Technician in a respirator inspecting pipes inside an opened wall cavity. Example of the work involved; the photo does not show a specific property or a job for this site.
How plaster reacts to water
Traditional plaster is applied in layers over strips of wood lath, with some plaster pushed through the gaps to form keys that hold the wall in place. When water from a burst line soaks it, the plaster itself often survives, because it does not turn to mush the way the gypsum core and paper facing of drywall can. The weak points are the keys and the lath. Wet wood lath swells, and when it dries it can shrink and loosen, letting sections of plaster pull away.
Ceilings are the bigger concern. A plaster ceiling that has lost its keys can drop in heavy slabs. Signs include sagging, a hollow sound when tapped gently, and cracks that widen or form a rough circle. Walls usually fail less dramatically but can bulge or crumble along the base where water collected.
Plaster also dries slowly. It is dense, and in older homes it may be covered with layers of paint, including oil-based coats, that slow evaporation. Moisture readings matter more than how dry the surface feels.
Plaster and drywall after the same leak
Plaster over lath
- Hard surface often stays intact when wet
- Lath can swell, then loosen keys as it dries
- Ceilings can fail in large, heavy pieces
- Dries slowly; may need longer equipment time
- Patching often needs a plaster-experienced trade
Gypsum drywall
- Softens and sags when saturated
- Paper facing can grow mold if left wet
- Cut-outs and replacement are routine
- Dries faster when cavities are opened
- Standard materials and finishes
Before deciding to keep or remove wet plaster
General information for Denver, not a quote or professional advice. In an emergency, call 911.