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Community and Q&A

EPDM roof bubbles – problem?

owenqs | Posted in General Questions on


I have just completed a small EPDM flat roof. I used a new adhesive onto tissue faced PIR that didn’t adhere particularly well, I believe the tissue faced absorbed a lot of the adhesive. I did let the glue flash off so I don’t think off gasing was the issue just lack of adhesive in spots. 

Anyway, I am now left with a very bubbly membrane. My question, is this a technical problem or just visual? Another builder on site says I’ll get condensation on the underside of the bubbles which clearly would be a problem. But is that true if it is cold/cold on both sides? And there is no moisture on the inside of the EPDM? 

Climate 4C
Build up Inside to Out: Drywall, Intello Air/Vapour membrane/ 8-10″ rockwool between rafters, T&G OSB, 3″ tissue faced PIR, EPDM. 

It is only a small dormer flat roof and will never be seen so if it is visual only I am okay with it (reluctantly).
Thanks for your advice

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  1. gusfhb | | #1

    That is some bubbles.

    I am not sure what tissue covered is, here we have fiberglass paper scrim for roofing

    I have some areas where I have some bubbles due to the large sheet shifting on the low slope roof and 12 years later it is not a problem.

    Looks like you did not wait long enough for the glue to dry.

    Weirdest thing to get used to when doing EPDM as an amateur is walking on the adhesive as you pull the sheet toward you

    Have you tried rolling to see if you can take the sin off the bubbles? Might still work, not completely but maybe better

  2. owenqs | | #2

    Hi - yes I've tried rolling it back out but it isn't helping! Perhaps I didnt wait long enough, the EPDM side adhesive would try almost immediately but maybe the insulation side took longer.
    My concern is really just whether or not the air gaps would result in condensation or something else that could cause long term damage.

    1. Expert Member
      Michael Maines | | #3

      I learned about EPDM bubbles the hard way, over 20 years ago when installing it on a third-floor deck. It went down fine but when I came back the next day it was full of bubbles. In a fit of frustration I tore it all up and started over. Then I learned that the contact cement offgassing caused the bubbles and they would eventually settle down.

      While not ideal, there is little danger of condensation, since there shouldn't be moist air under the EPDM.

  3. owenqs | | #4

    Thank you Michael. Interesting to learn from you both! Next time, wait longer!

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