Symptoms
- Dark spots, patches, or fuzzy growth on drywall or paint
- Musty smell near the affected wall
- Sometimes paired with peeling paint or a soft wall surface
Likely causes
- CommonCondensation from a cold wall meeting humid indoor airExterior walls, especially poorly insulated ones, can get cold enough to condense moisture from the room.
- CommonHigh indoor humidity generallyHomes without enough ventilation or with humidity above 60% support mold growth on many surfaces.
- PossibleHidden leak inside the wall from plumbing or the roofA slow leak can keep the back of the drywall wet even when the front looks only lightly affected.
What to do
- Press on the affected drywall; if it's soft or crumbly, there's likely ongoing moisture behind it, not just surface condensation.
- Check nearby plumbing, exterior walls, and the roof above for a possible leak source feeding the area.
- For a small area of surface mold on solid drywall, clean with a mold-specific cleaner or diluted bleach solution and dry the area thoroughly.
- Improve airflow and reduce humidity with fans, exhaust vents, or a dehumidifier, especially near cold exterior walls.
- Cut out and replace drywall that's soft, crumbling, or covers a mold area larger than a couple of square feet.
- Fix any leak found before repainting or patching, since mold will return otherwise.
- Consider a mold-resistant paint after the area is clean and dry as an extra precaution.
Tools and parts
- Gloves
- Mask
- Scrub brush
Mold cleanerSearch: “mold and mildew cleaner”
Replacement drywallSearch: “drywall sheet”
When to call a pro
Call a mold remediation specialist for areas larger than about 10 square feet or if you have respiratory sensitivities.
Safety
Use caution
Wear gloves and a mask when cleaning mold, and avoid disturbing larger moldy areas without protection since it can release spores into the air.