Three questions decide it
- What kind of water? Clean supply water, Category 1, gives drywall a chance. Category 3 water like sewage or outside floodwater means the soaked drywall comes out.
- How long was it wet? EPA says dry within 24 to 48 hours. Drywall that stayed wet past that may already be growing mold on the back side.
- What shape is it in? Sagging, crumbling, bubbling paper or a soft feel means it is done.
What the meter says
Drywall can be damaged at just over 1 percent moisture content on a gypsum scale meter. That is why a wall that feels dry can still be in trouble. A tech takes readings around the wet spot to find its edges, then compares to a dry wall in the same house.
Water climbs drywall from a wet floor. That is called wicking. A leak in one spot can leave a line of wet drywall a foot or more up the wall.
Drying in place
When the water was clean and caught early, drywall can often be dried in place. Base is pulled, small holes are drilled behind where it sat, and dry air is pushed into the cavity. The holes are hidden when the base goes back on.
The flood cut
When drywall has to go, it is cut in a straight line above the highest wet reading. That is a flood cut. It opens the cavity so the studs and bottom plate can dry, gets rid of wet insulation, and leaves a clean edge for the patch. Cutting by eye at the water stain often leaves wet drywall behind.
Mold behind the wall
Signs include a musty smell, stains that spread, and paint that bubbles. If you can see mold, EPA says testing is usually not needed. If you can only smell it, opening a small inspection hole where readings are highest is often more useful than a lab test. Mold over about 10 square feet is a job for pros per EPA.
Do not clean mold with these
- Bleach mixed with ammonia, ever.
- Bleach stronger than CDC's limit of 1 cup per gallon of water.
- Paint over mold. It comes through.
EPA's advice for hard surfaces is detergent and water. Porous drywall with mold in it is removed, not scrubbed.