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Community and Q&A

Does Polyurethane foam degrade rigid EPS?

GBA Editor | Posted in General Questions on

I was planning on using Dow’s Great Stuff polyurethane foam sealant to air-seal home-made EPS wind stops in my rafter bay ends to my roof deck & air chutes.

A salesperson at my local building store warned me that polyurethane foam would eventually degrade my EPS wind stops. I have been having trouble confirming this on Dow’s website.

If this is true is there another type of sealant that would work better in this situation? Thanks for your help yet again.

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  1. GBA Editor
    Martin Holladay | | #1

    There is no compatibility problem between canned spray foam and EPS or any other rigid foam.

  2. Riversong | | #2

    Some canned foams use isobutane, propane and dimethyl ether as propellants (highly flammable). If there is any degradation of the XPS, it would be only during initial application. Once cured, the two foams should be perfectly compatible.

    Canned foams are routinely used to seal XPS and other rigid foam boards.

  3. Riversong | | #3

    I should add, though, that if you're using large quantities of canned foam to air seal your house, it's well worth investing in a foam gun (available at most building supply houses) and using the screw-on canisters (available in high-expansion, low-expansion, and fire-retardant varieties). Application is much more controllable and there is much less waste. A partially-used canister can be left on the gun for months.

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