Understanding the Risk
Mold isn't automatically dangerous, but it's never something to take casually. Most household molds cause respiratory irritation and allergic reactions. Some people are more sensitive than others. And certain mold species, including some that grow on water-damaged drywall, produce mycotoxins that can cause more serious health effects.
You can't identify dangerous mold by looking at it. Black mold isn't necessarily toxic. Greenish mold isn't necessarily safe. The color and appearance don't tell you what species you're dealing with.
What matters more is the extent. Small amounts of surface mold are manageable. Large amounts, hidden mold, or mold on people with respiratory conditions are situations where professional assessment makes sense.
My family has no particular mold sensitivities, so I handled the bathroom ceiling myself. But when my asthmatic niece visits, I take mold a lot more seriously. Context matters.
Assessing What You Have
Before deciding on approach, figure out the scope of the problem.
Surface mold only: You can see mold on the painted surface but the drywall behind it is dry and intact. This is common in bathrooms and other humid areas. Usually DIY fixable.
Mold with water damage: The drywall is or was wet, and mold has grown on or into the damaged material. Might be DIY if small. Might need professional help if large.
Hidden mold: You smell musty odors or see water staining, but the mold itself isn't visible. It's growing behind the drywall or in wall cavities. This almost always needs professional assessment because you don't know what you're dealing with.
The EPA guideline is that areas under 10 square feet can be DIY remediated. Over that, or if there's HVAC involvement or if anyone has respiratory health issues, professional remediation is recommended.
Why Bleach Doesn't Work
This was news to me. Bleach is the classic mold killer, right? Wrong, at least on porous surfaces like drywall.
Bleach is mostly water. On non-porous surfaces like tile or glass, the chlorine kills surface mold effectively. But on drywall, the water penetrates into the porous material while the chlorine stays on the surface. You're essentially feeding water to the mold roots while only killing the visible surface growth.
Worse, the mold that survives can come back more aggressively because you've eliminated competing organisms that were keeping it somewhat in check.
Proper mold cleaners use different chemistry. Concrobium and similar products create an environment that prevents mold growth without the bleach problems. For actual killing, fungicides designed for porous surfaces work better.
I know people who've used bleach on drywall mold for years and swear by it. They're probably just re-bleaching the same spot over and over, mistaking the color removal for actual remediation.
DIY Surface Mold Removal
For small areas of surface mold where the drywall is dry and sound:
Preparation
Wear an N95 respirator mask and rubber gloves. Not negotiable. Disturbing mold releases spores, and you don't want to breathe them or get them on your skin.
Open windows for ventilation. Turn off any HVAC systems that might spread spores through the house. Some people cover nearby surfaces with plastic, but for small areas I don't bother.
Cleaning
Spray the moldy area with your chosen mold cleaner. Let it sit for the recommended time, usually 10-15 minutes. Wipe with disposable rags, don't just spread it around. Bag the rags immediately.
If mold remains after one pass, repeat. Some stubborn mold needs multiple treatments. If it's not coming off, the mold has penetrated the surface and you're looking at drywall replacement rather than cleaning.
After Cleaning
Once the mold is gone, treat the area with a mold-preventive product or apply mold-resistant primer before repainting. Regular primer and paint will just give the mold something new to grow on.
Address whatever caused the mold in the first place. Clean the bathroom exhaust fan. Fix the leak. Improve ventilation. The mold will return if the conditions that caused it continue.
When the Drywall Has to Go
If mold has grown into the drywall, not just on the surface, cleaning won't fix it. The affected drywall needs to be removed.
Signs that mold has penetrated: The drywall is soft or crumbly where the mold is. The mold keeps returning after cleaning. You can see or smell mold but the surface looks clean. There's visible mold on both sides of the drywall.
Removing mold-contaminated drywall is messier than regular drywall work. You need containment to prevent spreading spores. Full protective gear including respirator, goggles, and disposable coveralls for anything significant. The removed material goes in sealed bags directly to outdoor disposal.
For anything over a few square feet, I'd recommend professional remediation. They have proper containment setups, air filtration equipment, and experience doing this safely. The cost is typically $500-1500 for moderate bathroom-sized areas. More for major problems.
My friend's basement after a flood was a professional job. The water had been sitting for days before he discovered it. Mold throughout. The remediation company sealed off the basement, set up negative air pressure, removed all the affected drywall, treated the framing, and then it was ready for rebuild. Total cost was around $6,000. He couldn't have done that safely or effectively himself.
Prevention
Way easier than remediation.
Control humidity. Bathrooms need working exhaust fans run for 15-20 minutes after showers. Kitchens need range hoods. Dehumidifiers in basement spaces. Target below 60% relative humidity, ideally below 50%.
Fix leaks immediately. Every day a leak continues is more mold growth potential. That slow drip under the sink that you've been meaning to fix? Fix it today.
Ventilate. Air movement prevents the stagnant humid conditions mold loves. Even just opening windows periodically in problem areas helps.
Use mold-resistant materials in wet areas. Mold-resistant drywall in bathrooms. Mold-resistant paint. These aren't mold-proof, but they slow growth significantly.
After my bathroom ceiling adventure, I cleaned the exhaust fan, verified it was actually venting outside, and set a reminder to clean it annually. Also switched to mold-resistant paint for the ceiling. Two years later, no mold return.