Removing rust without harming paint
 

I picked up a late 80s Bianchi yesterday with a LOT of chips and scrapes in the paint, many of them containing little spots of rust. I've read about rust converters and oxalic acid for removing rust, but it's not clear to me if these will harm paint and are only meant for stripped frames.

Is there a product I can use to kill the bits of rust without harming the surrounding paint?

Thanks!

if the paint has any durability, a #00 fine steel wool scouring pad and WD-40 or similar will get rid of the rusty spots. if the rust has crept under the paint, then the paint there will chip anyways.

Thanks. I'm probably going to disassemble the frame and take a close look at it today, and I'll try your suggestion. If things look really bad, I'll probably just get the frame powdercoated.

Oxalic acid will eat up good metal just as quickly as rust. You want to use Naval jelly, which removes rust and stops at good metal. Safe on paint as well.

I think you would need to leave the part in the Oxalic acid for quite a while to have a loss of good metal. I and many BF members have had great results with it. Dilute solution and a few hours in the bath and then a gentle 'srcub' with a white Scott's pad and finally a quick rinse in the baking soda bucket to neutralize that acid. Dry and apply wax and or frame saver (if doing a frame) and you are complete.

I have had parts that looked like something from a scrap hauler's truck come out looking respectable to very good with it.

Oxalic acid seems to be in fashion on many of the bicycle boards but Evapo Rust is a far superior product for removing rust without risk to the existing paint. Harbor Freight sells Evapo Rust for about $20 per gallon and it has no dwell time restrictions like Oxalic acid does.

The problem is I'd mostly be treating little chipped/nicked spots on the frame that are surrounded by good paint that I want to keep. It doesn't sound like Oxalic is safe for the surrounding paint, and I could'nt really soak just one spot on the frame.

I had looked at naval jelly, but I can't find anything definite that says it's safe for surrounding paint.

Like Oxalic acid though, I'd have to find a way to soak effected region of my frame - and I'm not really sure how to do it, logistically. Any ideas how I might treat just a few small areas on my top tube, for example?

Well, both navel-jelly and oxalic acid will cause problems with the paint. That's because they will creep sideways under the paint and work on the rusty metal underneath the paint, resulting in loss of adhesion. Or in the case of oxalic acid, just metai will do. In either case, you want to tape off the paint and leave just the rusted spots exposed.

The problem with this kind of rust is that it's pervasive and rust in anaerobic conditions (under paint) will actually spread faster than exposed rust. Most likely in your case, it'd be best to strip the entire frame, remove all the rust with naval-jelly, sand, primer, sand some more and paint.

see here: http://www.bikeforums.net/classic-vi...l#post19348848

While I normally try not to participate in resurrected zombie threads, I'll throw two cents into the conversation here for posterity's sake...

I've used a weak oxalic acid bath on multiple frames, forks, and components. It's never damaged any paint or decals on my bikes and does a fantastic job removing rust. The only thing I've damaged using oxalic acid is the black oxide finish on a headset race. Further research after that incident confirms that oxalic acid isn't safe for black oxide coatings on steel, such as you'd find on allen wrenches.

I've also had good experience using Evapo-Rust and I regularly use the stuff for small parts, but it's significantly more expensive and may be cost-prohibitive for big items like frames & forks.