Mold grows where materials stay wet, usually behind walls, under flooring and in basements after a leak. This page explains how remediation works, what testing can and cannot tell you and what to ask any company that offers the work.
Do not disturb a patch of mold or spray it with bleach. Stop the moisture source if you can, and photograph the area. For health questions, talk to your physician, since this page does not give medical advice.
Musty smell and stains: what they usually mean
Homeowners search for a musty basement smell, black spots on drywall, dark staining on a ceiling, or fuzzy growth on stored items. Those symptoms point to long-term moisture. Mold itself is a result, and the source of water is the cause.
The EPA states that the key to mold control is moisture control. If water damage is dried within 24 to 48 hours, mold usually does not grow. If it is not, remediation may be needed. The best first step is finding and stopping the water.
What remediation actually involves
Remediation follows the ANSI/IICRC S520 standard for mold remediation. The work typically includes containing the area, using negative air so spores do not spread, removing contaminated porous materials such as drywall and insulation, cleaning surfaces and drying the structure.
Cleaning removes mold from surfaces that can be saved, such as framing. Porous materials with growth are removed. After the work, drying and a final check confirm the area is ready for rebuilding.
Found mold growth?
Do not disturb it. Call and ask about containment.
The remediation process
Each step prevents spreading and addresses the cause.
Contain
The area is sealed with plastic sheeting and negative air.
Remove and clean
Contaminated materials come out and surfaces are cleaned.
Verify and rebuild
The area is checked and then repaired.
Ask whether your state licenses mold work, and ask any company whether its crews work to S520.
Testing and what it tells you
Testing has a place, but it does not replace fixing moisture.
| Test | What it measures | Limit |
|---|---|---|
| Visual inspection | Visible growth and moisture | Cannot see inside walls |
| Moisture mapping | Where materials are wet | Does not identify mold |
| Air sampling | Spore counts in a sample | A snapshot, varies with conditions |
| Surface sampling | Presence on a surface | Does not measure exposure |
Testing questions are covered in more detail by an independent assessor, and results should always be read alongside moisture findings.
Questions to ask any mold company
Ask whether the crew works to ANSI/IICRC S520, how the area will be contained, whether they use negative air with HEPA filtration and how they will dispose of removed materials. Ask whether your state licenses mold work and whether the company holds the licence if one is required.
Ask how they will deal with the water source. A company that offers removal without a plan for moisture is selling a repeat visit. Get the scope in writing and read what is and is not included.
Mold after a flood or a long leak
Mold commonly follows a water loss that was not dried in time. If your home flooded, the order of work is cleanup of contaminated materials, drying and then checking for growth. The flood damage cleanup page describes the first steps.
If you find growth on materials that were wet for days, take photos and note where the water came from. That helps both the crew and your insurer, and it shows how long the moisture was present.
What affects the cost of mold remediation
Size and access matter most.
Area affected
A patch differs from a whole basement.
Materials
Drywall removal differs from cleaning framing.
Containment
Negative air and sheeting add setup.
Source repair
A plumber or roofer fixes the water.
Rebuild
New drywall and finishes follow.
Mold coverage varies. Policies often cover mold that follows a covered water loss, and exclude mold from long-term leaks. Check your policy and ask your insurer.
What to do first, and what not to do
These steps keep you from spreading growth or making the area harder to clean.
Safety steps
- Do not disturb or dry-brush visible growth
- Do not spray bleach or paint over it
- Stop the moisture source if it is safe to do so
- Ask a physician about any health concern
Common questions
Health questions belong with your physician. This site cannot give medical advice. What can be said is that mold needs moisture, and removing the moisture and the growth is the usual approach.
Small surface areas on non-porous material are sometimes cleaned by homeowners. Large areas or growth in walls call for a crew with containment.
Bleach does not address the moisture and does not penetrate porous materials. Removal and drying are the usual approach.
Not always. Visible growth and a moisture source usually tell you enough. If you want testing, use an independent assessor, not the company doing the removal.
If the moisture is fixed and materials are dry, growth usually stops. If the moisture returns, mold can too. No company can promise it will not return.
Standards and references
Ask any company whether its crews work to ANSI/IICRC S500, the water damage restoration standard, or S520 for mold. The EPA explains moisture control, and the Massachusetts Division of Insurance publishes insurance guidance.