Why it grows
Mold spores are in every home, and they need only moisture and something to eat, such as drywall paper, wood, dust or fabric. The Environmental Protection Agency advises keeping indoor humidity between 30 and 50 percent, and a hygrometer that measures it costs about ten dollars. Materials that are dried within 24 to 48 hours of getting wet usually do not grow mold. The common sources are a bathroom with no working fan, condensation on cold windows and outside walls, a slow leak under a sink and a damp basement.
Cleaning a small patch
The same agency draws the do-it-yourself line at about ten square feet, which is a patch three feet by three feet.
- Put on rubber gloves, goggles and an N95 respirator, and open a window.
- Scrub hard surfaces such as tile, glass, metal and sealed wood with detergent and water, and dry the area completely.
- Cut out and discard moldy porous material such as ceiling tile, carpet and crumbling drywall, because the growth runs through it and cannot be washed out.
- Seal the debris in a bag and launder your clothes.
Bleach is not needed for routine cleanup. It does not reach into porous surfaces, and it must never be mixed with ammonia or other cleaners. Do not paint or caulk over mold, since it keeps growing and the new finish peels. Blackened caulk around a tub has to be cut out, and the joint cleaned and dried for a day, before mildew-resistant silicone goes in.
Keeping a home dry
Run the bathroom fan during every shower and for twenty minutes afterward, and confirm that it actually vents outdoors. Pull furniture two inches away from outside walls so that air can move. In a basement, run a dehumidifier set to 45 or 50 percent. Outside, keep the gutters clear, and make sure downspouts discharge at least four feet from the foundation.
When it is beyond you
Call a remediation professional for growth larger than ten square feet, mold inside heating ducts, anything that follows a sewage backup or a flood, or a musty smell with no visible source, which often means growth inside a wall. Testing to identify the species is rarely worth the money, because the remedy is the same whatever the type. Anyone with asthma, allergies or a weakened immune system should leave the cleanup to somebody else.
Note Renters should report leaks and mold to the landlord in writing, with dated photographs. Repair duties vary by state, and the state attorney general's office publishes the rules for tenants.
