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dbtothadb

Mastic or Duct-Seal for outdoor duct?

dbtothadb
5 years ago

We have a section of hvac duct that goes across the flat roof of one room of the house. It has started leaking, and my best guess is there is a crack or hole somewhere along the hvac duct. The duct has two layers of duct-seal on all seams and corners (probably one layer when it was installed, and another when it sprang a leak, both with previous homeowner).


Right now, I'm thinking the duct-seal may not be weather-proof for both sun and rain. I'm wondering if it's ok to use Henry Wet Patch mastic to try and patch the duct? It seems like it's made more for outdoor use, given that duct-seal is water-based. It really looks like every possible leaking point was patched with whatever is on there (likely duct-seal) and it's obviously not working.


The attached photo shows the duct, with what I think is duct-seal type product on the seams, and a giant patch of Henry on the roof below it (we now know that the leak isn't occurring in the roof, but within that near corner of the duct).


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