# Problem with spraying hvac ducts?



## zorikos (Aug 31, 2011)

I recently sprayed a new metal deck ceiling and noticed a few areas on the hvac ducts the paint cracked/blistered. I used SW acrylic dryfall and it doesn't state that it needs any primer. What gives?


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## tubtime (Jan 1, 2013)

oil left over from making/forming the ductwork?


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## Pete'sfeets (Mar 20, 2011)

Even the primer made for it can get repelled. Dryfall tends to shrink substantially though compared with other paints, a pail goes how far?


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## Pelican (Mar 4, 2011)

I second the residual oil comment and think ductwork needs to be degreased for anything to stick well


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## Pete'sfeets (Mar 20, 2011)

I tell you a story, maybe it'll make more sense, I painted a metal deck once that looked OK but really it was filthy, I sure as heck wasn't washing no 60'000 sq ft of ceiling, so I used primer and it stuck fine. Then I read the info on the dryfall and saw it had excellent adhesion.. But you know a gallon of dryfall only goes 100 sq foot, primer does 400sq.. So my theory was that when I put the dryfall over the primer, well It shrinks so well that the shrinking just pulled a whole lot more as it dried and pulled itself right off the substrate which was super baked on dirt really, Had I just stayed with primer I'd have been fine .. Now that you hear the story, stop and realize that I was trying to clean up the ceiling on a sixty year old factory, a sensible investor would have torn it down, so I didn't get sued, I just stopped painting the ceiling after the first 5000. My point is the dryfall though it has excellent adhesion , it may not be wise for flexive HVAC or dirty decks ,( of course ). But if you just stick with regular paint and primer , sure it gets some paint on the floor but if it is twenty foot up so what? I don't know if you can get anything out of that....:blink:


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## overanalyze (Dec 28, 2010)

We have sprayed a few exposed ceilings and ductwork. We always use an oil primer....the fumes suck, but it bonds to everything! We have one to do this month. We are going to try a new oil based primer from Sherwin Williams. It's an oil resin primer that cleans up with water....I will post our results once finished.


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