Join Date: Jun 2004
Location: West Michigan
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If the foam is adhered to the hull, there won't be any condensation at the junction, simply becasue there is no air space. As long as the 'skin' is undisturbed after application it is waterproof.
That said, I don't think I'd want it sprayed into a steel hull simply bacause it can't be removed for inspection etc.
The sheet stuff works great because it can be removed easily and is waterproof for the most part. Bad part is that since it is a sheet there WILL be airspaces between foam and hull so you can easily get condensation.
A method I've used with spray foam to make it fit tightly yet be easily removed, is to make sure the cavity it's going into is smooth, then spray the foam into plastic 'bags' you make from sheet plastic and tape. The plastic keeps the foam dry and prevents it from adhering to the hull, so it's easy to pull out for inspection or maintenance.