Removal means finding the moisture and the affected material and taking them out of the equation, after which the smell goes and stays gone. Masking means putting something over the top: a fragrance, a fogged deodorizer, an ozone treatment. The smell comes back when the treatment fades, because the source never moved.
The distinction is easy to test. Ask what happens to the water. A quote for odor work with no answer to that question is a quote to cover the smell.
What a musty smell is
It is the by product of growth on damp material, and it is useful. A smell is a signal that something in the building is wet enough to support growth, and it usually arrives before anything is visible, because the growth is inside a cavity, under a floor covering or behind a finish.
That is why removing the smell first is backwards. The EPA states the general rule in one line: cleaning up the mold while leaving the water problem in place means the mold will most likely come back, and the smell comes back with it.
Where the smell is usually coming from
- A slow leak behind a vanity, under a dishwasher or at a supply line joint, wetting the back of a cabinet or the base of a stud bay.
- Ground water or run off entering a basement, where the material at floor level stays damp long after the puddle goes.
- Condensation on a cold surface, which is the version with no leak at all. The EPA advises keeping indoor humidity below 60 percent relative humidity, ideally between 30 and 50 percent.
- Carpet or a rug that got wet once and was dried by air, never to a measured standard, especially over a slab.
- The heating and cooling system, where a wet coil, a blocked condensate line or affected material near the return puts the smell into every room the system serves.
The last one explains the most confusing complaint in this trade, which is a smell that seems to come from everywhere. Air is being moved, so the source is not where the smell is strongest.
Why nothing is ozoned in an occupied home
Ozone is sold as an odor treatment and it does change the way a space smells. It is also a lung irritant, and using it in an occupied home means treating people in order to treat a smell. DHL does not ozone occupied homes, and a musty smell is treated as a symptom of moisture, so nothing is gained by overpowering it.
Where air and soft goods need treatment once the source is out, hydroxyl and HEPA filtration are used and textiles are deodorized, never perfumed. That order matters: the treatment comes after the removal, and it is the last step.
What removes the smell
- Find the moisture with meters, not by nose, including inside cavities and under floor coverings.
- Fix or arrange the fix for the water source, whether that is a plumber, a roofer, drainage outside or a dehumidifier running through the summer.
- Remove the affected porous material. Drywall, insulation, carpet pad and similar materials hold growth inside their structure rather than on the surface.
- HEPA vacuum and damp wipe what stays, over an area larger than the visible growth, because settled spores and fragments travel.
- Dry the assembly and read it at set points each day until it holds a dry standard.
- Treat air and textiles last, and only once the first five are done.
By the time step five is finished, the smell has usually gone on its own. Where it has not, something is still wet or something was missed, and the readings and the containment notes are where that gets settled.
The bleach question
The EPA does not recommend a chemical or biocide that kills organisms, chlorine bleach for example, as a routine practice during mold cleanup, and it warns never to mix a chlorine bleach solution with cleaners containing ammonia because toxic fumes can be produced. On a smell specifically, bleach adds a strong odor of its own for a few days, which people read as progress. It does nothing about the water inside the wall.
What you can do yourself
The EPA guide says that an area of less than about 10 square feet, roughly a 3 foot by 3 foot patch, can in most cases be handled by a homeowner. For a smell with no visible source, the useful homeowner steps are cheap: put a hygrometer in the room and read it over a week, run a dehumidifier if it reads above 60 percent, lift rugs off cool slabs, and check under and behind anything plumbed.
Call when the area is larger than that patch, when the smell is in or near the heating and cooling system, when the water was sewage or floodwater, or when the same spot has come back after being cleaned once.
When the smell follows a water loss
A smell appearing days or weeks after a leak usually means the drying stopped at the surface. The EPA advises drying water damaged areas and items within 24 to 48 hours to prevent mold growth, and a carpet that felt dry to a hand on day three was often still wet in the pad and the subfloor.
That is the everyday version of this problem in this service area, and it is why the water side and the mold side of the business are the same phone call. The drying method is on Water Damage Restoration and the remediation sequence, including written post remediation verification, is on Mold Remediation.
If a smell survives a completed job, ask for the moisture readings. A completed job has them, and they are the only way to settle the question either way.
This article is about Mold Remediation.