I'm convinced this topic is covered somewhere, but I've yet to find this exact question in the forums after looking through tons of posts. Just please direct me to the answer if I just didn't find the right post. Question:
I had a framebuilder move my brake braze-ons on an 83 trek 720 (to accept 700c wheels). All in all, pretty cheap and easy - except, perhaps, for the destroyed paint. I know it won't be as good as totally re-powder coating, but what is the best way to paint the 1" area destroyed by the heat?
Tons of threads also deal with actually physically removing or moving braze-ons, which I've already done, or painting an entire bike, which I'd like to avoid.
A lot of threads deal with covering up dings and scrapes, but I don't care about matching the color and it's a much bigger area. For dings and the like, this thread suggests either nail polish, or Testor's model paint, or automotive pens - but I worry the area might be too large. Etching primer is also mentioned. Thoughts?
1. mask off the burnt area with masking tape to prevent damage from spreading too far
2. chip/scrape off any remaining brazing flux
3. sand the area with 200-grit sandpaper and blend in edge with good paint
4. spray with sanding primer (etching-primer only needed on aluminium), let dry completey, use hair-dryer to speed it up
5. remove tape and expand the area slightly so edge of primer and original paint exposed, about 1/8-1/4"
6. sand primer with 400-grit sandpaper, blend edge of primer & original paint
7. spray with paint of choice, I find black easiest to match, otherwise I can mix model-paints to match pretty well
8. remove tape and expand area again by 1/8- 1/4"
9. sand with 600-grit sandpaper to blend in edges
10. spray clear to cover up the repair.
11. remove tape
12. sand edge with 1000-grit sandpaper to blend in
13. polish with polishing compound.
This results in a good-as-new repair. You can skip some steps if you don't need smooth blended edges or perfectly matching paint.
Thanks for the good info; I wouldn't have considered moving the mask to achieve a blend. I am thinking of going the complete opposite direction: as the original color is a sparkly deep brown, a contrasting bright color should be interesting - sort of highlight the change in the bike (and has the added benefit of eliminating color matching anxiety). I also have a heat gun, which can spit out some pretty hot air, so that might be useful.
As far as paint, use sand primer + any kind of spray paint? + a clear coat (I'm guessing ideally of the same brand) - with sanding between each step. I think I got it. I'll make it over to the big box hardware store sometime this week.