Mold behind drywall: what it is and what to do
Mold behind drywall grows where paper stays wet. Drywall is gypsum wrapped in paper. Wet paper feeds mold in days. You cannot see it from the room. You smell it. Or you find it when the wall opens.
How it starts
Leaks. Plumbing and roof leaks feed walls silently. By the time the stain shows, mold is established.
Floods. Basement water wicks up the board. The bottom two feet go first.
Chronic damp. Unvented baths. Condensation on cold walls. Slow and steady.
What we do when we find it
Small, contained mold in the board: we cut it out with margin. We check the framing. We let it dry. We rebuild with damp-rated board. Large or widespread mold: we stop. You need a remediation specialist. Then we rebuild after they clear it.
We are drywallers, not remediators. We tell you which call fits.
Prevention
Fix leaks fast. Vent your baths. Use damp-rated board below grade. Keep gutters and grading moving water away. Mold needs wet paper. Take away the wet.
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