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Guy who makes things
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Discussion Starter · #1 ·
Hey guys first post here and I'm hoping to get some advice on moisture control. I own a small plumbing shop, and we do light remodeling here and there as well, mostly 2 or 3 piece bathrooms in basements. Part of our standard procedures have been to apply 2" XPS with Z furring around the perimeter of the basements that we've been working in, sealing the band joist with XPS and expanding spray foam to seal up the joints. Generally, after hanging drywall on the Z furring, the humidity and moisture levels inside the basement improve dramatically.

The question that I have has to do with a customer who's approached me about what should be a regular job. His foundation is built out of 8" CMU and has about 4 layers of old peeling latex paint on it. The humidity down there is awful, it hits you as soon as you walk in. There's no water pooling, but the amount of moisture seeping through the foundation has obviously made the paint peel and even rusted out the steel hardware on some built in cabinets in one corner.

Will XPS applied over the foundation effectively manage the humidity? Or should I strip the paint and use thoroseal before putting up the walls? The difference between is going to be a major factor in how I cost the job out, which is why I'm asking.

Thanks a lot,
Keith C.
 

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I don't think the z furring is the way to go, I think it would have to eventually rust out. It would probably be better to use tongue and groove XPS, or two layers with staggered joints and going with metal studs over the XPS. This would also allow for easier electrical runs.
 

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Box Builder
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I've used thoroseal (sp?) on the outside of a foundation but not the inside. I would be more inclined with such a big problem as this to fix the problem where is starts, which is outside the foundation wall. If you stop extreme moisture and humidity at the inside face of the masonry wall it will go up into the sills and joists. If they are PT then I wouldn't worry too much. But if they are older typical 6x6 etc. it could speed up their deterioration. I also don't like to use XPS above grade where I know it will be getting wet or damp. In your case it's also inside the building envelope. It provides too good of a home for ants and bugs. I like borate treated EPS instead. Don't know exactly what the safe bet would be for your attack, but I would definitely include a dehumidifier for this guys basement. I would get rid of the paint on the walls thoroseal or not.
 

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Guy who makes things
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295 Posts
Discussion Starter · #5 ·
Thanks for the advice - I'm glad to have a few more options. I'm gonna examine his exterior grading, maybe see about checking/fixing his downspouts and drainage.
Thanks
Keith
 
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