Painting plaster walls in an older home: cracks, calcimine and what to fix first

Plaster walls take paint beautifully once they’re sound. The work is in the repairs: hairline cracks get mesh tape and setting-type compound, loose plaster gets reattached before patching, old calcimine and wallpaper paste get washed off or sealed, and every patch gets primed. Then a forgiving sheen keeps the wall’s old-house character without highlighting every wave.

Plaster is common in Grosse Pointe’s older homes and across much of Metro Detroit’s early-20th-century housing. It’s harder and denser than drywall, and worth keeping. Here’s how to get it ready for paint, and what to watch for along the way. For how we approach a whole project, see our interior painting page.

How is plaster different from drywall?

Drywall is factory-made gypsum panels screwed to the framing, with taped seams. Plaster was applied wet, usually in several coats, over strips of wood lath or, in many later homes, over metal lath or small gypsum panels called rock lath.

On wood lath, the first coat squeezed through the gaps between the strips and hardened into “keys” that lock the plaster to the wall. Those keys are what hold the wall together, and when they break, trouble starts.

Not sure which you have? Plaster sounds solid when you knock on it, resists a pushpin, and usually has gentle waves you can see in low light. Drywall sounds hollow between studs and takes a pin easily. Pulling a switch plate often shows the wall’s thickness, too.

Which plaster cracks are cosmetic, and which aren’t?

Most cracks in old plaster are hairline cracks: thin lines running from the corners of doors and windows, across ceilings, or along the joint where walls meet. Houses move as they settle and as temperature and humidity swing through the seasons, and rigid plaster cracks rather than flexes. These are cosmetic and very repairable.

Some cracks deserve a closer look before anyone patches them: cracks that are wide, that keep growing after repair, or where one side sits higher than the other, especially alongside doors that suddenly stick or floors that slope. Those point to movement in the structure, and a contractor or structural engineer should look at the cause. Paint won’t fix it.

What if the plaster is loose or sagging?

When enough keys break, a section of plaster lets go of the lath. You’ll see a bulge, a sag in a ceiling, or a crack with one raised edge. Tapped, it sounds hollow; pressed with a flat hand, it gives.

No crack filler will hold loose plaster, because the patch moves with it. The fix is to reattach it first: screws driven through thin perforated discs called plaster washers pull the plaster snug against the lath or framing, spaced around the loose area. Adhesive-injection systems made for plaster are another option. Once it’s secure, the washers and cracks are skimmed over and disappear.

Plaster that has crumbled, or is missing outright, gets cut back to sound edges and patched, either with new plaster or setting compound or with a piece of drywall shimmed to match the old wall’s thickness. A sagging ceiling shouldn’t wait; keep people out from under it until it’s secured.

How do you patch plaster so it lasts?

A smear of spackle over a plaster crack usually comes back. A lasting repair opens the crack slightly, cleans out loose bits, bridges it with fiberglass mesh tape, and fills it with setting-type compound, a powder mixed with water that hardens chemically. It shrinks less than premixed compound and sets up harder, closer to plaster itself. Old plaster is thirsty, so many painters brush on a bonding agent first so it doesn’t pull water out of the patch too fast.

Finish coats are feathered wide, often with an easier-sanding compound on top, so the repair blends into the wall instead of standing proud of it.

When a wall is a map of cracks and old patches, a skim coat makes more sense: one or two thin coats of compound troweled over the entire surface, then sanded smooth. It’s slow, skilled work, but it gives old plaster a uniform face again.

Every patch then needs primer. Compound is porous, and unprimed patches show through the finish as dull spots, which painters call flashing. Fresh plaster, as opposed to compound, is alkaline and needs time to dry and cure before painting; check the primer label for use over new plaster.

What is calcimine, and why does it make paint peel?

Calcimine, sometimes spelled kalsomine, is an old, inexpensive finish made from chalky whiting and glue mixed with water. It was widely used on ceilings in older homes, and it’s still up there in many of them, often under later coats of paint.

The problem is that calcimine is water-soluble and never truly hardens. Water in new latex paint softens it, and as the new film dries and tightens, it pulls the calcimine loose. The result is peeling in sheets or curls, often down to a chalky white layer, sometimes weeks after painting.

Before painting, calcimine has to be washed off with warm water and sponges, rinsing until the water runs clear, or sealed with a primer whose label specifically lists calcimine. Where it sits under old paint that’s already peeling, everything loose has to be scraped off first. Our ceiling painting guide covers the rest of the job.

What about wallpaper paste and old oil-based paint?

Many older walls have carried wallpaper at some point. Leftover paste is water-soluble too, and paint over it can crack, wrinkle or fail to stick. Wash the wall with warm water until it no longer feels slick or tacky when damp, then seal any stubborn residue with a primer made for the job, often an oil-based or shellac-based primer. Plaster generally handles the soaking of wallpaper removal better than drywall’s paper face, though gouges still need patching. Old paper that was painted over and is bubbling has to come off.

Old walls and especially old trim often carry oil-based paint. Latex brushed straight over glossy oil paint can peel, sometimes in strips. To check, rub a hidden spot with a cotton ball dampened with rubbing alcohol: if paint softens and comes off on the cotton, it’s latex; if nothing happens, it’s likely oil. Oil-painted surfaces get cleaned, dulled with sanding or a deglosser, and primed with a bonding primer before latex goes on. Our guide to what good prep looks like goes deeper.

Could there be lead paint on your plaster?

Homes built before 1978 may contain lead-based paint, and plaster repair disturbs old layers: drilling for washers, scraping loose paint and calcimine, sanding patches. The EPA’s Renovation, Repair and Painting (RRP) rule requires certified firms and lead-safe work practices for paid work that disturbs painted surfaces in pre-1978 homes, more than 6 square feet per room inside or more than 20 square feet outside. The EPA’s RRP program page has the details, and our guide to lead paint in older homes covers testing and what to ask.

Which sheen forgives old plaster walls?

Even well-repaired plaster has gentle undulations, and many owners of older homes like it that way. The goal is sound and clean, not drywall-flat. But sheen decides how much of that character shows.

Light skimming across a wall from a window or lamp catches every wave and patch edge, and glossier paints reflect it. Flat and matte finishes hide the most; eggshell is a common middle ground for living spaces, with a little more washability. Satin and semi-gloss belong on trim and doors, where their toughness pays off. Ceilings are usually flat. Deep colors also tend to show surface flaws more than light ones. Our paint sheen guide walks through each option, and our guide to painting older Grosse Pointe homes covers the rest of the house.

Prefer to have the repairs handled for you? Our wall and plaster repair service covers cracks, loose plaster, holes and skim coats — and the painting that follows.

Questions

Cracks, holes or loose plaster?See how Guiffre’s repairs walls and ceilings so the paint over them looks right.→