Mold in basements: causes, cleanup and when to call a pro

Where it grows

Usually behind things. Behind drywall, on the paper facing of insulation, on boxes sitting against the foundation walls, in carpet and carpet pad, behind furniture, on baseboards and around the rim joists. I’ve also seen a lot of mold around areas that got wet at one point and never fully dried out.

Is it mold?

Color won’t tell you if a mold is “toxic.” I’ve seen black, green, gray and white mold. I wouldn’t identify a type of mold by looking at a picture, and I wouldn’t say black mold is worse than green. Efflorescence is not mold. It’s usually white with a mineral look, powdery or crystalline, and it shows up on masonry when water has carried salts to the surface. Mold is a living organism. Sometimes you can’t tell just by looking at it, so you have to look at what it’s growing on and where the moisture is coming from.

Can I clean this mold myself?

Can I clean this mold myself?

Answer all five. Your answers aren’t saved or sent.

1. Is the moldy area larger than about 10 sq ft (roughly 3 ft by 3 ft)?

Yes No

2. Did the water come from sewage or other contaminated water?

Yes No

3. Do you think the mold is in your heating or cooling system or ducts?

Yes No

4. Does anyone in the home have health concerns about mold?

Yes No

5. Is the water or moisture problem still there?

Yes No

This checklist follows EPA guidance. It doesn’t test for mold or replace an inspection; see mold inspection and testing.

Basement mold removal: how to clean it safely

If you have a small area that can be cleaned and the water source has been corrected, you can do this yourself. Wear gloves, eye protection and at least an N95 respirator if you’ll be disturbing moldy material. I don’t want you brushing dry mold all over the room. I like to clean hard surfaces with detergent and water, remove what can’t be cleaned, and make sure everything dries out completely. Bleach is not a magic solution. I would never tell someone to spray it and they’re done. Even if you kill the mold, you still need to clean it off, because some people can react to dead mold too. Vinegar isn’t something I use as a general solution in my work. There are commercial products that have their place, but none of them replaces cleaning, drying and controlling the moisture.

What has to go and what can stay

I usually remove porous materials with significant mold growth: drywall, carpet pad, insulation, ceiling tiles and some engineered wood products. Concrete, masonry, metal and other hard surfaces can usually be cleaned. Solid lumber can often stay if it’s structurally sound and the growth is only on the surface. If the wood is already rotting, that’s a different issue.

When not to do it yourself

• More than about 10 square feet of growth
• Contamination from sewage
• Dirty floodwater
• A lot of affected drywall or insulation
• Possible mold inside the heating or cooling system
• Significant hidden contamination
• Several rooms involved
• Someone in the home with serious breathing problems or a weakened immune system
• You’d have to open a wall without knowing what’s behind it

Professional remediation usually includes containment, removing what can’t be cleaned, HEPA cleaning and drying, once the moisture problem has been corrected. The mold in crawl spaces guide walks through those steps. For prices, see mold remediation cost. To decide whether testing is worth it, see mold inspection and testing.

Myths

• “Spray it and the mold is dead.” Killing mold isn’t enough. The EPA says dead mold can still cause allergic reactions and has to be removed.
• “Bleach is the answer.” The EPA doesn’t recommend biocides such as bleach as a routine part of mold cleanup, and bleach must never be mixed with cleaners that contain ammonia.
• “Black mold is the toxic one.” Color doesn’t tell you how a mold will affect someone.
• “A test kit will tell me if I have a problem.” See mold inspection and testing.
• “An ozone machine will take care of it.” See basement smells.

Health

Everyone reacts to mold differently. The CDC says some people get a stuffy nose, sore throat, coughing or wheezing, burning eyes or a skin rash, and people with weakened immune systems or chronic lung disease can develop lung infections. If someone in your home has health concerns, talk to a doctor before you start cleaning.

Keeping it from coming back

• Keep humidity below 60%, ideally 30–50% (basement humidity)
• Fix leaks and outside drainage first (basement water)
• Dry anything that gets wet within 24 to 48 hours
• Keep boxes and furniture off the foundation walls
• Don’t paint or caulk over mold