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Crawl Space Dilemma (Visqueen, water and efflorescence)
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Source：Internet Author：Unknow Pubdate：2008-03-27
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DBJB (Structural)
31 Mar 07 18:09
Hi there. The house is in a coastal area (west coast) with a high water table and a dirt crawl space. After taking the recommended steps to limit water under the house (sump pumps, drainage away from the house, etc.), I installed 6 mil plastic sheeting over the entire crawl space. Shortly after we completed installation, there was noticeable efflorescence on the cement piers (sides and top) and on the foundation walls (both inside and outside). After brushing off the piers, I continued to inspect the crawl space over the next week - thinking that it would taper off - but the efflorescence build-up continued. It seems as if the plastic, acting as a vapor barrier to the soil, has limited the evaporation under the house to water vapor through the concrete piers and foundation walls. I assume that the concrete structures are now acting as wicks for the water to evaporate because they are now the only possibly place for the water to go (evaporate). 字串6
So now what? Should we remove the plastic sheeting and allow natural, evenly dispersed evaporation through the soil or keep the plastic sheeting at the risk of water damage to the wood which abuts the concrete piers and foundation walls. Or, maybe there is a third option? Any ideas would be greatly appreciated!
emmgjld (Geotechnical)
3 Apr 07 1:02
I have dealt with a similar problem. I usually recommend the ground cover be folded back from the foundation concrete about 2 feet. You will accumulate a lot of sulfates in this area but, the wicking up the concrete is usually minimized. I also recommend increasing the crawlspace ventilation to cut down the odors. If you completely remove the ground cover, the humidity in the crawl space may increase and overwhelm the ability of the existing vents to remove excess humidity.
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