In the "Minwax Poly What?" topic, Phil said "Don't use water-based urethane on silkspan over open bays.  It will get brittle as hell.  Works fine over wood and foam though..."

I would like to find a fuelproof paint type that can be used over heat-shrunk polyspan on open bays from the ground up for a completely dope-free finish.  Either water-based or solvent-based.  Does anyone know if such a paint exists?

Thanks.

You can also use automotive urethane (both catalyzed and non-catalyzed). As long as you aren't looking for shrinking.

A few years ago I experimented quite a bit with various finishing systems. I would love to use all auto urethane finish (with catalyzed primer) but the key element was that urethane doesn't shrink at all. So it was either build a plane without open bays (all sheet construction) or keep using lacquer for at least open bays. I tried several combinations but the truth is, the incompatibility issues make this difficult; particularly if repairs or alterations were needed.

I finally gave up and went back to good, old dope (butyrate lacquer). So now I use lacquer from wood up through color then use catalyzed polyurethane for a top coat. I just works the best for me. But if I ever do a plan that doesn't have open bays (maybe a foam wing or something), I will consider going back to urethane.