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I’ve got a basement dying to be remodeled and thus brings up the age old question of what to do about moisture migration through the slab. Ideally I’d rip out the old slab, put down a vapor barrier, rigid insulation and a new slab; the works. Of course I’d really love to not have to do that. I’ve done a bit of reading and have come across a possibility I wanted to get feed back on. What was suggested was to cut back the concrete in a 2′ wide perimeter, dig down a few inches, install vapor barrier, insulation and new concrete just in this area. The idea being less moisture in the middle of the slab and most of the heat lose at the perimeter. Does this sound realistic or are the “facts” all wrong?
Thanks!!!
Jared
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Dear Jared,
Nope, don't fall for that. Consider two distinct sources of moisture.
1. Foundation leakage. Your perimeter measure may address that.
2. Slab diffusion. Since all of the soil under the slab is saturated, moisture will slowly but constantly work through the concrete. You may never see it b/c the surface evaporates too fast. But it can amount to gallons a day.
Happily, a nice slip of diffusion barrier such as Tu-Tuf will stop that for pennies a foot. Then build on top.
Regards, Fred
*Putting a plastic over the slab like Tu-Tuf wouldn't be the smartest thing to do. The concrete will sweat underneath and become rancid.Use a trowelled on or sprayed on moisture or water proofing that can be applied from the inside.
*Jared,Both of these guys make sense, to some degree. But, before you do any "fixes", determine if you really have a problem. The soil under your slab might be saturated, though it might not. It depends on a lot of conditions, including the nature of the soil, the location of the water table and site drainage. Do you have noticeable moisture in there now? Does it change with the seasons? A small amount of vapor diffusion could easily be accommodated by your ventilation system. Moving air, in a controlled manner, is almost always a better way to control moisture than "barriers". Though I did say almost.By the way, how far under ground is the slab? The only significant heat loss through the ground in in the first 3 feet.
*Tim,You seem like a nice fellow but don't try to complicate a simple question. The poster is looking for answers not questions. He sounds like he has some experience, not a new DIY, so treat him accordingly.
*Previously, people have posted here with good reasons to go with a tile floor in the basement: - the ceramic tile will breathe and allow water vapor to move thru the floor into the room's air (preventing the mold farm concern if you put a non-permeable layer on the floor) - the above fact could allow you to skip additional moisture mitigation like trying to put drain tile and or moisture barrier under your slab as you described in your question, if your moisture level is 'normal' (meaning, that you don't have ground water rising, and you have effective down spouts and gutters on the roof to keep water well away from your foundation, and so on). Making that decision will depend on your house's conditions. - finally, you'll probably want to use a dehumidifier down there in the summer months just to keep the humidity below ~70%.If you are quite set on having carpeting, tile anyway, and use throw rugs and let most of the floor breathe.The challenge with doing spot testing (like putting a sheet of poly on your slab for 48 hours and checking for moisture formation) is that some moisture issues are seasonal and not every year provides the same amount of moisture (rain fall, water table, cleanliness of the gutters from one year to the next, and so on). But being aware of these factors should help you to decide the best course of action in your particular situation.hope this helps.
*LFred,I was trying to simplify the issue. He wants to remodel. Jared didn't say moisture migration through the is a problem, unless I misunderstood what he posted, just what someone had suggested to him. Before everyone gets busy solving a problem, its a good idea to establish that there IS a problem. Everyone is assuming, I was asking.
*Tim,Of course you're right about testing for moisture.The only question asked by the poster was about the suggestion given him to cut the slab back and to address only the perimeter. He wanted to know if that would work and the answer is that it would be a waste of money.I think we all agree on that point.Then it becomes an issue of what to do, instead of what is proposed.
*I've only used this company's product on sidewalls, but i was completely pleased with it there. Maybe someone has some stories to tell about installing it over slabs?http://www.thewrap.net/product/dfl.html
*Dear Kerr,I have never seen ceramic tile breathe. But lets say that it could. Where would you suppose all the water goes, once it's in the room air?Roof rot repair specialist, Fred
*SG,Plastic is still plastic. This stuff is still part of the sucker market. You have to appreciate the fact that it doesn't allow air to flow because there is no where for the air to go and no way to exchange the moisture/mold from underneath.Instead of simply producing links for people to blindly follow, you should think out the logic first.
*Apparently this stuff is commandeering an increasingly large part of the "sucker market"--i keep seeing it oftener and oftener in magazines like JLC and FHB. Logic:Dorken talks about the air going to the walls and up. If this is so--and i found no evidence to the contrary in my googling--no more water vapor would be entering the house than enters at present; it would just be detouring around the Pergo. If the vapor doesn't come out on its own with its hands up, perhaps it can be coaxed out with a dehumidifier or one of those fancy HRV's about which i know almost nothing...yet. As stated, i'm also looking for links to info or anecdotal accounts of bad experiences with this product; do you have any?Besides that, Brent Anderson sent me the nicest monograph on bentonite and sold this stuff to me for my sidewalls, where it did a splendid job. Based on the fact i red'd good info from him before, and rec'd info from him on using this on a slab, i would be willing to look into it further and even advise others do so, too. Though not blindly, of course. But i believe this poster sounds like he has some experience, not a new DIY, so i'll treat him accordingly.
*Moisture in or on concrete will not harm it provided it is static. (Consider bridge piers and similar structural concrete underwater) The problem comes when the moisture migrates to the surface, taking the dissolved salts with it and leaving them as efflorescence. The effect of a sheet of plastic on the concrete is no different from that of an applied moisture barrier, although I would prefer the applied coating rather than having to thoroughly seal the joints in the plastic.
*Splinter,"oftener"Logic is not "Dorken talks about the air going to the walls and up. If this is so--and i found no evidence to the contrary in my googling"And "googling" is not thinking. Even Mr. Gilham understands a little about plastic layers over moisture so it's shouldn't be too hard for you either.Give logic one more try. I promise it won't hurt and you might learn something of value.With regards to your closing remarks, "Though not blindly, of course. But i believe this poster sounds like he has some experience, not a new DIY, so i'll treat him accordingly" It would be better for the poster IF you also had a little bit more experience BEFORE you gave out advice.
*Curiouser and curiouser...Gabe, this is an interesting game, but winning it isn't important enough to me to blow up this poster's thread. Come on over to the Tavern and we'll continue the third-generation theme, OK?Colleen
*Splinter,Gabe doesn't post here anymore. We know/work with him and there are 4 of us that post under this title. One is a concrete form specialist, another is an insulation contractor, one other is a carpentry contractor and the last is a technician at a research facility. None of us participate in any games.
*Gabe, you need some "advice". It's your signature to put "advise" where a noun needs to go.Sorry to hear about the multiple personalities.
*You've got to love it when the Dick Tracey's of the world think they've solved another great train robbery. Welcome to Canadian terminology, eh.What a joke. Keep quessing.
*Splinter,Excuse me for butting in, but I just wanted to say from a lurker's standpoint, that I appreciate your demeanor and method of posting. I find value in the issues and points you bring to the discussion. It certainly is a breath of fresh air as opposed to some of the other posts (from a number of people) that are thinly veiled self esteem issues. Thanks.
*I'm whelmed.