Q.Can silicone caulk be used as an exterior glue? How does it compare in strength to Titebond II or a polyurethane glue?

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 remains durable.

— J.P.