Clint,
Using catalyzed polyurethane top coat is no more difficult than using dope. The process is different. It's not easier or harder, just different in process. With dope, you have to lay on clear in stages giving it enough time to dry well before the next coat so that the coat underneath doesn't blend with the one you just shot on. The idea is to build up layers. Takes maybe 6-10 coats of clear to get a really good top coat with dope. Lacquer is fairly forgiving in that if it blushes or messes up in some way, it's not all that hard to fix and just move on. After it's dry enough (several weeks at least), it's pretty easy to sand and buff up and you can get some really nice finishes with it, albeit high maintenance ones.
Catalyzed Polyurethane is actually pretty easy to apply. It does best in moderate temperatures. When I can shoot it in a 60-80 degree temp range, it very easy. Just mix the base and catalyst and shoot it. A light "dust" coat, let it dry for maybe 10-15 minutes, then blast a nice medium coat over the whole thing and you're done. Let it dry for 24-48 hours and sand it out and buff it up. Give a lustrous finish.
When the temp is under 60 degree, you have to mess with it a bit. I've shot it in temps down to 45 degrees, but it requires some reducer to get it to flow and not orange peel. Above 80 degrees and you really need to use a slow catalyst, but it's not all that hard to figure out. And the best part is, it's largely fuel proof (unless you rub it too thing like I did on the Shoestring - heck of a way to find out).
The Cobra I repainted is all dope through the top coat. It worked fine also. Your choice. The polyurethane in much more fuel resistant so you don't have to be as careful with fuel. Dope is durable in other ways and works fine.
A note on repairs: It's true that the process of repair if the plane is damaged is complicated by the use of catalyzed polyurethane as a top coat. But it isn't hard once you know the process. When I fixed the Shoestring, I just had to sand the polyurethane back so it is outside the repair area. Fix the problem, re-shoot the colors, then re-shoot the clear. There are some tricks to getting it to blend, but they aren't hard once you've done them. Even after the repair, I got 19 points for the Shoestring at the NW Regionals, so obviously it's possible to fix so that the repair is largely undetectable (glad it's wasn't too sunny during appearance judging -
)
If you decide to use polyurethane for a top coat, you'll have plenty of help here. If you go with dope, well, you still have plenty of help if you need it.
A note on test panels: I use old gallon dope cans and fuel cans (well cleaned) for test panels. Mark is exactly right (as usual). Just shoot some primer and go to it. Wish I would have done a test panel before I shot the Novi. I would have know that the florescent lime green (supposed to be candy green) is hard to tone down.
Topic: Playboy build pics II (Read 3899 times)
