RUST-- Need to be removed?

JudeChow said:

I have some rock chips on my bike that shows signs of light rust..do I need to sand it down then put on touch up paint? I just went over the rust spots with touch up without sanding it down, because I don't want to make the chip any bigger, and touchup paint doesn't really match that well.

I encountered the same thing on my steel frame surly. The shop mechanic told me to carefully sand the rust away (avoiding the surrounding paint as much as possible) and then use fingernail polish as touch up paint. Worked like a charm. My understanding of rust is that it's like cancer. If you don't remove it, it will spread, even under new paint.

JudeChow said:

I have some rock chips on my bike that shows signs of light rust..do I need to sand it down then put on touch up paint? I just went over the rust spots with touch up without sanding it down, because I don't want to make the chip any bigger, and touchup paint doesn't really match that well.

The problem is the rust is very weak and the paint does not stick well to it. It's much better to sand the rust off, then reseal the metal with the touch up paint. Even though the paint does not match, it will protect the metal much better than if you painted over the rust. I suggest you gently scrape with a knife over the touch up paint and you will see how easy it is to scrape off. Then lightly sand the rust off and use the touch up paint on cleaned, bare metal.