Nussy said:
Well I emailed Dow to get the scoop on Great Stuff. There website says it's a "closed cell polyurethane foam" which is what most of the other stuff is that's used for floatation.
Here's the response " Great Stuff is used to block air infiltration into homes. The product is water resistant but the product is not water proof."
I think any foam used will eventually hold water. The stuff I cut out of my boat was the factory original and the bottom two inches were soaked.......but the guy stored it outside in the rain, with no cover and the foam directly exposed to all the elements.
I think you would be find using Great stuff in areas that won't be sitting in water. My suggestion would be to use the pink building foam between the ribs on the floor. It's easier to work with and cheaper than the foam. Then use the foam in areas above the floor like a seat, etc.
Nice detective work.. I would have guessed they'd give an answer like that.
I'd go along with what you said though.. I think spray foam should only be used in places sheet foam cant, or in areas that are sealed from water. While I've never had an issue with great stuff getting soggy etc, its probably better not to risk it.
Plus sheet foam come in varying thicknesses, making it perfect for putting under floors.