Is Spray foam insulation watertight? (with pic)

Old 08-21-17, 04:34 PM
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Is Spray foam insulation watertight? (with pic)

Would water seep thru between the foam and concrete; and foam and pipe? Do I have to put silicone caulk to glue the foam into it's surround to make it watertight?
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Old 08-21-17, 04:45 PM
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Good question, however the answer may be somewhat ambiguous.

Most spray foams like you have pictured are closed cell foams, which have a low permeability, and are therefore classified as "waterproof" by the manufacturer. In other words, submerge the foam in water and it should not absorb it like an open cell sponge would. However, diy spray foams are not the greatest product to use where waterproofing is needed.

The substrate that the foam adheres to cannot dry out should it become wet, and this often will eventually degrade the bond between the foam and the substrate. So if foam is being used to stop a leak... that fix is often only a temporary one.

Sealants are much better suited for such a task because of their superior adhesion and longevity.

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