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Do I need mastic here? – GreenBuildingAdvisor
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Replies
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Chris_in_NC | | #1
Did mastic not get applied to the seams on the exterior side? It’s generally easier to apply on the outside, rather than crawling inside the ductwork.
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kickstarter | | #2
This duct enters the attic. The portion that’s extending out into the home doesn’t have mastic on the outside anywhere. I’m assuming its not on the exterior on the attic side either.
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Expert Member BILL WICHERS | | #3
If it’s well taped, you’re fine. Tape is an acceptable way to seal ductwork too, mastic just works better in some cases (especially old ducts). It’s not usually necassary to seal corner seams in fabricated ductwork, but it doesn’t hurt. If you can’t get access to use mastic on the exterior, I’d use foil tape (Nashua 324A is my favorite for this). Normally you’d tape on the exterior. I would be reluctant to use mastic on the interior of the duct myself.
Bill