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I live close to the water and there is a high water table around my house. Therefore a lot of water vapor passes through the basement walls. I would like to be able to store stuff in my basement and ideally finish it and not have to worry about mold.

There are a range of options I have been looking at. Such as sealing the basement walls and floor with water blocking adhesive compound such as Drylok, Thoroseal, Blue Max liquid rubber and Xypex Hi-Dry. I am not sure which product would provide the best seal and longest life span in my situation?

I currently have a small dehumidifier in my basement that runs constantly. I don't want to get a bigger unit as this small one is already a big hog on my utility bill. I was thinking of getting an air exchanger that would bring in Fresh air as well as remove humidity and be less costly to run then a dehumidifier. Does anyone have any experience using these to remove humidity from a basement? I found this company EZ Breathe but it looks like they are only installed by professionals.

Putting up a vapor barrier such as 6mm polysheathing on over the concrete worries me a little. I would imagine the water would condense on the sheathing and build up between it and the foundation. I also hear that you are supposed to put the vapor barrier infront of any insulation but that doesn't make sense to me since you are going to have the water building up behind the vapor barrier.

Putting in French Drains inside or outside is a little to expensive for me right now so that isn't an option.

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3 Answers 3

I wanted to comment but I don't have the rep so: I live in Germany where it rains a lot. Our house is built on clay. The basement used to be really damp - it would run down the walls. So here is what I did:

  1. Dry it from the outside - dig down the outside of the wall, a trench about 60 cm wide, let it dry, paint with bitumen and fill the gap with pebbles so it can dry all the time. I did this in sections, over several years, when I felt like it, good exercise. This thing did more good than any others.

  2. Keep moist air out. Make sure the any doors and windows are relatively airtight and don't open them if outside is warmer than inside. This sounds counter-intuitive, but the warm air carries water, comes in and deposits it on your cool walls. You can air in summer in the night, if it gets cooler than inside. Otherwise wait for autumn!

  3. Heat the dampest room and leave its door open so moisture will get out and upstairs. I do this in one cellar room with a little fan heater on a timer, 30 min a day. Much cheaper than running the dehumidifier.

  4. If you have a utility room for drying stuff, seal it off from the rest with a good door. Have a little window partly open. never hang up washing in the other rooms.

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You probably won't like this, but there's only one way to permanently deal with such situations: you have to stop the water before it hits the concrete.

I've done this several times with different houses. It isn't so expensive if you do the labour. And the labour need not be onerous -- take the evening time you'd spend on the computer or TV, and instead, dig a few feet closer to the footing. You'll end up with a bone-dry basement, and you'll be in better shape, too!

First, dig down to about 6" below the footing. This can and should be done in sections, of perhaps 10' or so. Once you get a section dug out, let the outer wall dry, with the aid of a heater, if necessary. Then on a very hot day, slather black tarry sealer on the wall, and while the tar is hot and sticky, cover it with 6 mil plastic. On the next section, overlap the plastic by a foot or so, being sure to tar the first plastic with the next wall section before covering. Repeat in sections until done.

It might take a year and cost $200 in materials. Got kids? Make their allowance contingent on so much digging!

Or bite the bullet and hire someone to do it for you. But it's the only way to really get it dry.

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digging 6' down the the footing is no easy task, but if one does that, I'd suggest taking the additional step and install a proper drainage tile system, insulate the outside, and install a drainage plane (dimpleboard). –  DA01 May 16 '12 at 18:17

If it's ground water, the issue isn't water vapor, but rather just plain water. Is the water table close or higher than your basement slab? If so, not a whole lot you can do to completely stop moisture issues, as that basement was just built in a bad spot.

That said, the main solution would be a sump pump and drainage tile system. Any water coming up through the earth dumps into the drainage tile, into the pump well, and gets pumped out. Again, though, if the water table is already higher than the basement slab, that'll be a never ending battle as well.

That said, perhaps the issue isn't as much about ground water as you think. Does it get humid in your region? If so, then 'damp' basements are par for the course. Basement walls are usually always going to be cooler than the air, and, a such, will be were condensation forms in a humid environment.

To prevent that, you need to a) dehumidify and/or b) insulate the walls.

A dehumidifier constantly running tends to be a normal part of any basement in a humid zone, so that's a good start. Insulating with walls with XPS or EPS foam will help too, it'll keep the moist air further away from the cold wall.

I can't say if an air exchanger would help or not. If it's including an A/C system, it could help (as the A/C is a dehumidifier) but otherwise I have a hunch you'd just be pumping more humid air into the space.

Products like drylock don't do a whole lot. They're not strong enough to prevent hydrostatic water pressure (high water table) and do nothing to prevent condensation. They're a bit of a gimmick.

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