- Q.The specs for
spray-applied urethane foam insulation say that it does
not absorb water (hydrophobic). So why is it never used
on the outside of foundations?
contractor Patrick Dundon, of Windsor, N.Y.,
responds: Spray-applied polyurethane foam is
in fact frequently used as an exterior foundation
insulation. Foam Enterprises of Minneapolis, Minn.
(800/888-3342), has been supplying insulation
contractors with this system for several
Urethane will not absorb water, but if there is
sufficient force (a high water table, for example,
or improperly directed runoff), water will
penetrate the foam. In addition, urethanes do not
stand up to sunlight well, which means a protective
coating is necessary to prevent UV degradation. An
exterior foam insulation job requires coating the
below-grade portions with a cold-applied asphalt
and those portions above grade with an acrylic roof
coating or a cementitious EIFS-style parging.