Wet drywall: when it can stay and when it has to go

Drywall that got wet with clean water, was caught quickly, has not softened or crumbled, and has no soaked insulation behind it can often be dried in place. Drywall soaked by sewage or floodwater, drywall that has been wet for several days, drywall that has gone soft or swollen, and drywall with wet insulation behind it is usually cut out.

Drywall is a gypsum core faced with paper on both sides ^[1]. The gypsum can tolerate getting wet and drying again; the paper is what makes wet drywall a mold concern, because it is food for mold when it stays damp ^[2]. That is why time and water type matter so much in the decision.

Drywall pulls water upward by capillary action, often well above the visible waterline. Contractors use moisture meters to find where the wet area actually ends, which may be a foot or more above the stain. That reading sets how high any cut needs to go.

When removal is needed, contractors usually cut a straight line at a consistent height, often somewhere between 2 and 4 feet, above the highest wet reading. A straight cut makes the repair simpler: a strip of new drywall goes in, gets taped and painted, and the wall looks whole again.

Exterior walls and some interior walls have insulation in the cavity. When fiberglass or cellulose insulation gets soaked, it holds water against the back of the drywall and the framing, and it dries very slowly. Wet insulation also loses its insulating value. That is why walls with soaked insulation are usually opened: the insulation comes out, the cavity dries, and new insulation goes in before the wall is closed.

Interior walls without insulation are much easier to dry in place, because air can move through the empty cavity.

Ceilings are a special case because gravity works against them. Wet ceiling drywall loses strength and can sag and fall, especially with insulation or water sitting on top of it. A ceiling that is stained but firm and flat can sometimes be dried once the insulation above is dealt with. A ceiling that is sagging, soft or holding water is drained carefully and removed in the wet area. Never stand under a sagging ceiling. See burst pipe water damage for the common scenario.

Many older houses in Wilmington, New Castle and Newark have plaster on lath instead of drywall. Plaster is denser, holds more water and dries more slowly, but it tolerates getting wet better than drywall and is often worth drying in place. Before cutting old walls, consider lead paint and possible asbestos; EPA's lead-safe rules apply to paid work disturbing paint in homes built before 1978 ^[5].

Not all wall board is the same. Bathrooms and basements sometimes have moisture-resistant drywall, often with a colored face, which resists water better but still has paper facing and can still grow mold if it stays wet. Tile walls may be over cement board, which tolerates water well, or over ordinary drywall, which does not. Basement walls may be wood paneling over furring strips, which traps water against the foundation.

Each of these changes how a wall dries. Tiled walls and paneling block evaporation, so contractors often dry them from the other side or remove them. Ask the contractor what your walls are made of before deciding.