded steel mesh, shows up on curved walls, around chimneys, in bathrooms and in later work. Rock lath, also called gypsum lath, is panels of gypsum board that plaster was applied over, common in homes from roughly the 1930s through the 1950s, including many Bethesda colonials and Cape Cods. Rock lath walls can look like drywall from the outside but behave like plaster, so we check before cutting anything.

Sagging plaster ceilings

Ceilings fail first, because gravity is always working on the keys. A ceiling that has dropped slightly but is still in one piece can usually be screwed back up with plaster washers, then the cracks are taped and the whole area skimmed. Ceilings under bathrooms often have a leak in their history; if yours is stained, the source has to be fixed and dry first, and our page on water-damaged ceiling repair explains the order of work. If a ceiling is badly sagging or crumbling, keep people out from under it and call us; we'll tell you plainly whether it can be secured or needs to come down.

Repair, skim coat or replace?

The National Park Service's Preservation Brief 21 on repairing historic flat plaster makes the case for repairing plaster rather than tearing it out, and we agree for most houses. Our usual choices are:

• Repair: cracks and holes in otherwise sound plaster are fixed in place.
• Skim coat: a wall covered in fine cracks or old, uneven patches gets a thin coat over the whole surface for one consistent finish.
• Replace a section: plaster that is soaked, crumbling or detached over a large area is cut back and filled in with new material, sized to match the wall's thickness so the repair sits flush.

Matching the finish

Old plaster walls aren't perfectly flat, and many have a smooth hard finish or a slightly sandy texture. A patch that's dead flat on a wavy wall shows as much as a crack does, so we feather repairs to follow the wall, match the texture, prime and then paint. When touch-up paint won't blend, we paint the wall corner to corner; our patch and paint service covers both in one visit.

Where we repair plaster

Plaster is everywhere in our older neighborhoods. See local pages for plaster and drywall repair in Bethesda, Chevy Chase and Washington, DC, plus drywall repair across Montgomery County, including Kensington. Not sure what your walls are made of? Read how to tell plaster from drywall. For newer walls, see our main drywall repair page. Plaster is also the reason picture hanging in older homes needs the right anchors.