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Community and Q&A

Tape separating from polyiso

mla12 | Posted in General Questions on

Last year we insulated a kneewall space with rigid foam (polyiso). The difference is amazing and we absolutely love it.

One small problem is I noticed the tape that was used across the seams is beginning to lift slightly. Photo attached. I don’t know what tape was used. 

Any suggestions on how to keep the tape edges down, short of re-taping everything? Is there a glue or adhesive I can apply across the tape to foil boundary?



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  1. Expert Member
    BILL WICHERS | | #1

    That’s a bit strange to see, usually tape sticks pretty well to foil-faced polyiso which is one of the big positives about using it. My guess is that the surface wasn’t clean when the tape was applied. Any grease or a lot of moisture will greatly reduce the adhesion of the tape.

    You can try pressing the tape back down again in case it wasn’t pressed firmly enough before. If the tape lifts again then you’ll probably need to retape it. A quick wipe down with a paper towel damp with isopropyl alchohol will clean any oils off the surface so the tape will stick well. Do a quick wipe down, then let it dry for a few minutes and you’re good to go with the taping.


  2. GBA Editor
    Martin Holladay | | #2

    Without knowing more about what type of tape you used, it's hard to give advice. If the polyiso has foil facing, housewrap tape should work. I think you'll need to re-tape these seams.

  3. Expert Member
    Dana Dorsett | | #3

    The adhesives used on foil tapes vary in quality & characteristics. For this application you need an adhesive good over a wide temperature range. The foil HVAC duct sealing tapes are pretty good (eg Nashua 324A, available at most box stores.)

  4. gawdzira | | #4

    To boost tape adhesion I used to use Scotch Super 77 spray mount adhesive a lot. On my last project where I had a guy installing Stego wrap plastic in a crawl space we found that the best spray for that situation was the Gorilla Spray Adhesive. Most likely, any of these type of spray adhesives will work. The tape companies usually sell a particular brand "designed" for their tapes that cost more if you prefer spending more money.

  5. Expert Member
    Peter Yost | | #5

    Hi Maurice -

    It's hard to pick an adhesive to "boost" the adhesion of what you have because the two have to be compatible.

    If either the initial pressure was insufficient or the face of the insulation had any dust on it, that could be the culprit (even surfaces that look dust-free can have a film of dust, I have found, so if the area to be taped was not wiped prior to installation, the tape can let go over time).

    Pressure sensitive adhesives need to "wet" to bond well and the lack of pores on an aluminum surface make for a more difficult bond. I would pick a higher quality acrylic PSA tape (such as 3M 8067) to cover the edges not adhering well.


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