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General control line discussion => Open Forum => Topic started by: Robert Zambelli on August 22, 2022, 10:25:07 AM
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Odd thread title but here's the story.
I noticed the paint bubbling on the nose of my Argus so I decided to strip and refinish it. (I had refinished it around ten years ago)
When I started to peel off the bubbling paint, I noticed what looked like Elmer's glue underneath.
It was not Elmer's - it was VERY sticky and a real mess. Not soluble in water but alcohol and lacquer thinner seemed to remove some of it.
Bursting one of the bubbles made made the white stuff squeeze out like toothpaste - as I said, MESSY.
The finish was nothing special - I have been using the same process for many years on at least ten different aircraft.
Brodak clear dope, sanded between coats, a layer of .5 ounce fiberglass cloth doped on, a few more coats of clear, then color and finally a few coats of clear, all sprayed on.
The inside of the cowl, tank and engine compartment were coated with finish coat epoxy and given at least a week to cure.
The Argus looked beautiful for many years before this nonsense started.
I'm puzzled - anyone ever see this?
Bob Z.
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Sounds like a ZIT!!!!!!!!!!!!
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I sometimes see bubbles after a plane has been in service for a few years. A friend of mine said it is most likely due to fuel/oil eventually getting thru the dope since dope is not fuel proof. After a while, this penetration produces the bubbles. I have no way of knowing for sure if this is true.
Another cause might be the dope adhesion. I think the products we use today are not as good as they once were, probably due to EPA regulations forcing manufacturers to change things to lessen toxicity.
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Bursting one of the bubbles made made the white stuff squeeze out like toothpaste - as I said, MESSY.
The finish was nothing special - I have been using the same process for many years on at least ten different aircraft.
Brodak clear dope, sanded between coats, a layer of .5 ounce fiberglass cloth doped on, a few more coats of clear, then color and finally a few coats of clear, all sprayed on.
I have seen stuff like that before, but not enough to bubble. It's fuel getting under the clear and into either the color or fillercoat. Some batches of Brodak dope aren't remotely fuel-resistant and are easily dissolved, even by exhaust, much less raw fuel. Once it gets enough of it under the surface, it can dissolve the paint and then get trapped, making a sludge. If it gets sticky from oil or fuel on the outside, it gets wipted or scraped off, underneath it just gets trapped. In this case, maybe the clear is from a batch with some resistance and the fillerrcoat was made with a different batch that is not.
That's why I don't even like using non-fuel proof materials underneath nearly bulletproof urethane or epoxy, any small nick in the wrong place and it can undermine the finish. People who use dope are obsessive about keeping fuel off it it and wiping up any spills or exhaust ASAP.
Brett
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Thanks for the advice, Guys.
Yes, I tend to agree that it's fuel related but why such a pure white?
I did coat the entire fuel tank compartment with two coats of Finish Coat Epoxy but either I missed something or a crack opened up.
I peeled some of the paint off the fillets and they were a bit soggy but not white.
Oh well, I'll just patch it and fly it a bit more.
It's really a joy to fly - I may build another.
Bob Z.
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Good point, Ty - THANKS!
Bob Z.