Eight Things I'd Never Spray on Mold, and What to Reach For Instead

By John Calhoun, owner of Mold Remediation Gettysburg PA · Updated October 26, 2026

Would you pay good money for a can that makes your basement smell clean while the mold behind the paneling keeps growing? Plenty of people do, because the shelf at the store is full of things that promise to kill mold and almost none of them mention the water. Here’s the short list of what not to spray, use or set off, with what the EPA and state and city health departments say about each one. The longer version of the answer is always the same: mold has to be removed and the moisture has to stop.

1. Bleach mixed with anything

Bleach plus ammonia makes chloramine gases. Bleach plus an acid, and vinegar counts, gives off chlorine gas. Both warnings come from Washington State’s health department, and New Jersey’s adds that bleach and rubbing alcohol form chloroform. The CDC’s instruction is simple: never mix bleach with ammonia or other cleaners. That includes spraying one product right after another on the same surface. If bleach is used at all, it’s for hard surfaces at no more than a cup per gallon of water. The full story is in does bleach kill mold.

2. Outdoor fungicides

This one surprises people. The EPA’s remediation guide for schools and commercial buildings says outright: don’t use fungicides developed for outdoor use for mold remediation indoors. A deck or lawn product is formulated and labeled for outside, and the EPA’s rule for any pesticide is that the label is the law.

3. Ozone

Ozone machines get sold as a cure for musty smells and mold. The EPA’s ozone generator page is blunt about it: kept within public health limits, ozone doesn’t do the job on mold. The agency says it would take five to ten times the allowed level to keep mold from coming back, and even then it may do nothing to mold embedded in porous material like ceiling tile or duct lining. For the health side, read the EPA’s ozone page itself.

4. Foggers and “dry fog” treatments

New York City’s health department guidelines say fogged or aerosolized biocides are not recommended for remediation, and Philadelphia’s guidance says the same. A fog lands on surfaces. It doesn’t scrub anything, and it doesn’t pull growth out of drywall paper or wood.

Total release foggers have a second problem. The EPA requires their labels to warn that a flammable ingredient may cause a fire or explosion if misused, and to tell you to turn off every ignition source, pilot lights included. In Gettysburg borough the Census Bureau estimates about 65% of homes heat with gas. A basement with a gas furnace or water heater is exactly where people want to set one off.

5. Paint, caulk and “mold-killing” primer over active growth

The EPA says not to paint or caulk moldy surfaces, and that paint applied over them is likely to peel. The EPA and CDC’s disaster cleanup guide puts it more simply: painting or caulking over mold won’t stop it from growing. New York City’s guidelines add that antimicrobial paints shouldn’t be used in place of removal and moisture control. Paint after the growth is gone and the surface is dry, not instead.

6. A fan pointed at the growth

Drying is good. Blowing air across visible mold is not. The EPA and CDC’s disaster guide says not to use fans if mold has already started to grow, because they may spread it, and the EPA’s commercial guide warns against moving spores into areas that weren’t affected. Clean or contain first, then dry. If you’re curious how professionals handle airflow on a real job, containment, negative air and HEPA scrubbers walks through it.

7. A garden hose or pressure washer on moldy material

No agency rule here; it’s practical. Blasting water at moldy wood or block throws loose growth around and soaks the material you’re trying to dry. For a hard surface, a wet rag with detergent does more good with less water.

8. More of the same spray

If the spot came back after the first treatment, a second can won’t change the outcome. Something is keeping that surface wet. That’s the point to stop spraying and start looking.

What to reach for instead

For a small area on a hard surface, the EPA’s recommendation is detergent and water, then drying completely, with an N-95 respirator, long gloves and goggles. Why plain soap works is in does dish soap kill mold. For porous materials that mold has grown into, the answer is removal, not chemistry. And if a quote leans heavily on fogging, ozone or an expensive spray, red flags in a mold remediation quote is worth a read.

This is John Calhoun at Mold Remediation Gettysburg PA. Before you spend money on a spray, I’ll find out where the water’s coming from. The list of mold services shows what I do instead of spraying, and the Gettysburg housing data page has the local numbers. More about me is on the mold remediation in Gettysburg, PA page.