Mold prevention after water damage comes down to moisture

Mold spores are already in ordinary indoor air, so nobody can remove them all. What decides whether they grow is moisture. That makes fast water extraction and thorough structural drying the real prevention work.

After drying, a simple hygrometer tells you whether the room is staying within EPA's suggested range. Run bath and kitchen fans, and use a dehumidifier in damp basements.

EPA suggests small areas can often be handled by a homeowner with hard-surface cleaning and protection, while bigger or hidden growth deserves a professional. Porous materials such as ceiling tile and carpet may need to go. Rules for mold work differ by state, so ask about licensing where you live.

Musty smell with no visible growth may point to a wet cavity. Moisture readings can help locate it. See wet drywall: save or replace.

Check behind baseboards, under vinyl flooring, inside cabinet bases, around window frames and on the back of drywall. Carpet pad and insulation hold water for a long time. Closets on outside walls stay cool, so condensation can build up there even after a room seems dry.

Attics and crawlspaces deserve a look after any roof leak or plumbing failure, since nobody spends time there.

People with asthma, allergies or weakened immune systems can react more strongly to mold, and they should stay away from cleanup work. If anyone has symptoms that worry you, talk to a doctor. Wear gloves, eye protection and an N95 respirator for small cleanup jobs, as EPA recommends for this sort of work.

Prevention fits when materials are wet but no growth has started, and the work is mainly drying and humidity control. Remediation applies when growth is established, especially over a large area or in an air system. Many states have their own rules for mold work, so ask what applies where you live.

A musty smell with nothing visible often means a hidden wet spot. Find that before anything else.

See how to find hidden moisture and can carpet be saved after a flood?.

EPA treats about 10 square feet, a patch a little over three feet on each side, as a rough dividing line. Below it, a homeowner can generally handle cleanup with EPA's guidance. Above it, the agency points people toward more extensive remediation guidance and, often, experienced help.

Size is not the only factor, though. Bring in help no matter how small the patch looks if the moisture came from sewage or other contaminated water, if the growth may be in your heating and cooling system, or if someone in the home has a health concern. Growth you can see may also be only the visible edge of a larger problem inside a wall.

CDC says hard surfaces can be cleaned with soap and water or household cleaners. If you do use bleach, CDC's limit is no more than 1 cup of laundry bleach per gallon of water, with windows open and with rubber boots, gloves and goggles on. Never mix bleach with ammonia or other cleaners, since dangerous fumes can result. EPA, for its part, does not recommend biocides such as bleach as a routine practice in mold cleanup.

Do not paint or caulk over a moldy surface, as EPA warns. The coating is likely to peel, and it leaves the source behind. Dry the area completely once it has been cleaned. And the most important step is the one people skip: fix the moisture source, or the growth will return.

EPA cautions that disturbing a hidden colony can release large numbers of spores. If you suspect growth on the back of wallpaper, inside a wall or under a subfloor, slow down and think about containment before pulling anything off. An experienced contractor can isolate the work area with plastic sheeting and filter the air.

Also, take care if the home is older, since opening a wall can disturb lead paint or asbestos. Ask how those materials will be handled before work starts. Water and power lines also run in those cavities, so a saw or pry bar can make a bad day worse.

CDC does not recommend routine testing, because there are no established standards for what level of mold is acceptable. You do not need to know the species in order to deal with it, as CDC notes that any mold you see or smell should be removed, along with the source of the moisture.

Sampling can sometimes help in specific situations, such as when a doctor asks for it or when you need to locate a problem that nobody can find. If you do test, ask what question the result will answer before you pay for it. A single air sample with no comparison outdoors or in another room says little. Moisture readings are often the more useful step, since they point directly to what can be changed.

CDC lists stuffy nose, wheezing and red or itchy eyes or skin among common reactions in sensitive people, while some people have no effects at all. Those with asthma or mold allergy can react more severely. Immune-compromised people and people with chronic lung disease may develop lung infections. Talk with a doctor about any symptoms that worry you, and mention the water event.

Ready.gov goes further for anyone with a breathing condition or low immunity, advising them to keep out of a building that has active leaks or mold they can see or smell. Temporary arrangements for them are a reasonable part of the plan, even if the rest of the household stays home.

EPA advises making sure a contractor has experience with mold cleanup and checking references. Ask whether they follow EPA's guide to remediation in schools and commercial buildings, or guidelines from ACGIH or IICRC. If they plan to spray something and leave, ask how the moisture source and the existing growth are going to be addressed.

It is also fair to ask who will decide when the job is done, and how. Some people prefer to have one firm assess and a different firm carry out the work, and certain states have requirements on this. Water Damage First is a referral service, so whoever you reach through (833) 610-0241 is independent, and these questions are ones you can put to them directly.

A vacation home or a house waiting to be sold can quietly grow mold after a small leak, because no one is there to notice a smell or to run the air conditioning. Keep humidity in check with a dehumidifier set to drain on its own, or with air conditioning set to run periodically in humid climates. A connected humidity sensor lets you check the reading from afar. Shut off the water main when you leave, if the house has no fire sprinkler that depends on it, and ask someone to walk through after any storm.

Rental property calls for clear rules. Ask tenants to report leaks promptly, and respond quickly when they do. A small report dealt with early rarely turns into the kind of problem described on this page.

In the humid South, outside air often carries more moisture than indoor air, so opening windows can make a wet room worse. Air conditioning and dehumidifiers do the heavy lifting there. In cold northern climates, the concern is condensation on cold surfaces, and warm moist air getting into attics or wall cavities. Dry mountain regions offer more help from the outside air, although basements can stay damp there too.

A hygrometer takes the guesswork out of it. Compare the number inside with what you get from outdoors, and only ventilate when the outside air is actually drier. No single rule fits every house, so go by the readings.

Where you live changes mold prevention after water damage. See Oregon, Connecticut, Delaware, Kansas, Louisiana, New Hampshire, Chicago, Dallas, Colorado Springs, Cedar Hill, Lake Stevens, Norcross, Port Charlotte, Prosper, Atlanta, Indianapolis.

Go straight to the first steps: emergency mold services.