Mold control in a dry basement?
October 3, 2011 6:34 AM   Subscribe

Mold control in a dry basement?

I have a very dry unfinished basement in a new house. Not a drop of water anywhere. A couple of years ago, shortly after we moved in, we found a whitish mold growing on some older wooden furniture and certain cloth items.

We had someone come check it out and they pretty much laughed at us. He said it was the driest, most perfect basement he'd ever seen. He advised us to run a dehumidifier and that seemed to have stopped the mold growth. I figured there was some moisture down there from the concrete curing and put it out of my mind.

However, recently I've noticed it growing again. A table, a pair of boots, etc. White splotchy, dust-like mold.

Everything I google about mold seems to be for damp, old basements. Advice about sealing cracks and getting rid of water. There's nothing about controlling it in a dry basement.

So what do I do? I can continue to run the dehumidifier but that doesn't seem to prevent it from growing. It's a somewhat tight house, would some sort of air circulation help? Is there a "mold bomb" I can run that would kill it once and for all?

It's a whitish mold, not the deadly black stuff, but we all suffer from allergies and we'd like to stop it. We have a lot of stuff stored down there that I don't want ruined. I’d also like to finish part of the basement some day but I don’t want to do that until we get this under control.

We're in New England, so humidity down there is a given, but the dehumidifier should take care of that. The dehumidifier drains to a sink, so it runs pretty much all the time.

posted by bondcliff to Home & Garden (4 answers total) 2 users marked this as a favorite
I live in MA, have lost belongings in the past to the mold you describe, and just had a plumber out to work on my dehumidifier's auto-drain setup this morning.

Do you know how moist the air in your basement is? My dehumidifier gives a readout of the humidity level. Even when the floor and walls are dry, the number can still get pretty high. Depending on the size of your basement, one dehumidifier might not be enough to maintain a low enough moisture level to keep the mold at bay, even when it's running continuously.
posted by cranberry_nut at 7:00 AM on October 3, 2011

I'm in a similarly new, tight, dry house as yours and I've seen the same thing, especially in the walled-off workshop part of the basement that doesn't benefit from the drying effect of the furnace (which runs even in summer to heat domestic water). The suggestion I have seen elsewhere, which I have not tried but which makes sense, is to install an exhaust fan that pulls air from the basement to the outdoors in such a way that air from your upstairs living space is pulled down into the basement. Pulling outdoor air directly into the basement tends to cause mold, as walls, floors and stuff that's in the basement are all cooler than the outside air (in summer, when I think most of the problem occurs). But reversing the flow pulls warmer air down, warming up at least the stuff in the basement and preventing mold growth.

Google "basement exhaust fan" to find products, including reversible fans. I think this is the one I first heard about. These fans will use much less power than the dehumidifier. I think some of them have humidistats so they only run when necessary. The recommendations sometimes include scooping the exhausted air from near the floor where the heaviest, moistest air would be. As a side benefit, if you have any radon infiltration, the fan is pulling that out, too. The ultimate solution may be both an exhaust fan and a dehumidifier that runs during very humid weather.

I've also caulked a quarter-inch gap between the concrete floor and the concrete walls all the way around the foundation — in my case to help stop radon infiltration, but presumably it also stops moisture. And I've put a plastic cap over the floor drain that leads to a drywell — cap is light enough to float away in case of flooding but heavy enough to stop most of the air flow.

The other thing, of course, is simply to avoid storing stuff that's a likely substrate for mold down there, like furniture, cloth, cardboard etc.
posted by beagle at 7:16 AM on October 3, 2011

I think the biggest thing contributing this sort of mildew is the temperature differential in the summer. Anytime you open a door, a blast of warm, humid air comes into the basement and it hits the cold surfaces and condenses. I find that it's mostly objects resting on the floor that turn mildewy. The most final way to deal with it is to insulate the walls with spray-foam and put a layer of pink foam insulation on the floor with a layer of plywood over it. In the meantime, we found that an air cleaner helps.
posted by bonobothegreat at 7:22 AM on October 3, 2011 [1 favorite]

"It's a somewhat tight house, would some sort of air circulation help?"

If you are getting less than half an air change per hour then you need to provide mechanical ventilation. The correct way to do this is with a Heat Recovery Ventilator or HRV. Even houses that aren't that tight can benefit from an HRV; especially if there are stagnant areas with lower air flow.
posted by Mitheral at 7:28 AM on October 3, 2011

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