Waterproofing corners where basement floor and wall meet?

tigerninetyOctober 8, 2012


We're moving toward finishing our basement (2x4 framed, insulated, drywall, etc). We've had some minor seepage issues in the past and are taking a multi pronged approach to water management; we're making a lot of progress. (Significant regrading outside away from house; heavy-duty plastic sheeting attached to house to five feet out covered with mulch; new window wells with covers; sanded interior cinderblock walls that will get new coats of drylock).

In a recent rain, however, I noticed a couple of places where there was a small amount (about one foot long) of dampness where the floor meets the wall. I'm going to redo the plastic (upgrade to 20-mil and double attach to side of house), but I was wondering if anyone would/could recommend some kind of sealant that works particularly well at this intersection of basement wall and floor?



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I've used Tremco Permaquik 300 as cove sealant on the outside of the wall/footing joint. All inside "solutions" will be less effective than stopping water before it enters your basement.

When finishing your basement walls, it is important to use moisture tolerant materials, such as EPS or
XPS foam board insulation in the correct thickness and XPS under the baseplates.

Here is a link that might be useful: Bulk Water Control Methods for Basements

    Bookmark   October 9, 2012 at 9:58AM
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Thanks for all of the above, particularly the link to the PDF. A couple of followups, if I may...

First, based on your post and the content of the PDF, I think I'd lean toward XPS (or EPS? difference?) against MOST of the cinderblock walls with 2x3s to frame, and additional, unfaced batt insulation before the drywall. This would primarily be to facilitate running electrical and for a cleaner look, relative to going with the XPS and furring strips followed by drywall. Also, the DOE calculator recommends R-11 in the basement in the Washington, DC area. Am I missing anything here?

Second, however, there is a section of wall where I think it would make sense to go with XPS held in place by furring strips (drilled into the wall) followed by drywall. But the 'DIY-assistant' I'm working with seems to dislike the idea of making holes in the cinderblock walls if it can be avoided (to reduce seepage risk, etc after dry lock). Is he being overly sensitive to that?



    Bookmark   October 10, 2012 at 7:23AM
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EPS (expanded polystyrene) is the lighter weight less dense material used in EIFS stucco systems and coffee cups. Because it must be thicker for the same R factor, it's not used much in inside applications. But it's cheaper.

I, too, hate making holes in concrete block! If it's a straight wall, adhesive can be used with fewer anchors. And when you anchor, drill into the ribs.

But it's very important to have the foam boards tight to the foundation wall. A neat trick John Straube of Building Science told me of is to use cedar shims between the boards and the framing.

Here is a link that might be useful: Building Science Corp: Basement Insulation Systems

    Bookmark   October 10, 2012 at 11:48AM
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Thanks again for your posts. I apologize if this is covered elsewhere, but if I'm putting XPS/EPS on the cinder block walls, then 2x3 framing, with batt insulation and then drywall, why NOT use faced batt?

My builder guy seems to think faced batt would be best "just in case" re: moisture.


    Bookmark   October 23, 2012 at 6:22PM
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The faced batt acts as a vapour barrier, trapping moisture inside the wall, especially in the summer when the hot outside air moves toward the cold inside air in your basement. (See BSC link below for detailed explanation.)

Vapour barrier and fiberglass on basement walls spells mould.

Since you're insulating the basement, don't forget the rim joist area at the top. Pull out any fibrous insulation; air seal with spray foam and/or caulking then use closed cell polyurethane spray foam or cut XPS to size, press fit and caulk.

Photos: Building Science Corp.

Here is a link that might be useful: Basement Insulation Systems

    Bookmark   October 23, 2012 at 8:18PM
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Thanks for the reply.

Please forgive my persistence on this, but I'm sure I'm going to have to work this further with my builder-guy.

I get the idea about the movement of vapor in the seasons. So, I WILL use XPS against the cinder block, followed by 2x3 framing. So, based on what I understand, the XPS is performing the role of vapor barrier up against the cinder block. AND it is ensuring that the vapor from the INSIDE doesn't have a cold surface (eg bare cinder block) to condense on.

My question (and I'm fine with the unfaced batt, but my builder-guy seems perturbed by it) is: if I've got the XPS as vapor barrier and insulator, how is the facing (toward the interior) on batt doing harm? Exterior vapor shouldn't get through the XPS and (in theory) interior vapor shouldn't even make it to the XPS.

So, I'm sure I'm missing something, what is it?

Thank you!


    Bookmark   October 27, 2012 at 8:32PM
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