Just trying to solve a question. After sealing ducts with foil tape, could you then cover that with mastic? Would this application cause a failure in the tape adhesion? By the same thought once mastic is applied would you use foil tape over it?

Any thoughts would be appreciated

Mastic, I looked the word up,and what I saw it doesn`t sound like something I would want to put around my ductwork. maybe better explain would help.;)

Either foil tape, or mastic duct seal is fine, but I wouldn't use them together. I would suggest using duct seal, as it will hold up longer when properly applied. Why would you use them together? Never heard of that before.

I would think that putting duct seal over foil tape could cause the tape to moisten and not hold. And I don't think foil tape would stick on top of wet or dry mastic. That make sense?

We do a lot of installs and use screws, foil tape then mastic (we call it pookie). Just make sure the pookie covers all of the tape and has a solid sheetmetal area to cling to. It holds up great in AZ with 140 degree attics. If you need extra bonding in the pookie there is a mesh you can use. It is almost like what the drywallers use on thick joint compound.