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I have some ductwork has been getting rusty because of condensation and I want to seal it with duct sealant and thin insulation on the parts that sweat/wet. Do I have to sand the existing rust off or can I just seal over it and stop the rust? Will it continue to rust more under the sealant?

It's difficult spot to get to with sanding and I'll have to open up the wall and cut through pipes if I want to get the angle for sanding, whereas I can probably get the duct sealant liquid and thread the insulation on to the spot using a thin brush, wires and gravity.

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So it's a much smaller job if I don't do the sanding.

MonkeyBonkey
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2 Answers2

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Use a rust converter. Be careful to get the proper product that chemically alters rust to make it non oxidizing, and not just a metal primer that covers rust. Example is here: Rust Reformer

Credit to Hot Licks for the original suggestion.

Amazon Dies In Darkness
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RMDman
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I found an article on your question in case you haven't seen it yet: https://azrust.com/clear-coat-over-rust/ In my personal experience, if rusted badly enough, the paint or sealer will flake off if the rust is flaking off (as you probably know). If this were the case, I would suggest going at it with a scraper, at the very least. You probably don't want to cut through the wall, but you should ask yourself if you don't do it now, is it going to be more work later? Although if the ductwork is bad enough, replace it, as 'RockPaperLz- Mask it or Casket' suggested.

Deyja S
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