Duct Tape... Uses and Abuses
Loving duct tape means never having to say you're sorry... when it fails!
I was, at one point in my career, a duct tape addict. I would lash together lumber, repair hammers, fix my trusty wooden tool box... ad infinitum. Then, in my travels through thousands of homes, I came to see the weakness in duct tape as some repairs done with it days, weeks or months before began to fail. The weakness in duct tape's armor is due to three factors... poor adhesive quality, heat and ultraviolet light.
The adhesive used on duct tape is tenacious. If you've ever torn off a piece and had it touch itself, you know the meaning of sticky! Straight to the garbage can for that strip, yessirree. But as strong as this adhesive is, it is not really permanent like a setting-type adhesive. And some "bargain basement" duct tapes are not worthy enough to wrap fish!
Heat can soften duct tape adhesive, making it lose strength. If there is weight or stress on the repair, this softening can cause the tape to slip and the joint or attachment to fail. This can be prevented by use of a secondary fastener such as a clamp or strap. A classic example of this faux pas happened to a customer of mine a number of years ago...
I don't have the trust in duct tape I once had. So as a rule, unless I am looking for a temporary repair, I always find a way to supplement the strength and air-sealing properties of duct tape with a more permanent fastener!
Can I use duct tape outside?
Duct tape for the most part is not meant for exterior repairs unless it is specifically labeled UV-resistant. The problem is sunlight, which causes the plastic that ties the tape's threads and adhesive together becomes a dust-like skeleton over time. (Hat tip to Randy of Feather River Canyon News, who called it "a powder-coated set of threads with dried up adhesive." ) Even so, these tapes are not "forever" so I would consider other fastening methods if you are looking for permanence in areas exposed to sunlight.
For example, Scotch® has a variety of special-duty "All Weather" duct tapes. They claim triple the life of standard duct tape, which I don't doubt and is a great improvement... but I would still consider it a short-term or emergency repair solution in exterior, sunny areas.