Plaster ceilings are common in houses that predate the widespread adoption of drywall, which occurred just after World War II. If paint is peeling from a plaster ceiling, it may be caused by saponification -- a chemical process whereby the plaster produces soap by reacting with alkyds in oil-based paints commonly used in the mid-20th century. In houses that date to the early 20th century, peeling paint can also be the result of an undercoat of calcimine paint, a chalk-like coating that eventually flakes off. Either way, repainting calls for specific preparation methods.
Scrape Off Peeling Paint
Your plaster ceiling may not have any peeling paint, and if that's true, you can paint over it just as if it's fresh drywall. If paint is peeling, though, it's important to remove as much of the flaking material as possible with a paint scraper or drywall knife. Any paint you don't remove may start peeling in the future, so prepare to spend time on this part of the project and be as thorough as possible.
- Cover the floor with a dropcloth and put on goggles.
- Mask the surrounding walls and all ceiling fixtures. You may prefer to disconnect fixtures that aren't too heavy, let them hang from the wires, and cover them with plastic bags.
- Turn off the power to all the ceiling fixtures.
- Use a ladder tall enough to allow you to work comfortably from the second-highest rung without overreaching.
Old ceilings may have one or more coatings of lead-based paint. Before scraping the ceiling, test a paint chip for lead. If the test is positive, wear a respirator when scraping; collect all the dried paint and dispose of it as hazardous waste.
Seal the Plaster
If, after scraping, you notice a waxy feel to the plaster, the previous paint probably underwent saponification. One way to counter this effect is to coat the plaster with an alkali-resistant sealer, which is usually an acrylic latex product. Another strategy is to skim-coat the ceiling with drywall joint compound, followed by a coat of PVA drywall primer. Skim-coating refers to the process of spreading a thin layer of joint compound with a drywall knife. Sand the joint compound after if dries and before priming.
Sealing Calcimine Paint
A chalky coating on the back of the the paint chips you scrape off may indicate an undercoat of calcimine paint, particularly if your house dates to the early 1900s. If so, scrub the ceiling with a solution of trisodium phosphate and water after scraping to loosen and remove the paint you can't scrape off; then seal the ceiling with a calcimine coating paint.
Repaint the Ceiling
Once you've taken care of peeling paint and sealed the plaster, you can repaint just as you would repaint a drywall ceiling. Use a latex wall or -- preferably -- ceiling paint.
- Cut in the edges of the ceiling with a synthetic-bristle brush.
- Roll the main part of the ceiling with a medium-nap roller. Use an extension pole so you don't have to work from a ladder.
- Apply at least two coats. Let the first coat dry overnight before applying the second.