"Great Stuff" foam sealers

I was gonna seal the gap between my garage wall and the fireplace with some of that "Great Stuff" until I can afford the time to do a proper fix. My question, would having this foam on the OUTSIDE of the fireplace (i.e, the part of the fireplace that isn't exposed to fire and is in fact not even on the same side of the wall as the hearth) constitute a fire hazard?
The gap is immense and the drywall needs to be replaced as there is quite a bit of water damage.
If there are other options, what would they be. I estimate the gap to be roughly triangular, about 4 inches wide at the base.
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Eigenvector wrote:

That is what I used to seal mine up but I never use the fireplace. It doesn't get that hot there but if you are concerned go to a plumbing supply house and get some chimney cement or ask them for some non-flammable stuff.
Question? why is flammable=imflammable but possible<>impossible
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inflammable meant "it doesn't burn" that a new word, flammable, was made up to prevent confusion. No, really; look it up.
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If your gap is 4" you don't want that foam stuff. The gap is too wide. Sheetrock or plywood will work for a gap that large.
But otherwise it is not a hazard.
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If it is 4" wide, I'd stuff it with fiberglass, then put sheetrock over the top of it.
The foam may make it harder to do a proper repair later is it sticks really well.
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I am not sure what you are doing but if you can make it into somthing you can pour masonry into, consider Non Shrink Grout. We had voids between the concrete foundation wall and brick veneer and the mason who fixed it poured in non shrink grout. It is made for that purpose. Also used in factories so giant tools can be attached to concreter floor.

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