Plaster at a glance

Typical era
Common in Denver houses built before roughly the 1950s, when drywall became standard.
Construction
Two or three coats of lime or gypsum plaster pressed onto wood strips or metal mesh, with plaster squeezed through the gaps to form keys that hold it on.
Water tolerance
The plaster itself does not dissolve like drywall paper and gypsum, but wet wood lath swells and keys can break.
Drying speed
Slow. Thick plaster holds moisture and releases it gradually.
Hidden concern
Older paint layers and some old plaster textures may contain lead or asbestos.

What actually fails

When water soaks a plaster ceiling, the danger is rarely the plaster melting away. It is the bond. Wood lath swells as it absorbs water and shrinks as it dries, and that movement can snap the plaster keys that hold the ceiling up. A ceiling that looked fine during the leak can start to sag or crack weeks later as it dries.

Paint often bubbles or peels on wet plaster, and older lime plaster can leave white mineral deposits, called efflorescence, on the surface as it dries. Those are cosmetic. Cracks that widen, a ceiling that sounds hollow when tapped gently, or any visible droop are structural warning signs.

Because plaster holds moisture deep in its body, a quick surface reading can be misleading. Restorers usually use a meter that reads deeper into the material and compare it with a dry wall in the same house. Drying can take noticeably longer than drywall, and removing baseboards or drilling small vent holes is sometimes used to let air reach the cavity behind.

Drying in place versus removal

Often dryable in place

  • Clean water from a supply line or radiator
  • Plaster still firmly attached, with no sag
  • Damage limited to staining, bubbling paint or fine cracks
  • Lath accessible for drying through baseboard or small openings

Often removed

  • Sewage or other contaminated water
  • Ceiling sagging, bulging or separating from the lath
  • Plaster crumbling or soft to the touch
  • Persistent moisture and odor after a reasonable drying period

Before anyone cuts into old plaster

  1. Clear the room below a wet ceiling

    Keep people out from under any ceiling that is bulging, cracked or dripping.

  2. Ask about testing

    Ask whether paint should be tested for lead and textured plaster for asbestos before demolition. Colorado requires state-certified asbestos professionals for regulated work; the Colorado Department of Public Health and Environment has details.

  3. Map the moisture

    Have wet areas mapped on walls and ceilings, compared with a dry reference elsewhere in the house.

  4. Choose a repair approach

    Small areas can often be patched with plaster or a plaster-compatible system. Large areas may be replaced with drywall, which changes the look and feel of a historic room.

General information for Cherry Creek, not a quote or professional advice. In an emergency, call 911.