Tell Me About Oxalic Acid

[mbstude]

First, apologies if this is in the wrong section.

I just bought a really dirty "40-years-in-a-barn" 49 Schwinn. The paint looks great under all the grime, but there is some surface rust staining and most of the chrome has a rust coating.

I've seen oxalic acid mentioned here but I couldn't find an explanation of the process in a search.

I see that I can buy powder and crystals online cheaply enough. But, what do I do with it?

If someone could fill me in with instructions on what works for them, I'd appreciate it.

Thanks!

 

[Greg M]

Here you go, just scale up for a full frame:

 

[GTs58]

Wow, over a pound of OA in maybe a gallon of water! I call that extreme and way off the ratio chart that it doesn't even compute.

This should be in the restoration tips section. Lots of info on OA there.

 

[mbstude]

Thanks for the video link. So, it looks like it's a simple as mixing the powder with water and letting the parts soak.. Cool.

Is it safe for painted surfaces?

 

[rickyd]

As mentioned above tons on OA in Restoration section. Also smarter folks than me mention red paint may turn brown.

 

[SirMike1983]

Thanks for the video link. So, it looks like it's a simple as mixing the powder with water and letting the parts soak.. Cool.

Is it safe for painted surfaces?

http://thecabe.com/forum/threads/rust-on-paint.67574/#post-606988

The short answer is "maybe" on paint. Certain types of paint and certain transfers will not respond well to it and may come off or change color. Other types of paint respond very well. Red paints tend to be more suspect, especially those where the paint pigment uses a rust-derivative to get the red color.

The acid crystals to water ratio vary from person-to-person.

http://thecabe.com/forum/threads/oxalic-dip-question.80570/

Removing rust with 0000 steel wool and WD-40 is not as thorough, but may yield a more consistent result across the paint. Oxalic will get into the little spots of rust much better, but also cause the bare spots to become more prominent.

 

[the tinker]

Do not use Oxalic Acid on chrome. Read the many posts in the restoration thread about rust removal from chrome.
Much better and safer and easier to use products available. If you only have a light coating of rust on your chrome parts a decent chrome polish will work wonders. Do not use steel wool. If the rust is heavy there are several different brands of rust remover that you can soak your parts in overnight that will remove every speck of rust. Oxalic Acid will not remove grease and grime and dirt. It will leave a tough yellow coating on your chrome that may be just as hard to remove as your rust. Before you grab that steel wool and wire brush remember: your chrome plating is thin and already worn from age. You do not want to remove any more of it.
Oxalic acid gives off very subtle but harmful fumes that are barely noticeable. Only use outdoors.
Yes it is harmful to any paint that uses Iron Oxide in it's pigment. It will turn some, but not all reds pink or a shade lighter.
For the benefit of recent Cabe members that have not thoroughly researched the restoration threads I post these pictures of Oxalic Acid's results on badly rusted fenders soaked over night. These fenders were not cleaned up after soaking for the photo. What you see is photos taken immediately after removing them from the O.X. bath.
Remember that any acid that attacks Iron oxide will seep under the paint and "follow" the rust and may lift paint and chrome that otherwise would have stayed put.

 

[mbstude]

Thanks for the replies, guys. I'm a big fan of Evaporust and I'll use that on small parts, but I'm wanting a more cost effective way to soak larger parts, like bike rims or whole frames if it comes down to it. After a few hours of reading tonight, I ordered a bag of citric acid and will give that a try. The toxicity of the oxalic acid scares me a bit. There's a lot of rusty junk around the shop so it'll be fun to experiment.

Mike, I came across your blog post while searching older threads on here. A very good read! I like the steel wool treatment too. (Btw, how's the blue '48 Continental?)

Tinker, thanks for the pictures and the details. It really brought out the white!

I made a deal for a '49 Schwinn straight bar today that supposedly has spent the last 40 years in a hay loft. It's filthy but even with all the grime, it looks like most of the paint will come to life without soaking. We'll see when it gets here.

 

[SirMike1983]

Thanks for the replies, guys. I'm a big fan of Evaporust and I'll use that on small parts, but I'm wanting a more cost effective way to soak larger parts, like bike rims or whole frames if it comes down to it. After a few hours of reading tonight, I ordered a bag of citric acid and will give that a try. The toxicity of the oxalic acid scares me a bit. There's a lot of rusty junk around the shop so it'll be fun to experiment.

Mike, I came across your blog post while searching older threads on here. A very good read! I like the steel wool treatment too. (Btw, how's the blue '48 Continental?)

Tinker, thanks for the pictures and the details. It really brought out the white!

I made a deal for a '49 Schwinn straight bar today that supposedly has spent the last 40 years in a hay loft. It's filthy but even with all the grime, it looks like most of the paint will come to life without soaking. We'll see when it gets here.

View attachment 361075

If it's all like that, I would not do a large-scale soak. The thing about soaking a whole frame or the like is that you either (a) cannot allow the solution into the tubes, or (b) have to have a way to neutralize the acid in the tubes, then blow out any residual moisture. I'd save a big soak of a whole frame for a worse condition bike.

What may work is a "bandage" set. You soak rags in your acid solution and wrap the tubes in the wet bandages for a certain time. It's a bit less aggressive, so it may work slower.The bandages also allow you to focus on one or two areas at a time.

If it were me, I'd start with a WD40 treatment using 0000 steel wool and a light touch, and see where it goes. You might not even need to use the solution on that.

 

[the tinker]

A word of caution about soaking stuff in Oxalic acid. I am posting this because I have done this with lousy results. I tried the bandage soak. Also the partial soak of only part of an object. { wheels....frame.....fenders }
Submerge the whole frame or fender, wheel whatever or not at all. . If not you will end up with a splotchy looking frame doing the soaked rag thing. Build something the shape of your frame or whatever and line with plastic sheathing to completely submerge your item.When done the Oxalic Acid will be gone after a good washing. It will not continue to "eat" away at the inside of your bike frame. It is not like submerging or applying Muriatic acid to your parts. Granted Oxalic Acid is a toxic chemical and an acid but is more on a par with citric acid [your lime juice] then a something like Muriatic..
It is tempting on a large object like a rim or fender to soak only half of it at a time because of lack of a large enough container. What happens be it because of water temperature,chemical strength , exact matching soak times and the overlap of soaked areas..... or.a combination of all, you will see a difference between the two soaked areas. Gotta soak the whole thing . Sometimes One hour using hot water is enough I have done frames in three hours. Something really badly rusted like those Huffman fenders posted earlier took an overnight bath.
By trying to do half an item at a time there will be a dirty looking "Line" in the paint between the two soaks. And it don't come out.