The Musty Smell After a Water Leak Won't Go Away: What It Means

Weeks Later and It Still Smells

The plumber fixed the line a month ago. The stain on the ceiling dried. You've opened windows, run the fan and burned through two candles a week, and the hallway still smells like a damp basement every morning.

Fixing a leak stops new water. It doesn't dry what already got wet. A smell that hangs on for weeks usually means something is still damp out of sight, or that mold got started before it dried. The EPA's brief guide to mold, moisture and your home says: "You may suspect hidden mold if a building smells moldy, but you cannot see the source, or if you know there has been water damage and residents are reporting health problems."

The job is the same in every case: find the moisture, deal with it, and fix the source. The EPA puts that last part plainly: "If you clean up the mold, but don't fix the water problem, then, most likely, the mold problem will come back."

Five Places to Look

The EPA lists where hidden mold tends to sit: "the back side of dry wall, wallpaper, or paneling, the top side of ceiling tiles, the underside of carpets and pads, etc.", plus "areas inside walls around pipes (with leaking or condensing pipes), the surface of walls behind furniture (where condensation forms), inside ductwork, and in roof materials above ceiling tiles". In a house after a leak, that turns into five places to check, nearest the water first.

1. Behind the baseboard nearest the leak. Water spreads along the floor first. Smell and feel along the bottom of the wall, and look for staining or paint that has bubbled.
2. Under the carpet pad. Lift a corner of the carpet near where the water was and touch the pad. It can look fine from above and still be damp underneath.
3. Under hard flooring at the edge of the leak. Vinyl, laminate and tile can hide a wet subfloor. Check the edges, the transitions and around cabinets and the toilet base.
4. Inside the wall. If the leak was a supply line, ice maker line or drain inside a wall, the cavity behind the drywall is the likely source. Our guide to wet drywall smell covers the checks before anyone cuts.
5. The heating and air system. If the smell is in every room, or is stronger when the system runs, look near the returns and the air handler. The EPA names ductwork as a place hidden mold can sit.

Sweep the Room With a Meter

A moisture meter from a hardware store turns a guessing game into a map. You don't need to know what a "good" number is. You need a comparison.

1. Get a dry reference. Take a reading on the same material, drywall to drywall or floor to floor, in a room that never got wet.
2. Work out from the leak. Start at the baseboard nearest where the water was and take readings in a grid, along the wall and up it.
3. Write it down. A rough sketch of the room with the numbers on it is enough.
4. Repeat in a few days. Readings that stay well above your dry reference, or that don't move, show you where the problem is.

Stop there. Don't start pulling drywall or wallpaper to look. The EPA says investigating hidden mold "will require caution when the investigation involves disturbing potential sites of mold growth", warns that "removal of wallpaper can lead to a massive release of spores if there is mold growing on the underside of the paper", and adds: "If you believe that you may have a hidden mold problem, consider hiring an experienced professional."

What a Dry-Out Can Miss

If the smell is back after a job was called finished, ask what was checked. These are the questions worth asking whoever did the drying, or yourself if you did it:

• Did the carpet pad get pulled and dried, or only the carpet?
• Was the subfloor under the flooring checked, or only the surface?
• Did anyone check inside the wall, including any insulation?
• Were readings taken at the end and compared with a dry area?
• Is the water source itself fixed?

The EPA's mold course covers the floor in two lines. For carpet: "To dry carpet and backing within 48 hours, remove water with a wet vacuum, pull the carpet and pad off the floor and dry them using a fan to blow air over them." For what's under it: "If the under-flooring is wet, it should be dried using a vacuum or by exposing it to the air."

The same course says: "In most cases, mold will not grow if wet or damp items are dried within 24-48 hours." Weeks later, that window has passed, which is why a lasting smell is worth taking seriously. And the CDC lists what mold can grow on: "paper, cardboard, ceiling tiles, and wood", as well as "dust, paints, wallpaper, insulation, drywall, carpet, fabric, and upholstery."

Bleach, Sprays and Ozone

Bleach. The EPA says: "The use of a chemical or biocide that kills organisms such as mold (chlorine bleach, for example) is not recommended as a routine practice during mold cleanup." It also says: "Dead mold may still cause allergic reactions in some people, so it is not enough to simply kill the mold, it must also be removed." The CDC's bleach guidance, "no more than 1 cup of household laundry bleach in 1 gallon of water", is for hard surfaces. And the EPA warns: "Never mix chlorine bleach solution with other cleaning solutions or detergents that contain ammonia because toxic fumes could be produced."

Sprays and candles. They change what the room smells like for a while. They don't dry the pad, the subfloor or the wall, so the smell comes back.

Ozone generators sold as air cleaners. The EPA's page on ozone generators sold as air cleaners says that "at concentrations that do not exceed public health standards, ozone is not effective at removing many odor-causing chemicals", and that at those levels it "does not effectively remove viruses, bacteria, mold, or other biological pollutants."

When to Call Someone

Reasonable points to stop doing it yourself:

• The smell has outlasted a proper dry-out and you can't find the source.
• Your meter readings near the leak stay well above your dry reference.
• The leak was inside a wall, or under hard flooring you can't lift.
• You can see mold over more than a small patch. The EPA says that if the moldy area is less than about 10 square feet, in most cases you can handle the job yourself.
• Anyone in the house has symptoms.

On that last one, the CDC says: "Exposure to damp and moldy environments may cause a variety of health effects, or none at all." It adds: "People with asthma or who are allergic to mold may have severe reactions." The EPA's guide says: "For more detailed information consult a health professional."

You don't need a lab to name the mold first. The CDC says "CDC does not recommend mold testing" and that "You do not need to know the type of mold." Mr. Fresh offers mold remediation, and our guide to mold inspection vs mold remediation explains which of the two you need. For a step-by-step on clearing the smell once the source is found, see how to get rid of a musty smell after water damage.

Smell Won't Go Away? Find the Moisture First.

Mr. Fresh Carpet Care is a family-owned carpet cleaning and water damage restoration business in Fairfield, in business since 2013, with IICRC-certified technicians. On a water job we document the damage with photos and moisture readings and work with your adjuster. A smell that keeps coming back after the source is dry is a job for odor removal.

Call or text (707) 816-7103 and describe the smell and where the leak was. If something is still wet, emergency water extraction runs with 24/7 dispatch across Fairfield, Vacaville, Suisun City and Benicia. More on our services at mrfreshcarpetcare.com.

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