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Building Tips and technical articles. => Paint and finishing => Topic started by: Warren Wagner on December 12, 2009, 04:35:07 PM
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Gang,
My, what was once, a nice finish is beginning to break down. Certain failure modes I can understand, but this one is very strange. Why would a finish start to lift with this peculiar pattern???
It is obviously an adherence problem, but rather than lifting off in a sheet, it creates this crazy geometric pattern that keep repeating and repeating.
The finish is Rust-oleum over a dope base, and has lasted roughly 8 years before this began. I have my *theory* as to what is happening, but I won't mention it so as to not influence your thoughts.
Refinishing a plane is waaaay down on my list of things that I enjoy doing.
TIA
Cheers.
Warren Wagner
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Best guess,
there is some form of solvent swelling going on. typically you will see this sort of pattern when solvent is introduced to cured paint. As in wiping it with some form of solvent, which then swells the cured finish and it cannot absorb the solvent so it puckers.
Normally this would be say, enamel, with laquer put on it,
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Its called 'gatoring' or 'alligatoring' (looks like...). As mentioned, it's from the paint getting hit by solvent that weakens the bond to the paint underneath and swells it.
High-nitro fuel gators dope like nothing else I've seen, BTW.
On a new finish with catalysed paint it's caused by painting over a layer that's not fully cured (my unfortunate familiarity with it comes from spraying gel coat for fiberglass parts -- get it too thick and it peels off the mold before the part gets made; get it too thin and it never sets entirely, then it gets attacked by the solvents in the fiberglass that's applied over it and it gators).
I'm not entirely sure why it'd happen to and old finish, but I suspect it's a combination of an insufficient bond to the underlying finish and an unfortunate accident with some sort of solvent.
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I also agree with Mark. Remember, there is no chemical bond between Rustoleum (enamel) and dope. just the mechanical bond. so if any solvent or oil or whatever causes the enamel over the top to swell, there is no chemical bond underneath to hold it together.
Something similar happen to a classic plane I had that what upside down in a work rack. The fuel line burst and all kinds of fuel pored into the engine compartment (and through the vents to run down the topblock). I didn't realize it had gone to the top of the plane and it sat like that for about 10 minutes. When I flipped it over, it looked just like this all the way down the nose. The plane was dope from the wood up with catalysed polyurethane topcoat. Same problem. There is not much chemical bond between dope and urethane so there wasn't enough adhesion to hold things together. Took a lot of cleaning and sanding, but it was eventually fixed (shame the plane very flew worth spit - it was a pretty thing).
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I had a very similar problem with a finish done with Pactra Formula U spray cans. It seemed to me that it was the oil in the fuel that was causing the problem. Anywhere where oil collected showed that effect.
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Actually, those are alien runes. They are trying to communicate with you the only way they know how! Beware of being in open spaces without your head covered in aluminum foil!!! LL~