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Can you apply spray polyurethane foam over mold in a cathedral ceiling?

2wBzrWjBUK | Posted in Energy Efficiency and Durability on

I am renovating my second floor bedrooms and plan to apply spray foam to the 2×6 ceilings (cathedral). The old batt and baffle system was not installed properly and there is some mold in the sheathing and the 2×6’s. I’ve read that the heat generated from the spray foam kills the mold.


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  1. jklingel | | #1

    Were I permanently covering mold, I would get a reputable mold company to really make sure it is nuked before I covered it. Wash it clean, disinfect, let dry (maybe even watch it a while), then cover it. Said company may even suggest tearing off the roofing and killing the mold on the outside. I don't know molds well, but I believe some (like on bread) can "dig in" quite a ways.

  2. Danny Kelly | | #2

    Heat will not kill mold. I would remove it prior to covering it up. Mold is also a sign of a moisture problem - be sure to solve your moisture problem before moving forward.

  3. 2wBzrWjBUK | | #3

    The moisture problem will be solved, I think, by changing the insulation method to spray foam from fiberglass batts. The interior has been gutted so the ceiling joists and sheathing are exposed so everything has been able to dry out. Doesn't mold need moisture to thrive? At this stage the mold is not growing any more correct? Any tips on a diy solution to the mold besides bleach. Have to keep my costs down so hiring someone doesn't work for me. Woud kilz or zinser trap the mold and keep it from growing any further? Would spray foam serve the same purpose? Not trying to cut corners but need a frugal way to approach the issue. Spray foam has to be done with the limited space I have to insulate. Live in Michigan so the temp gets pretty low. Thanks for your thoughts and time.

  4. jklingel | | #4

    OK, if you are diy-ing it, wash thoroughly with soap and water, then bleach or a moldicide (I just made that word up) if you can get a solution specifically for mold . No more than 10% bleach is needed, and don't use old bleach. It does expire, and you can call the company to find out if your bottle is still good (infection control in hospitals use bleach, and 10% kills all their kooties). If you are positive the outside of the roof is dry and mold free, you should be good to go. Yes, mold needs water, but it can hang around dry for a long time, as far as I know, so try to kill it. Be careful breathing it, if you do anything around it when dry. Some people are very allergic to mold. My son's throat almost closed on him when he disturbed mold in an old apartment building.

  5. MJDesigns | | #5

    See the following link:

    You can always contact them as well for more details.

  6. Foamer | | #6


    Professional spray foam equipment applies the foam at relative high pressures so you need to treat the mold before you insulate. If you don't, there is a good chance that you will blow mold spores all over your attic and from there, the rest of your house.

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