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Can I spray foam over foam boatd

dannnyb | Posted in General Questions on

I recently added rigid foam board to the concrete walls in my crawls pace.    Not the most perfect job.  I’m Having the rim joists spray foamed and the insulator suggested tearing  out the board and spraying the walls to better seal.   I am reluctant.   Can we just spray over the existing foam board?  Will thisleadto moldproblem?

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  1. Expert Member
    BILL WICHERS | | #1

    You can spray foam directly over foam board without problems -- I've done this myself in the past. What you want to avoid is voids where moisture can accumulate, so if you put a thick layer of spray foam up, you want to make sure the foamboard doesn't pull away from the wall. If you have thin foam board (less than an inch or so), it will be more likely to pull away and create voids. You can improve things regardless of the thickness of the foamboard by installing additional anchors to hold the foamboard tight to the wall.

    Note that you're safer using closed cell spray foam here, since it's better at blocking moisture, but you need a thick enough layer to form a vapor barrier.


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