waterproofing basement walls

Old 03-06-02, 05:57 PM
Mr. Hometime
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Question waterproofing basement walls

I have a problem with moisture in the basement.
My house is a split level with 2 unfinished rooms downstairs.
The fiberglass installed by the builder now has mold in it.
I am going to tear it all out and replace it.
I've been told the problem is from my concrete walls "sweating".
How can I prevent this?
I have heard many different things.
-DryLoc paint
-Rigid foam (polysterene)
-6mil vapor barrier (both inside and outside stud frame

What I'm considering is the following:

dry-loc paint
1-2" rigid foam
fiber-glass (to fill in 2x4" frame)
6mil vapor barrier

Any suggestions??

Old 03-06-02, 10:31 PM
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You can go to http://www.eren.doe.gov/consumerinfo/refbriefs/bd4.html this is an U.S. Dept. of Energy brief on vapor retardents. It discusses Thermal-Moisture dynamic and the three ways moisture becomes a problem with insulation, namely air movement, diffusion through materials and heat transfer. It also discusses Relative Humidity and along with some of the other information implies Equilibrium Relative Humidity. This is probably where the source of the mold comes from. This is the ability of a material to absorb and expel (drying out process) moisture. Different materials do this at different rates. For an example, fiberglass has a low absorbancy and high expulsion rate. Whereas masonry has a much higher absorbancy and a slow expulsion rate with moisture. The two materials touch each other under certain conditions, the probability of condensation is high.

There is great debate over this subject and it seems most of us don't agree. This site I am referring you to is dealing with moisture problems in the home and not the basement, as in your case. This site points out air movement is the dominant source and I agree. For an example, if you have a forced air system with leaky ducts, it could produce the same problem. High pressure being attracted to a lower one.

Considering it is a basement and the way most people install insulation in this area, in my opinion, Equilibrium Relative Humidity is dominant. In construction, the way they avoid this moisture problem is to install a drainage plain. This is an air gap between the two different materials. They use this a lot with brick venere. In other words, build the wall two inches away from the masonry wall. You should never apply two vapor barriers. It will cause a moisture problem. The site discusses where the vapor barrier should go.

I know there is a company that sells fiberglass insulation with a vapor barrier on both sides. On the DOE site it discusses perms. This insulation wrapped in a vapor barrier has one side that has a five times greater perm rating than the other side. If you read that topic it will explain why this company sells this product. The "WC" stands for water columns and the rating labled on insulation for vapor barriers is SP-15. The "SP" stands for static pressure.

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