Sealing Vapor Barriers to Concrete Foundations

Replies to This Discussion

Permalink Reply by James Canter on June 4, 2012 at 8:23pm

I use CCA treated furring strips and mastic in the caulking tubes. Wrap the plastic around the strips, apply mastic, and fasten to the block with a hilti gun. Time consuming but it seems to work.

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Permalink Reply by Tripp Pankey on June 6, 2012 at 6:57am

Tim,

I have used a recommend a product from crawlspacerepair.com called "Foundation Seal Tape".

It is a very strong and tacky double sided tape that is also waterproof.  I apply it continuously around the crawlspace about 3" below the top.  I use 15 mil poly that goes down the wall and then across the floor.

The tape seals and temporally mechanically holds the barrier in place until I ADD mechanical fasteners every 2 feet for  permanent bond.  

I highly recommend this product.

Tripp

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Permalink Reply by Ron Jones on June 7, 2012 at 8:53am

I use the same mastic I use for sealing ducts, in my case Air Seal polymer adhesive.  Brush on a thick layer, then attach to the foundation wall as James describes.  I also use it for the laps across the crawlspace floor.  I don't trust the tape that Tim mentions.

I'm of the opinion that mechanically fastening the furring strips is a necessary, time consuming, and therefor costly step merely to insure the vapor barrier stays in place till the mastic dries. Once it dries, your not pulling the VB off without some effort.  If I come up with an easier alternative to temporarily hold the material in place, I'll test that theory and get back to you.

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Permalink Reply by Patrick Michaelyan on June 8, 2012 at 4:22am

Tim,

I imagine you're using foam on the walls in the crawl space? If so, I have recently switched to foaming over the vapor barrier. It has been a very effective approach, assuming someone doesn't crawl through the space like a bat out of Hell and rip the barrier off the wall.

I run the poly up the walls (about 6 inches) and spray over the poly, and spray especially thick at the interface of the walls and the floor of the crawl.

Just my take on this, given personal experience and a genuine concern for the cost of projects getting out of control for the average HOs.

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Permalink Reply by Pat Dundon on July 26, 2012 at 5:18pm

Don't use poly, use EPDM roofing material. Then you can use sprayfoam to seal.

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Permalink Reply by Patrick Michaelyan on July 27, 2012 at 7:11am

Pat, about what are you paying per square foot of the EPDM membrane? I assume you use a roughly 60-mil product?

Thanks in advance!

Patrick

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Permalink Reply by Pat Dundon on July 27, 2012 at 4:57pm

The EPDM can be purchased at 40 mils and 60 mils. I use the 40, over the past couple years we have paid between $0.80 and $1/sf for it. We buy black material. The white is much higher cost. It is very unlikely that it will see any sunlight or wear, so i see no reason to go thicker.
We usually spray foam fom the subfloor down on th EPDM and at east 4 ft in long the bottom of the wall and seal all joints. I am in upstate NY, 7000 HDD, so frost penetration under the wall governs how much of the floor we spray. I usually spray the whole floor if the space is less than 16 ft across. That is an arbitrary choice.

I do know of one job where the owners decided to tear down the existing house and put a year round residence in place of it after we did this work. he is a friend of mine, and he called to tell me demolishing the house was easy with an excavator until they got to the crawl space. Apparently the EPDM stretched enough so the excavator could not pull far enough to pull it loose from the block. In the end it pulled the blocks out still attached to the EPDM.

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Permalink Reply by Patrick Michaelyan on July 28, 2012 at 8:47am

Impressive story Pat.

Thanks for the info on the EPDM!

I think you may have made a convert out of me (from poly vapor barriers to EPMD).

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Permalink Reply by Ed Minch on August 2, 2012 at 10:44am

The foam manufacturer's make an extra sticky single part foam - same chemicals as the air sealing foam, different proportions.  We use Convenience Products Foam and they make one called Panel Foam.  This sticks the plastic up quite well, then we use it stick 2" board on the wall overlapping the plastic by a foot or so

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Permalink Reply by Pat Dundon on August 2, 2012 at 11:19am

i haven't heard of this before.  as far as I know all urethanes are 1:1 ratio, so i would sooner believe the resin/iso mix is 1:1, but the chemical reaction time is slowed a lot. 

have you gone back to one of these a month or further after install to see how the adhesion is? 

generally we get worse results with single component and dual component 'portable' or 'unheated' kits than we do with plural component heated kits.  those electric wraps for the cylinders are well worth the cost and hassle. 

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Permalink Reply by Ed Minch on August 2, 2012 at 2:15pm

Pat

I have no doubt that the ratio is 1:1, but not all are the identical formula.  We have been doing this for about 10 years and have had occasion to get back in to see up to 3-4 years later - no problem.  The 2 inch board is not extruded styrene but iso board with faces on it.

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Permalink Reply by Richard Scott Mills on August 9, 2012 at 9:20am

Any problems w/ VOC in crawl space during application or migration to home through floor?

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