This isn't a bike mechanics question per se, but it seems close enough. I'm getting a custom vintage-style frame made and I want it unpainted with a clear powder coat only. I got an unrelated email yesterday from Darrell of Llewellyn Bikes saying that "clear coat only = rust (always)."

He was referring to clear-coated lugged stems, but does that also apply to clear powder coating over a bike? Maybe just to liquid clear coat? I obviously don't want an expensive custom frame rusting...can anybody offer expertise?

While I can't give experience from long term results...my Dad stripped his old Stumpjumper frame down to bare metal and had it powdercoated. It looks great and no rust so far.

Apparently this is a very popular style with hotrodders to show off their bodywork skills. You may find more info on the long-term results in that arena.

You might have a chance with powder coat but I wouldn't expect it to last as long as a pigmented coating.

My understanding is that some techniques for using clear coat only will eventually result in rusty looking patches and kind of blotchiness than some people would find unappealing. As I recall, this is only an aesthetic problem.

I think it is only logical that if a pigmented paint prevents rust, then a chemically similar or identical method of applying a clearcoat would also prevent rust... perhaps clearcoat is designed to adhere to other paints and the pigmented paint is designed to adhere to the base material... and paint peeling off a clearcoat-only bike is harder to notice and touch-up.

Clearcoat can simply be a pigment-paint without the pigments. However, the binder-base is typically not perfectly clear; they tend to be yellowish in color. A clearcoat that's perfectly transparent isn't the same stuff as the regular paint without pigment. And it's far from being similar to primer with its bare-metal adhesion and corrosion resistance as well.

There's also a wide variation in powercoating materials as well. Best to consult with your paint-shop before doing the work and see what they recommend and what kind of guarantees they'll provide.