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Vapor retarder paint doesn’t work with open-cell SPF – Reference?

pioneerbuilders | Posted in General Questions on

On 10/29/15, there’s a nice response by Martin that says, basically, vapor retarder paint has been proven not to work.  This was in response to the question, “Vapor barrier or vapor retarder paint on open-cell spray foam?”

The response mentions the proof came from Building Science, but I just can’t find the reference.

Would someone be able to direct me on where to find that?  Many thanks in advance.

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  1. GBA Editor
    Martin Holladay | | #1

    I got it from the horse's mouth. I had a conversation with Joe Lstiburek. Joe told me that Building Science Corp. tested the concept in one of their labs -- they painted cured spray foam and tested it for vapor permeance. He told me the paint didn't work -- the pores of the cured spray foam are too big for the vapor-retarder paint to be effective.

    He told me, "You first have to install gypsum drywall over the cured spray foam, and then you have to apply the paint the the drywall. Otherwise the paint isn't effective."

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