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Insulation causing concrete to crack?

Jeff_Garnelis | Posted in General Questions on

Hi all,

I plan on installing 2inches of GPS rigid foam to the inside walls of my foundation. While talking with my plumber, he mentioned that he was recently on a job where they were removing interior rigid foam insulation on a foundation and noted excessive cracking everywhere there was foam. In the unfinished portion of the basement and in the mechanical room where there was no rigid foam attached to the wall, there was no cracking.

Is this something I should be concerned with? Crumbling foundations due to excessive levels of pyrrhotite are common in my area so my hypothesis is that the job had a bad foundation to begin with and the rigid foam along with any exterior waterproofing caused a double vapor barrier for the concrete and expedited the failure rate. Just a guess though. Thank you in advance.



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  1. Expert Member
    Michael Maines | | #1

    Jeff, I have never heard of that being a problem, and I almost always insulate foundation walls on the interior. In fact, keeping the concrete walls damp, as foam will contribute to, allows them to continue curing and get stronger over time.

    If the concrete is not air-entrained you could potentially get some spalling, but that would be more likely to occur on the exterior than the interior.

  2. Expert Member
    BILL WICHERS | | #2

    I wouldn't expect the interior rigid foam to be a problem that would cause excessive cracking by itself -- i.e. foam doesn't damage concrete. It's possible there were water issues though, and freeze/thaw problems CAN fracture concrete block foundation walls. If you have a poured concrete foundation that shouldn't be a problem though.

    Ideally you waterproof foundation walls on the exterior, but if you're concerned, you can use a dimple mat on the interior behind the foam to provide a drainage plane that will eliminate any issues with water potentially building up within the foundation wall itself. I have one part of my own basement that is a block wall, and I've had water issues with it in the past. When I insulated it with EPS, I used some DMX 1-step as a narrow (~3/16") dimple mat against the wall behind the EPS panels, then I secure the EPS with long tapcons through the foam into the block. The dimple mat allows any water that weeps through the wall to drain away, ensuring there are no issues with water buildup within the wall. That could work for you too. I did seal the top and side edges of the dimple mat with polyurethane so that only the bottom is open.

    It's possible the foundation your contractor saw was already damaged, and someone installed rigid foam over the damaged sections as a way to conceal the damage. Another possibility is that when the foam was removed, the remaining pieces that were attached with adhesive were chipped off and took a little of the concrete surface with them. That should have been minor, but would have made the wall look much worse than it actually was.


  3. Jeff_Garnelis | | #3

    Thanks for the responses.

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