Key facts: Wet drywall: save or replace
- Drywall dried within a day or two of a clean-water leak has the best chance of staying, in line with the EPA's mold guidance [1].
- The EPA notes that porous materials such as ceiling tiles that become moldy may need to be thrown away [1].
- The EPA says paint applied over mold tends to peel and recommends cleaning and drying surfaces first [1].
- Federal lead-safe rules apply to many renovation jobs that disturb paint in homes built before 1978 [2].
How drywall reacts
What water does to a sheet of drywall
Drywall is a gypsum core sandwiched between paper facings. Gypsum soaks up water and softens; the paper soaks it up too and, if it stays wet, is a good food source for mold. Drywall also wicks water upward, so the wet line inside the wall is often higher than the stain you can see.
Briefly wet drywall that dries quickly often recovers its strength and can stay. Drywall that was soaked for a long time, sagged, crumbled or grew mold usually cannot. The decision is about the water, the time and the condition of the board.
Decision guide
Save or replace: the main factors
| Situation | Usually | Why |
|---|---|---|
| Clean water, wet briefly, dried within a day or two | Save | Gypsum and paper recover if dried quickly |
| Clean water, wet for several days | Often replace lower section | Higher mold risk and weakened board |
| Grey water | Case by case | Depends on time and how far it wicked |
| Sewage or outdoor floodwater | Replace | Contaminated porous material cannot be reliably cleaned |
| Ceiling drywall sagging | Replace | Weakened by weight of water; can fall |
| Soft, crumbling or swollen board | Replace | Structural strength lost |
| Visible mold growth | Replace affected area | Mold is hard to remove from porous paper and gypsum |
| Wet insulation behind it | Remove to dry | Batts trap moisture against the gypsum |
Drying in place
How drywall is dried without removing it
When drywall looks like it can stay, the baseboard is usually removed and small holes are drilled near the bottom of the wall, behind where the baseboard sits. Air from air movers or a wall cavity drying system is directed into those holes so the inside of the wall dries along with the face. Dehumidifiers keep the room air dry so the moisture has somewhere to go.
Readings are taken on the drywall and, where possible, the framing behind it. When they match an unaffected wall, the baseboard goes back on and covers the holes. See structural drying.
Flood cuts
When and how drywall is cut out
When drywall has to go, contractors often make a straight horizontal cut a little above the highest wet reading, sometimes called a flood cut. Cutting a straight line makes the repair easier: a new strip of drywall goes in below and the seam is taped and finished.
Cutting also exposes the insulation, which usually comes out if wet, and lets the studs and bottom plate dry properly. In a finished basement or a wall that took on a lot of water, it is often the fastest route to a dry wall.
In older homes, check before cutting. Houses built before 1978 may have lead paint, and some older wall and ceiling textures may contain asbestos. [2] Testing first avoids spreading hazardous dust.
Warning signs
Signs your drywall needs to come out
- It sags, bulges or feels soft when you press it.
- The paper is peeling, bubbling or delaminating from the gypsum.
- It crumbles at the bottom edge or around fasteners.
- There are dark spots or fuzzy growth on it.
- There is a musty smell from the wall that does not go away.
- The water that soaked it came from a sewer, toilet backup or outside floodwater.
Ceilings
Wet ceiling drywall is a special case
Water on top of a ceiling, from a leak above, adds weight to drywall held up only by screws. A ceiling that sags is holding water and can come down. Keep people out from under it and turn off any light fixtures in it.
Ceiling drywall that sagged usually comes out. Ceilings that only got damp can sometimes be dried in place. Insulation above a wet ceiling almost always has to be removed. See burst pipe water damage.
Do not
Mistakes to avoid with wet walls
Do not paint over water stains on a wall that is still wet. The EPA notes that paint over mold tends to peel, and paint over damp drywall traps moisture. Stain-blocking primer belongs on a wall that is confirmed dry.
Do not push furniture back against a damp wall, and do not reinstall baseboards until readings say the wall is dry. And do not assume a wall is fine because it feels dry on the surface.
Oregon homes
Plaster walls and older Oregon houses
Many older homes in Portland, Salem, Eugene and the Rogue Valley have plaster and lath walls rather than drywall. Plaster behaves differently. It is denser, holds water longer and can lose its bond to the wood lath behind it if it stays wet. It does not feed mold the way drywall paper does, but the lath and framing behind it can.
Plaster that is still firmly attached and dries out can often stay. Plaster that sags, bulges or has come loose from the lath usually needs repair. Drying plaster takes longer than drying drywall, so expect the contractor to run equipment for more days and to take readings carefully before calling it done.
Cabinets
Drywall behind kitchen and bathroom cabinets
Water under a sink often runs behind and beneath the cabinets, wetting drywall that nobody can see. Cabinet bases made of particleboard swell easily. Contractors often remove the toe-kick or the cabinet floor to dry the space, and sometimes pull the cabinet to reach wet drywall behind it. Checking there with a meter is the only way to know.
Swollen particleboard does not shrink back, so a cabinet base that has puffed up usually needs replacing even after the drywall behind it is dried.
Questions
Wet drywall questions
Can drywall be saved after it gets wet?
Often, if it was wet with clean water, dried within a day or two and has not sagged, crumbled or grown mold. Contaminated water means replacement.
How high should wet drywall be cut?
Usually a little above the highest wet reading, since water wicks above the visible stain. Contractors measure before cutting.
Do I need to replace the insulation behind wet drywall?
Usually, if it got soaked. Wet insulation holds water against the framing and dries poorly in place.
Can I just paint over a water stain?
Only once the wall is confirmed dry and free of mold, using a stain-blocking primer.
My house is old. Is cutting drywall safe?
Test first. Pre-1978 homes may have lead paint, and some older textures may contain asbestos.