Q. What’s the difference between polyurethane construction adhesive and polyurethane caulk? In a pinch, can polyurethane caulk be used as an adhesive?

A.In a pinch — yes, but I wouldn’t make a habit of it. While adhesives and caulks share the same resin (polyurethane), they are formulated for distinctly different purposes. In the case of wood, glues form the best bonds when they penetrate and wet the two parts, then cure to a hard, rigid solid. On the other hand, caulks are expected to "cling" to two surfaces (often of dissimilar materials) as well as to bulk up and fill the gap between them. This requires a less rigid and more elastomeric substance, so the caulk is loaded with fillers and additives that allow the caulk to move when the joint is stressed, then return to its original shape.

— J.J.