Mold after water damage: what you can do yourself, and when to stop

Fix the moisture first, or nothing else matters

Every line of EPA's mold guidance starts from the same fact: mold needs water, and it will come back as long as the water does. Its homeowner guide says to fix leaks and other water problems as soon as possible and to dry water-damaged areas and items within 24 to 48 hours to prevent mold growth. Cleaning growth off a wall that is still wet, or that gets wet again next time it rains, is a chore you will repeat every few weeks until the drywall is gone.

So the order is fixed. Stop the source: the valve, the appliance, the roof, the grading. Dry the materials that can be dried, with air movers and a dehumidifier and a moisture meter to prove it, which is the subject of our 72-hour drying guide and the fans-and-dehumidifier schedule. Only then deal with whatever grew. If you found the leak late and growth is already there, drying and removal happen together, but the drying still has to finish; a remediated wall that stays damp is a remediated wall for about a month.

The timeline below is the one restoration crews work to. The 24-to-48-hour window is EPA's; the 72-hour mark is where restoration practice starts treating a wet material as a mold question as well as a drying question.

The 10 square foot rule, and what it does not say

EPA's homeowner guide, A Brief Guide to Mold, Moisture and Your Home, says that if the moldy area is less than about 10 square feet, roughly a 3 ft by 3 ft patch, in most cases you can handle the job yourself. Above that, or where there has been a lot of water damage, it points to its longer document, Mold Remediation in Schools and Commercial Buildings, which is the reference contractors use and which escalates containment and protective equipment through small (under 10 sq ft), medium (10 to 100 sq ft) and large (over 100 sq ft) jobs.

The same homeowner guide adds four conditions that move a job out of the DIY column no matter how small it looks. If the water was sewage or otherwise contaminated, call a professional who has experience with buildings damaged by contaminated water. If you know or suspect the HVAC system is contaminated, do not run it, and have it inspected before you do. If you have health concerns, consult a health professional before starting the cleanup. And if you suspect hidden mold, behind wallpaper or paneling, on the back of drywall, under carpet and pad, EPA's advice is to consider hiring an experienced professional, because opening those areas releases spores.

What the rule does not say is that 10 square feet of visible growth means 10 square feet of mold. Growth on the face of drywall is usually the last place it appeared; the back of the board, the paper against the studs and the insulation behind it have been growing longer. Ten square feet on the front of a wall is often a hundred behind it, which is why the question below the size question is always: what is behind this, and how long has it been wet?

The industry standard a remediation contractor works to is IICRC S520, the Standard for Professional Mold Remediation. Its vocabulary is useful even for a homeowner: Condition 1 is a normal indoor environment, Condition 2 is a surface with settled spores but no growth, and Condition 3 is actual growth. The point of remediation is to return Condition 3 and Condition 2 areas to Condition 1 by removing the growth, not by killing it in place.

Clean it or throw it out, by material

EPA's instruction for hard surfaces is to scrub the mold off with detergent and water and dry completely. For absorbent or porous materials, its wording is that they may have to be thrown away if they become moldy, and in restoration practice that "may" becomes "do" for anything that was wet long enough to grow. The table sorts the common materials.

What not to do

• Bleach as the cleanup. It is not a routine mold cleanup method in EPA's guidance, it does not penetrate porous material, it adds water to drywall and wood, and it does not remove anything. Detergent, scrubbing and removal do the work. Never mix bleach with ammonia or other cleaners.
• Painting, caulking or sealing over it. EPA's guide says not to; the growth continues underneath and the moisture is trapped where the meter cannot see it. Encapsulant coatings have a place at the end of a professional remediation on cleaned, dry wood, not as a substitute for removal.
• Ozone generators and foggers. EPA's guidance on ozone generators sold as air cleaners is that at concentrations within public health standards ozone does not effectively remove mold, that it would take 5 to 10 times those limits to do more than inhibit growth while the ozone is present, and that even then it may have no effect on growth embedded in porous material. Fogging a room with any product does not remove the drywall that is growing it.
• Running the HVAC through it. A return in the work room sends the dust everywhere, and a contaminated air handler or duct re-seeds every room it serves; EPA says not to run a system you suspect is contaminated.
• Dry-sanding or demolishing without containment. The cleanup turns a wall problem into a house problem.
• A shop vac without a HEPA filter. The exhaust is a spore sprayer.
• Leaving the pad, the batts or the back half of the drywall because the front looks clean. The front is the last thing that grows.

Signs it is bigger than it looks

Stop and reassess if any of these are true, because the job has left the 10 square foot column whether or not you can see it:

• A musty smell with little or no visible growth. The growth is inside a cavity, under a floor, or behind a finish. Smell is a better detector than your eyes for hidden mold.
• Growth on the back of a baseboard or a piece of trim you pulled. The wall behind it is wet lower and farther than the stain.
• The leak ran for a while. A supply line that dripped for a month, a roof that leaked all winter, a slow dishwasher leak. Time wet matters more than volume.
• It is on a ceiling or an exterior wall with insulation. The cavity above or behind is wet and cannot be dried from the room.
• Staining or dust at supply registers, or a smell when the system runs. EPA treats HVAC contamination as a professional job.
• More than one room, or growth that returned within weeks of a cleanup. Something is still wet or still leaking.
• Anyone in the house with asthma, allergies or a weakened immune system. EPA's guidance is to consult a health professional before starting; the practical version is that those people should not be in the house during the work, and the margin for a sloppy job is gone.

Does testing matter?

Less often than the people selling it suggest. EPA's homeowner guide says that in most cases, if visible mold growth is present, sampling is unnecessary, and it notes there are no federal limits for mold or mold spores to compare a result against. Testing earns its cost in a few situations: when you smell growth and cannot find it, where an inspector with a moisture meter, a borescope and air or surface samples can locate it; after a professional remediation on a large or contaminated-water job, where an independent assessor's post-remediation verification is how you know the containment can come down; and in landlord-tenant, real estate or insurance disputes where a third party's report is the evidence. A handful of states, Texas, Florida and New York among them, license mold assessors and remediators and require the company that assesses to be separate from the company that remediates; check your state before you hire either.

A home test kit that grows colonies in a dish tells you there are spores in the air, which is true of every house on earth. It does not tell you how much, where the growth is, or whether the wall needs to come out. A moisture meter answers more of those questions than a petri dish does.

When to stop, and what a proper remediation includes

Stop and call a remediation contractor when the growth is more than about 10 square feet or you suspect it extends into cavities you cannot see; when the water was sewage, floodwater or anything else contaminated; when the HVAC system or ductwork is involved; when someone in the home has a health condition that makes exposure a concern; when the growth came back after a cleanup; or when the loss is an insurance claim and the insurer wants a protocol and a clearance report. Many policies cap what they pay for mold, so the documentation of when the water happened and how fast it was dried matters more than usual; our claim checklist covers it.

A contractor working to IICRC S520 will: assess the moisture source and the extent of growth, with a meter and often a thermal camera; build containment with plastic and negative air machines exhausting through HEPA filters, so the work area is at lower pressure than the house; wear and dispose of the protective equipment above; remove and bag porous materials rather than treat them in place; HEPA vacuum, clean and where needed sand or abrade semi-porous surfaces; dry the structure to a documented dry standard; and have the work verified, on larger jobs by an independent assessor, before the containment comes down. Ask for each of those in the scope. If a quote is mostly fogging, spraying or a coating, with little demolition and no drying log, it is not a remediation.

When to call a pro

Call a restoration or remediation contractor for any of the stop conditions above, and call one first if the water is still coming in and you have not found the source; the drying has to start inside the first 48 hours and the mold question usually answers itself once the walls are open and metered. Call a plumber or a roofer for the source. Ask your physician, not a contractor, about health questions. The form below reaches vetted local restoration contractors through HelpMeNow.com; describe what you see, how long it has been wet, and where the water came from.