Get tips on waterproofing a dirt floor basement. Find out how to keep moisture out of your dirt floor basement and install a concrete slab.
LESLIE: Mike in New Hampshire is dealing with a moist situation in the basement . Tell us about what’s going on.
MIKE: We have a typical New England home whereas it has large, granite walk-through walls and a dirt basement. If we go away during the summertime – that is anywhere, really, between April and October – and we leave the house closed-up, it’s very damp-smelling when we come back. We tried a dehumidifier . The dehumidifier costs like $60 a month; the thing runs continuously. I heard about a tangential fan, which is contractor installed. But all these things are really costly. I was wondering, is there any cure for a dirt basement floor by some other means of ventilation?
TOM: Well, there are a number of things. Is there any possibility that you may want to actually pour a floor down there?
MIKE: Yeah, we’d actually thought about it. In fact, I was thinking of leveling it and then using gravel as a base and see how that affected the condensation.
TOM: (overlapping voices) Gravel won’t necessarily help but if you put plastic sheeting down and poured a slab over it – even if it’s a very thin slab, what we call a dust cover, that actually will make a big difference because what you’re having here is evaporation of the moisture off of the soil.
TOM: The other thing to do is to make sure you pay attention to your drainage conditions outside because if you have good, positive outside drainage conditions, Leslie, I think that will reduce the volume of humidity and moisture inside the house.
LESLIE: Yeah, Mike. You want to look at the grading around your foundation perimeter. You want to make sure that all of the soil slopes away from the house and you want to go down about six inches over four feet so you do get all of that moisture just moving away from the house itself. And you want to look at your gutter system  and your downspouts.
LESLIE: You want to make sure that everything is free-flowing and any downspouts that you do have, you want to make sure that there isn’t just sort of, you know, that small return and it deposits all that water against the foundation wall. You want to try to move those downspouts at least four feet away from the house; you know, get it as far away from that foundation wall as you can.
MIKE: (overlapping voices) Oh, yeah. Good idea.
LESLIE: Whatever you can do to move that moisture away is going to keep that moisture out of your basement.
MIKE: Yeah, Leslie, I think you hit the target there because there are some gradations there that go backwards; in other words, not away from the house …
TOM: (overlapping voices) Yeah, exactly.
LESLIE: (overlapping voices) Mm-hmm, go towards it.
MIKE: … but towards the house.
TOM: Mm-hmm. Yeah. Very, very common condition, Mike, and that’s the solution.
MIKE: Great. Well, thanks, buddy. I appreciate that.
TOM: You’re welcome. Thanks so much for calling us at 888-MONEY-PIT.