Sorry for all these posts on stuff I should have known 30 years ago.
Preface: I've painted a lot of models in my life. For years, I used almost any brand of dope (SIG, Stits, Brodak, Aerogloss, TopFlite Lustrekote (whatever that was). Then I went to auto paint, both two stage and enamel with hardener (I can't use either of those right now, but life is all about learning).
And I always worry about paint being fuel proof, especially with the biplane I'm now building.
But looking at the models on the plane tree last night, something occurred to me: I have never had paint actually soften to the point of smearing and coming off. Not once. And I'm not particularly diligent about wiping planes down.
What I HAVE had happen, especially with some of my fleet that is now more than 20 years old, is the finish lifting off in places, or having bubbles coming up in places particularly around the cowl or forward joints in the fuselage sheeting (never on the wings). Just thinking about it and my best guess is that fuel got underneath the paint or in the wood where the initial coats were applied to the balsa. I will also say, that with the exception of maybe putting a coat of butyrate in the engine bay on occasion or smearing a coat of CA inside the engine compartment on one or maybe two of them, I've never paid particular attention to preventing fuel from soaking into the wood, and I know some of that stuff is going to get past the firewall into the fuselage anyway.
So, I'm thinking that a really good fuel-proof paint or clear coat isn't really going to solve my underlying long-term problem.
On my current build, I'm using (used, I'm starting to sand/primer now) Minwax Polycrylic, which probably isn't fuel proof. So now, I worry about adhesion to wood. The engine bay is still open and I can take some steps to fuel proof it. And I probably need to address the open edges of the balsa when I cut/drill the holes for the needle valve and fuel lines.
Am I crazy about thinking the long-term adhesion is as much, or more, of a problem that the paint itself ?? Well, that was an unfair question, since I'm pretty sure I am crazy.
What steps do you guys follow for protection from the finish lifiting/bubbling ?? I would assume the best way is from step one when applying the first coat of whatever to the raw wood. But it's too late for that.