Originally Posted by AndreasMergner
Ok, these are all good points. I agree with both of you, Matt and Floyd. Here's my synopsis, but I'm looking for discussion so please give me your thoughts!
Plastic sheet: Seals well. Water from slab will not evaporate. Mold will grow. Does not prevent condensation on top of plastic because it is not a thermal barrier.
drycore/Delta-FL: seals well, except for the edges. Water will evaporate around the 1/4" edges. Mold won't grow.
EPS/foam: seals well, but is semi-breathable. Mold won't grow. Prevents condensation due to thermal barrier.
Andreas' problems with above:
- Gallons per day can come from the slab. 1/4" gap around drycore/delta and semi-breathable foam will not let this water evaporate. Relative humidity will be greater than 50%, so mold can grow.
- drycore/delta has no thermal barrier. Hot humid air can go around the edges and condense on the cold concrete. This will increase humidity within the space between the floor and drycore/delta in warmer months.
Andreas' positive notes:
- Floors don't tend to be a problem since there isn't fiberglass or wood involved (unlike walls). Floors tend to be a problems when flooding occurs, which is a different issue entirely.
- Some people do not even have a problem with carpet directly on the slab, which is likely the riskiest method in regards to mold.
- drycore/delta allows pooling water to go somewhere. This water can run downhill hopefully to the sump pump. If walls are framed directly on the ground, the only way for the water to go to the sump is through the doorway (assuming no threshhold). If walls are built on top of drycore/delta, sound isolation becomes an issue (also see Logan's thread why this may be bad). Plastic film does not allow this pooled water run off.
Now, every situation is different. I seem to have "wicking" or capillary action of water coming through the slab at cracks. I have no standing water, just dampness at those spots. I would like to FastPlug those cracks and then go over the floor with Drylok. I have a new French drain that seems to work well after rains. If I can just stop the wicking, I shouldn't have any water coming in. The play foam tiles are made of EVA foam which is a vapor and thermal barrier. There are seams between the tiles that could make is "semipermeable". EVA foam doesn't support mold and won't be ruined by flooding.
Originally Posted by AirBenji
Argh there is so much to consider and there are quite a few options! I am struggling with this as well! I was planning on simple carpet and pad over slab, but you guys are scaring me...might have to rethink that one...keep us posted on what you decide, AM. I'd like to stop by this weekend and see your progress!
It has been suggested in many sources to first test to see what moisture is actually coming through your slab. One way is to tape down a piece of plastic and let sit for a day or two and see what the moisture/condensation level is in the sealed portion. If the builder installed a vapor barrier between the underside of slab and gravel, the moisture penetration may be minimal, although those barriers are normally not too reliable due to tears that occur during construction etc. Of course, that test is not gospel as conditions will vary depending on season, conditions in the house etc.
I think you have a pretty good synopsis Andreas. Dricore counts on some airflow around the edges of the flooring and suggest keeping your baseboard up a bit to help with that. To further increase that air movement, you can cut some register openings as well. They have a pretty good FAQ on their site if you haven't seen it.
Regarding the thermal barrier comment on Dricore/Delta, if there is none (I agree it is minimal), then the slab temp should be more closely equalized to the room temp (something less than room temp, but warmer than if the flooring was a thermal barrier) which would therefore be less prone to condensation due to temp diff, correct?
I really haven't looked into the matts you linked to so don't have an opinion on that approach. Here are a couple links that should provide you many hours reading
if you haven't already found them:http://www.eere.energy.gov/buildings...s/db/35017.pdf
(see fig. 15 as example of XPS construction technique)http://index.nrc-cnrc.gc.ca/cgi-bin/...nrc-cnrc.gc.ca
I seem to recall another topic that may (or may not) be interesting. In a typical basement you'll have a foot or two above grade, with the remainder below grade. The portion above grade and below grade (to the level of your frost line) present the biggest opportunity for condensation in a finished wall system, due to effect of frost line and outer ground soil temp. As you go lower into your basement the temperature goes up since it's below the frost line.