Was up in my attic earlier and noticed one of the mastic joints on my plenum was a touch damp and moldy. Anything specific someone here can recommend to remove that mold effectively enough to mastic over again and have it adhere? I’m going to scrape off and replace the mastic where I can, but unfortunately for me, it’s not super easy to access on all sides and would probably be much easier to clean and re-apply, if that’s viable.

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Posted by Spankum

Miss-sippi

Member since Jan 2007

58356 posts

Posted on 4/4/25 at 12:21 pm to GeauxldMember

I just turned off my unit and applied some of that aluminum duct tape to mine. It is still solid after ten years.

I don’t so much care about the mold in the attic. However, any air that leaks Lou of your A/C system into your attic, the same amount of unconditioned air is being sucked into the conditioned space in your house.

This post was edited on 4/4/25 at 1:19 pm

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Posted by GeauxldMember

Member since Nov 2003

4953 posts

Posted on 4/4/25 at 3:21 pm to Spankum

quote:
I don’t so much care about the mold in the attic. However, any air that leaks Lou of your A/C system into your attic, the same amount of unconditioned air is being sucked into the conditioned space in your house.

Yeah, I’m not worried about a little mold; the bigger concern is that I don’t want the loss of efficiency or the condensation the bad seams bring. I don’t think either the foil tape or the mastic will seal sufficiently until the mold is gone, and I don’t want to possibly break down the mastic by using bleach.

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