So I posed this question in the Bike mechanic forum too, but was recommended to ask it here by the SS/FG forum.

I have an old early 70's peugeot UO-8 that I am restoring, and It has some minor rust here and there on the frame.

A guy I know who restores old frames suggested that I use some oxalic acid. He had said to dissolve a bit into some warm water, soak some paper towel in it, and then wrap the paper towel around the rusted parts, let soak for a bit, and then wipe off.

Well I tried that, and while it did help remove SOME of the rust, it didn't remove that much. He said that sometimes, if it is being difficult, I could make a concetrated paste out the OA, and maybe even add some Zud or Barkeepers to it, then scrub the rust with something that won't scratch the paint.

Which is what I am planning to to next, then I have some rustoleum stops rust protective primer to put on once I have removed the rust.

The question I have is, is the paste method the optimal way to remove the tougher rust from the frame? Is there a better way?

I don't want to re-paint the whole frame, my plan was remove the rust, apply some rustoleum primer, then just do some paint touch ups, so I don't have to remove the decals.

If you are just touching up some spots, I would use a rust converter primer instead. I am a huge fan of oxalic, I have a fork and several parts soaking right now. But I use the rust converter if I am just going to touch up a few spots. Note, whether you use the oxalic or the rust converter, the rust needs to be exposed. So if you have rust under the paint in spots, you will need to expose it. I carefully use a dremel for that task.

I was going to use a Rust converter, which I have, but the frame is white, and all the rust converters I have seen turn to black, not a HUGE deal, but still.

I thought you were touch up painting it? I use rust converter even after oxalic, as a final "kill" of any remaining rust, as a preventive measure. I never go straight to touch up paint.

Let me add that you should not mix oxalic acid to a "paste" consistency, that would be way too concentrated!

try naval jelly (same thing). follow the instructions and don't leave it on too long. rub hard with a rag when removing it. repeat as necessary. follow it up with some clear nail polish or something else.

It is impossible to mix oxalic acid to a paste. It is, however, quite easy to make a paste of Zud Cream Cleanser, Zud Powder Cleanser and OA if you need something to cling to a small section.

BTW, illwafer, Naval Jelly is phosphoric acid, not oxalic acid. Not the same thing.