Steel Charlie

So tell me how strong this stuff can be mixed before it starts lifting decals and paint?
And does it derust chrome?

TIA
Charlie

abdon 

It derusts chrome well.

1 gallon to a pound of oxalic acid works well. Honestly half of that works well. This is what I use to derust bare cast iron car parts so unless your bike looks like that I would not go any stronger and in fact would go half.

$h1t will start going south not on the strength of your solution but on leaving it there longer than it needs to. Soak it, gloves and a rag to work it in, then take it out and wash it. You can leave the parts soaking overnight but then again that's what can hurt the stickers.

Watch out for bronze and copper, it will clean them well but if left overnight a nasty film will build up on everything else.

nlerner

I go much more dilute: 1/4 cup / 5 gal, or, 1tbs / gal

abdon 

My mix is for a perma-batch of oxalic acid I keep in a tote to dunk things as needed; dunk, clean, dunk, clean, repeat as needed. For overnight soaks you can indeed go 1/2 cup to a gallon.

He did ask how strong he could go. I would not go more than pound to gallon strength. It would not convert the rust any faster.

albrt 

In my experience it works super well with chrome, especially with small chrome bits that are otherwise hard to get cleaned up. This is with a fairly weak solution, less than a tablespoon to a gallon.

The problems come when you have an assembly with different types of surfaces, the OA will act very differently. For example, if you have an old wheel with chrome rims and galvanized spokes, the amount of time that you need to leave it in there to get the rust off the chrome will be too much for the spokes, and it will leave a crusty buildup.

oneclick 

Putting two different metals in an electrolyte bath is a recipe for corrosion.

If I can't get the steel by itself, it doesn't go in the bath.

spclark 

Yep, basics of plating.

repechage

There was a whole thread for guidance on oxalic acid, I guess buried now.

SurferRosa

A search on thread title ("oxalic") results in 81 threads in C&V alone, like these:

Oxalic acid is chromes best friend

My Oxalic Acid OA Bathtub

The wonders of Oxalic Acid...

WARNING on Oxalic Acid - READ

Oxalic Acid questions

albrt 

Oxalic acid is cool stuff. I was amazed the first time I put a bunch of rusty chrome Schwinn parts in a bucket and they came out looking brand new.

But as the editorial page writers used to say about pretty much everything, "it is not a panacea."

mrv 

I think one of these threads argued for a 5% solution. I got a gallon of green stuff from Lowe's , which I figured out was a 50% solution, so I diluted appropriately using the metric system.... which is easier than oz, gal, qts, or whatever.
I soaked the Allez Castrophe' ( https://www.bikeforums.net/g/album/28780430 ) overnight after paint strip. As far as I can tell.... it didn't hurt!
But the frame was in a REALLY bad way when I got it: missing cable guide, corroded cable guides; fused stuck quill stem.
I'll see if I have any better pics to add to the album after soak. It's painted now, but not clear coated yet.

I also used an undiluted solution to short term soak (~45 minutes?) another frame. that was in bad shape (fused seatpost; incredibly stuck BB, big ding in the DT). This cheap Fix8 project I'm still working: https://www.bikeforums.net/g/album/30495164
-- I'll load more pics shortly. It's no painted Spray.Bike "Ag". Really kind of looks like the Tin Man....

Anyway, I am really hoping the oxalic acid inside the frame helps convert any unseen corrosion. I'll treat the inside of the tubes with something - FrameSaver if I can get it, otherwise PB Blaster or boiled linseed oil.

cheeers.

bikingshearer 

I cheat and go the easy way - I use the stuff that goes by the brand name "EvapoRust." Straight out of the jug.

bark_eater 

That's Phosphoric acid.

mrv 

labeled as "Concrete & Metal Prep" : https://www.lowes.com/pd/Klean-Strip...GAL/1001456348
- the flavor of acid is not on the label. I saw many variations of deck cleaner sold in very large quantities, which also did not state what kind of acid (going by memory)
- I believe I picked up the Klean Strip since it is labeled "metal prep", and came in a smaller quantity, and basically shelved in the same location.

you are correct, the MSDS states 10 ~ 30% Phosphoric acid: https://www.google.com/url?sa=t&rct=...7&opi=89978449 (directs to PDF, i think)


hmmmm..... - I guess I didn't really need to dilute it!! https://www.practicalmachinist.com/f...emoval.210082/

Any thoughts from the pros on Oxalic vs. Phosphoric treatment? Does Oxalic REMOVE rust, where Phosphoric converts rust to iron phosphate (a black coating)?

SJX426 

I don't recall the ratio used but here is before and after pictures. Did this back in 2009.
Colnago Fork Crown as bought on Flickr
P9161264 on Flickr

Bought the Oxalic as granules in a small container at the paint store, Sherman Williams IIRC. Still have some left. For the fork, I used a wallpaper soaking tray. I also built a 2x8 frame joined with hinges as a tube using in black Visqueen as the liner. The hinges allowed me to soak different size frames.. Use cinder block or something else in the spaces of the frame to minimize the amount of fluid. Let it soak overnight. No damage to paint or decals. The missing paint on the fork was from another mishap by a PO.

If the solution is too strong for the amount of time soaked, it will leave a white residue.

bark_eater 

I've used this a bit. Its pretty good good for derusting junkers with out disassembly. I brush Penatrol on after. I need to get the dilution and neutralization right, as I sometimes get a white "corrosion" with exposure to the elements.

mrv 

When I pulled my fully stripped of paint Allez out of the ~5% solution overnight soak (now I know it was phosphoric soak!), it was very dull gray. I didn't have any white residue.
The shorter soak (and scrub) on the very cheap and not completely stripped made in China Fix8 didn't seem to matter.
Doing some short searches, to distract me from working...., I'm not sure what the white residue is - either from oxalic or phosphoric - someone on the internets indicated some kind of salts. Which may be why it needs to be removed before painting.

i need to post pics of my frames post paint - - as cautionary tails. Like I always told my kids when they caught me doing the wrong thing: "Even a bad example teaches a good lesson!"

spclark 

Phosphoric acid leaves phosphate (salt) behind. With iron alloys (steels being a large proportion) that phosphate's mostly insoluble in water.

Oxalic acid leaves oxalate (salt) behind in similar usage; oxalate is water-soluble hence easily washed away leaving bare metal.

(I remember enuf chemistry from school to be dangerous, why I tend to learn as much as I can when I'm in doubt about something. Been coming here a lot since I discovered these Forae.)

SJX426 

Should wash with baking soda solution to neutralize the oxalic bath when done.