Saturday, April 18, 2015

Tape is Tape NOT!

I must admit that when Glenn Walter of Shurtape offered to do a presentation on duct tape application for my class I thought “Oh HOW exciting!” (Yawn) After all, how much can there be to know about duct tape? It can’t even connect to the internet! But then I really hate to turn away help and I like having people from the industry come talk to my students, so we set up a class. One thing I have come to understand about life in general: whenever I think there is nothing to know about a particular subject, it is only because I know so little I don’t understand how ignorant I truly am. When Glen started his presentation I quickly realized that there is whole lot to know about duct tape. What follows is a cliff notes version.

Duct tape consists of a backing and an adhesive joined together. There are four types of backing: cloth (the old standard), film, foil, and foil-skrim-kraft (FSK).  There are two large categories of adhesives: acrylic and rubber based. Most techs know that codes require UL 181 tape. However, did you know that there are two general categories of UL 181 tape: 181-AP and 181-FX.  AP is rated for use on rigid ductboard and FX is rated for use with flex. Note that there is no specific UL rating for tape on metal duct systems – UL 181 is for ducts made out of manufactured materials. You may have also seen tape with a UL 723 rating, which is a smoke and flame spread standard. It makes a difference WHICH UL rating your tape has. Just because you see UL does NOT necessarily mean your tape is correct for the job. Even two tapes with the same UL rating can have different application specifics. Also note that the UL rating is not based on the backing or adhesive, but the tape performance in specific tests. Shurtape has 181-FX tapes with foil, film, and cloth backing with both acrylic and rubber adhesive. They are all approved for use with flex duct, but each has a specific application where it is better. For example Shurtape’s film backed tape with acrylic adhesive is rated for application between -20°F and 220°F. Their other FX rated tapes won’t stick at -20°F.

Most codes now require mastic for sealing metal ducts, but many people still use tape underneath the mastic. Did you know that many duct tapes are not rated for that use? Mastic does not stick well to film tapes. Not all cloth tapes play well with mastic because the chemicals in the mastic and the chemicals in the tape adhesive may not be compatible. The cloth tape might turn loose, then having the tape underneath the mastic just creates a place where mastic is not fully adhered to the duct. Foil tape usually does fine under mastic.  You should check with the tape manufacturer before using a tape underneath mastic.

Finally, the tape application is not complete until you apply pressure. For foil backed tapes, a plastic tool with a stiff rounded edge is preferable for working the tape into the duct. The pressure is needed to fully activate the adhesive on the tape. The adhesive undergoes a chemical process, similar to glue setting. Duct tape is not fully adhered until this process has been started through pressure application and completed with time. Believe me, there is a LOT to know about duct tape. If you would like to learn more, contact Glenn Walter of Shurtape at

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