sekaijin

Kurt was kind enough to send me this magnificently rusty fender for my AMF Hercules resto.



It was the guinea pig for my first oxalic acid soak.

Before:



After:



So, the good news: the surface rust is gone. The only rust left is where it eats all the way through the paint.

The bad news: the box striping is also gone. Also, there's a cloudy whitish patina. Any suggestions for getting rid of that?

bigbossman 

Spray with WD-40 and wipe down.

BlankCrows

What was your mixture recipe? You can get that other rust off too. Soak it again.

phoebeisis

Just curious, is Oxalic acid "better" in some way than citric acid? I've used citric acid to revive bike and motorcycle parts that were Katrinaed-worked ok, not toxic but will burn your eyes(a lot) and skin(a little),so be careful.
Charlie

stausty

Oxalic acid is superior to other acids for rust removal because it forms complexes with iron ions much better. The oxalic acid can pull the oxidized iron out of the rust and into solution where it can be washed away. Anyone who has seen a pale green color in the oxalic acid bath after soaking parts for a while has seen the iron-oxalate complex ([Fe(III)(C_2O_4)_3]^{3+}) in solution. Other chemicals will do this, including acetic and citric acids, but because of its structure oxalic acid is the optimal choice.

Yes, I'm a chemist.

southpawboston

i suspect the whitish patina may be residual oxalic acid binding to the paint and/or metal. i find this happens when i use higher concentrations of oxalic acid. i would try to scrub it off with steel wool and lots of dish soap and water. to remove all the rust effectively, you would need to strip the paint off so that you can get the rust bubbles that have formed underneath the paint.

sekaijin

I'll try that ... that was my hunch, but I wanted to post the query first.

I used Savogran wood bleach from Sherwin-Williams, as recommended on BF.

What recipe? Very scientific: I added a little and soaked it overnight, it barely removed any rust, so I added a little more and left it another 24 hours. I was nervous about using too much. If it won't (further) damage the finish, I can try soaking it some more.

Concerned that steel wool would (further) degrade the paint finish - when I've used steel wool for spot work on paint, it dulled the finish.

Not gonna strip it ... but yes, it is bumpy from rust bubbles under the paint.

RobbieTunes

OA works great.
Heck of a buzz.
The aftertaste, though, I could do without.

southpawboston

depends on whether you're trying to preserve the paint finish or not. if you're concerned about preserving the finish, steel wool is bad. but if the finish is too far damaged to salvage because of severe rust bubbles (as the fender pic suggests), then stripping completely with steel wool and oxalic acid works great. obviously, this would require a repaint afterward.

Karloman

What do you think of phosphoric acid ?

cudak888 

Glad to see you're having fun with that fender there

I'm staying tuned to the thread.

-Kurt

stausty

From Wikipedia, phosphoric acid does form a soluble compound with the oxidized iron in rust, but something not as soluble as oxalic acid. It also leaves a gray film on the outside of the piece while oxalic acid leaves the metal bare and clean. Phosphoric acid is cheaper and less toxic, though.

jacksbike

OK, I see many posts about oxalic acid. I asked my local hardware store about it, and they had not heard of it. Where can I purchase some ? Seems that it is sold dry in a bag, and you add water ? I am always working on some rusty bike parts, and would like to try this stuff out. Thanks in advance for any information.

jebensch

the OA reacts only with the exposed metal/oxidized surfaces while leaving paint and clearcoat unblemished? I haven't tried this yet but I've got a gnarly inner BB shell staring at me and wondering if this is the medicine.

bionnaki

...and how do you dispose of spent oxalic acid? I hope it doesnt end up down the down or into the ground.

beech333

wood bleach. People use it on decks. The hardware store really should have it.

Karloman

But as a deruster is it as efficient as oxalic acid ?
And for both of them, in the long term isn't there any side effect to fear like corrosion starting again ?

Thanks for your expert replies !

extraboldroast

just a repeat of what you've heard before. i was having trouble finding it, so i searched for all tru-value hardware stores near me, and started calling. i just asked if they carried "wood bleach in a tub, that i can mix with water." the first didn't have it, the second did. when i got there to pick it up, i told the manager i had a tough time finding this stuff, he shrugged and said "oh? we *always* have it."

from my experience, around here sherwin williams does NOT carry this stuff (called and went there), lowes and home depot thought i was crazy, said they had never heard of such a thing.

sekaijin

^^ Sherwin-Williams sells the wood bleach under the Savogran brand. At my local Sherwin-Williams they gave me blank stares when I asked for it. I persisted and eventually they found a tub of it hidden somewhere covered with dust. Not a fast moving SKU for them.

I will have a rusty fender update later. When the bike's other parts are ready for their OA soaking, the fender will get its second round.

Question: it is bad to soak something in OA longer than it needs? I have parts ranging from light to heavy rust. I'd like to soak them all in one OA bath. Will a longer stronger OA bath be harmful to the barely rusty pieces?

sekaijin

Update: 2nd OA soak of Kurt's rusty fender in progress.

Here are a few teaser "before" pics of other parts in the tub:











"After" pics to come ...

Primitive Don

check Ace Hardware if they have those near you

wtgrantham

you can find OA on ebay at a reasonable price. I bought a 5# bag. Just search "Oxalic acid"

chrispe

wrk101 I have 2 questions. First did you unspoke and then respoke the wheel when you did this, and second did you soak the whole frame in it and if so what did you do this in. I was considering soaking a whole frame at some point, but have no experience with this and was wondering if a shallow plastic kiddy pool would work.

Karloman

Hey sekaijin, where are those pictures you promised us ;-) !

tarmenel

Take a look here, might be what you're looking for https://forestbikes.blogspot.com/2010...op-update.html