A.The simple answer to
the first question is yes, silicone caulk could be
used as an exterior glue. However, because
it’s not actually an adhesive, its
adhesive qualities tend to break down much sooner
than those of an actual adhesive.
In comparing different exterior adhesives,
it’s best to look at longevity rather than
strength. Initially, any good exterior adhesive
should be stronger than the material it is gluing.
Over time, with exposure to extremes of heat and
cold as well as moisture, the glue line begins to
deteriorate. Most one-part cross-linking adhesives
(for example, Titebond II) have a limited ability
to withstand the extremes encountered in an
exterior environment. Most will show signs of
delamination within 6 to 12 months. Reactive
polyurethanes tend to have better longevity
— sometimes as much as five or six years.
For the ultimate exterior bond, the unquestioned
best adhesive is a resorcinol resin. In documented
cases of over 60 years, this type of glue still