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Options for sealing rigid foam seams

HFF | Posted in General Questions on

I got a great deal on 25 psi EXP (I know, but the price was too good to pass up and essentially it is “used” foam ) that had been sitting around the yard for a while. Wall assembly: drywall, 2×4 with R15 mineral fiber, OSB sheathing, WRB (Benjamin Obdyke Flatwrap), foam, rainscreen, siding. Although my main WRB is between sheathing and foam, for several reasons I would like to effectively and inexpensively seal the foam seams. One reason is that many of the corners are rounded and some of the tongues flattened. I would prefer a caulk-type sealant over tape, to help fill in some of these small gaps, and also because I’m concerned with possible squeaking with day-to-day thermal expansion. Any suggestions? Foam sub-floor polyurathane adhesive seems like it might be a cost effective option. Would that work?
Thank you

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Replies

  1. brian_wiley | | #1

    Hi Fred,

    It seems like most sealants would do the trick, but I'd be most concerned with the sealant being compatible with the FlatWrap. The spec sheet allows for several compatible caulks and sealants. Cross-checking that with the compatibility of those with your foam should give you a couple of options.

    https://benjaminobdyke.com/wp-content/uploads/2020/10/FWHP_InstallGuide2020_Final.pdf

    Good luck with the project!

  2. Expert Member
    Akos | | #2

    Most foams shrink over time so caulked joints don't tend to hold up in the long term. Since these were sitting for a while, might be pre-shrunk so you might have better luck.

    I would get one of the single part foam guns and use that seal up the larger gaps and cracks than tape over the seams with a quality tape (Zip, 3M 8067). Much quicker than caulking a couple hundred linear feet.

  3. Expert Member
    BILL WICHERS | | #3

    I've used my foam gun for this before, along with tape using pretty much the method suggested by Akos. It works pretty well, but you'll probably have to trim some of the canned foam. DeWalt makes a little handle that will grab the end of a hacksaw blade that works great for trimming canned foam. Use a fine-tooth hacksaw blade to cut canned foam. I've found this tool does a much better job than a knife for trimming canned foam excess.

    Bill

  4. walta100 | | #4

    The smart move is to have 2 or more layers with staggered seams.

    You may find this article interesting

    https://www.buildingscience.com/documents/insights/bsi-036-complex-three-dimensional-air-flow-networks

    Walta

    1. HFF | | #5

      Thanks all,
      This issue of foam shrinkage is definately concerning to me, and I was unaware of it when I planned my assembly. Would as little as half an inch additional help to mitigate the problem? Can I use a different, more environmentally friendly foam (EPS or poly)?

  5. walta100 | | #6

    Get on YouTube and search “Lstiburek” watch about 4 hours of his talks. Likely to change the way you think about at walls.
    In one talk he mentions that he lost a lot of money in a SIP company because they could not make good enough joints between the foam panels in the field.

    Walta

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