Unfortunately, the previous owner did not treat this bike well and the top tube and down tube finish is pretty tattered. The black decal portion is peeling in a spotted fashion. The clear coated/laminated aluminum parts shows spotting - like a clear laminate that has developed holes; not really noticeable form far away, but the holes in the coat traps dirt, so it further outlines the missing laminate areas. There's also lots of minor surface scratches which looks like it's only on the finish.
I'm not looking to repaint the whole bike. I just want to restore the original look as much as possible. But I don't know where to start. Should I strip the decals and the clear coat the top/down tubes (the stays are fine)? And if so, do I use sandpaper? I don't want to further scratch up the frame. The wire brush I use on steel bikes is probably out of the question. And after that, would I just lay down new decals and clear coat, or do I need something for the clear coat to "bite"? Or should I just layer a new decal over the scratched up one?
I've rattle-canned a steel bike before. Though it looks very nice now and the finish has been relatively sturdy, it is more prone to chipping if it gets knocked. Is there a clear coat that's more durable? Is something like clear nail polish better or worse than rattle can clear coats? Or could I use some sort of tape/laminating sheets to cover the bare aluminum?
There is one slightly bigger scratch. Is there a way to fill it so that it blends with the aluminum? What should I use to fill it?
2005 LeMond Reno, old beater Diamondback Outlook - under heavy construction
Not really - in the case of a failed clearcoat you need to take it down to bare metal and start all over again from self-etching primer or epoxy primer.
In your case, the bike is bare, clearcoated aluminum. I'd use a new prep brush for aluminum and call a local auto body supply shop and ask them for Spray Max 2K spray clearcoat - it's a 2-part urethane clearcoat that activates in the can. If you have a spray gun(preferably HVLP) and a stout air compressor to drive it, you can use a automotive clear coat. PPG, DuPont, Glasurit, Sikkens - they'll all work well. Just be sure to WEAR RESPIRATORY PROTECTION, isocyanates are NASTY and TOXIC!