Originally Posted by
Fumbles22
1). Do I need to get rid of the rust before I coat it in touch up paint? I don't want to sand it since it could damage the paint around it.
Yes. If you paint over rust, you'll have a mess within a year. You need to remove as much of the rust as you can by sanding. Do this carefully to minimize damage to the surrounding paint. One trick I use is to wrap the sandpaper around the "point" of a 1" x 2" pink pencil eraser. That provides a nice point for sanding in the scratch. If you do it right you will also feather the edges of the existing paint which you want to do anyway before applying the touch-up. After sanding, treat the spot with a rust "converter" (you can find a variety of brands at the auto parts store). This will chemically seal the surface and hopefully prevent new rust from forming under the touch-up.
2). Do I have to lacquer over it? Some touch up paint doesn't seem to require lacquer, but should I lacquer over it anyway?
By "lacquer" I think you're referring to the clear coat (which may or may not actually be lacquer-based). Automotive touch-up paint is generally a lacquer formulation and will have good gloss without the need to apply a clear over it.
3). How do I deal with scratches to the lacquer, but not the paint?
If they're really noticeable, sand them down until you hit the color coat (try not to sand to bare metal) and touch-up normally. You can get clear-coat touch-up paint, but it's really hard to get good results with it.
Note that the key to touch-up painting is what you do
after applying the paint. You will generally need to apply several coats of touch-up to each chip and scratch in order to "build up" above the level of the original paint surface. The result will be a lumpy ugly blob that looks almost as bad as the chip/scratch. Now you need to grab a sanding block an some wet-dry sandpaper and wet sand the spots to smooth them out and bring them flush with the original finish. Start with 800 grit and work down to 2000 grit as the spot starts to blend with the original paint. Lastly, hit the now dull but smooth spot with some polishing compound to bring back the gloss.
As you can imagine, this process is a lot of work, so unless this is a rare or vintage frame where you're trying hard to preserve the original paint, disassemble and take the frame to your nearest powder coater to have it sandblasted and powder coated. Cost will likely be under $200 and you'll save yourself at least 8 to 10 hours of labor vs. doing high-quality touch-up work.