Controlling mold in a non-ventilated area (garage)

[viche]

I have a problem I thought some of you smart folks might know how to solve. I live in Maryland. I have a mostly above ground garage (cinderblock on one side and back, and drywall one the other side and ceiling.) There are two air conditioned stories above the garage (sort of looks like a townhouse garage). Anyway, twice now, toward the end of summer I have found mold on items stored in the garage (one rattan piece of furniture and some shoe laces). I do not park the cars in the garage and try to keep the doors closed to keep heat from accumulating and rising up into the living space. Vents run through an insulated bump down area in the ceiling of the garage. In the summer it gets very cool and damp in there. How do I get rid of mold conditions? Here are my thoughts on possible solutions:

1. I could try to keep the door open more, but it would affect cooling of the floors above when it gets to be 90 degrees in the garage. Also, I would think that while it would temporarily raise the temperature and thus lower the relative humidity, it would also let in more moist summer air and when the garage is closed at night and gets cold, the relative humidity would just rise higher.

2. I could put a portable humidifier in the garage. But it seems like it would be running all the time and waste a lot of energy.

3. Maybe I could install a UV light of some sort to discourage mold? I have some not-so-strong fluorescent lights in there now. Would leaving the fluorescents on 24/7 discourage mold? I don't know much about UV lamps.. Do they generate a lot of heat? Do they use a lot of energy? Are they expensive? Can you install one in a fluorescent fixture? Would they have any affect at a distance of 15 feet?

Any other thoughts or suggestions are appreciated.

Thanks!

[mbarson]

Mold needs three things to grow; a food source, correct temps, and moisture.
The only one we can control is the moisture. The source of your moisture is most likely from the ground entering through the block wall. I would start by sealing the concrete with a product like UGL Drylok. You may have to seal the floor also. Control roof run-off around foundation with gutters and proper grading. If high garage temps affect you indoor temps you need more insulation/air sealing between the garage and house. You could install a quality bath fan in the garage to promote air exchange but a dehumidifier will be needed if humidity levels can't be kept below 60% after sealing. Your lights will do nothing to discourage mold growth. Don't worry about UV. You are trying to treat the symptoms and not the cause of the mold. Control the moisture first.

[viche]

Thanks for getting me on the right track. Your suggestions make sense. Couple fo follow-up questions:

Do I really want to try to get outside air into the garage? I always thought that pulling in hot, moist summer air by leaving the garage door open or installing an exhaust fan would be a bad thing. Once the outside air cools in the garage, won't the relative humidity in the garage increase?

Secondly, what temps does mold need to form?

Thanks again.

[d_griff]

Thanks for getting me on the right track. Your suggestions make sense. Couple fo follow-up questions:

Do I really want to try to get outside air into the garage? I always thought that pulling in hot, moist summer air by leaving the garage door open or installing an exhaust fan would be a bad thing. Once the outside air cools in the garage, won't the relative humidity in the garage increase?

Secondly, what temps does mold need to form?

Thanks again.

You are correct in a sense that when you have your door open during the day in the heat, When you shut the door and the garage cools the moisture in the air will condense (Like a dew point) and it will be everywhere. I also agree with what was said below 100%. You need to stop the moisture from getting in first. I myself have this problem, My driveway is sloped toward my garage and house, there is a drain at the bottom but the pad is cracked and has settled, When it rains water finds its way under my garage door. I have two walls which are block and two are sheetrock, I have black mold growing on the bottom of the rock. MY next action is to replace the current sheetrock with greenboard, Paint it with a paint that can repel moisture and mold. and of course get the pad repaired and replaced to avoid the water from getting in, I have been in the house 6 months and plan on this after the other 20 things i have going on. It has been over 90 the past days in Philadelphia and my garage has to be in the 60's. It is real cool. Every time i open it i am adding to the problem.
I'm telling you this because as of now, The only option is to run a dehumidifier until you get the other issues resolved and as said below, Stop the moisture from getting in. But you never really will stop it because it is a cool spot that gets large rushes of outside air at times when you open it, Air moves form hot to cold, Every time the door is open in the summer you will let in a ton of moisture that will condense. And remember to empty the dehum. or you will cause more problems.

[Carnak]

What could be happening is the spaces above cool the garage off and the RH rises up towards 100% in there at night.

Dehumidier time

[Carnak]

put a bucket on the floor, go back a day later, pick up the bucket.

If there is a ring of moisture, its coming up through the floor.

I suspect air leaks in from the outside and you got about the same dewpoint as what is outside.

At night the garage cools off and your RH rises

[viche]

I'll try the bucket trick. Sealing and painting sounds like a plan too (after my 20 something list is caught up). It's sounding like even if I do that though, there will always be moisture in the garage...at least as high as outside, so some dehumidification will also be necessary.

What type of paint resists moisture and mold. I was thinking of just using a few coats of regular semigloss with a mold inhibitor like M1. Is there another product that would be more appropriate?