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Oxalic Acid

Old 09-24-23, 11:11 AM
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Oxalic Acid

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

TIA
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Old 09-24-23, 12:32 PM
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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.
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Old 09-24-23, 12:50 PM
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I go much more dilute: 1/4 cup / 5 gal, or, 1tbs / gal
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Old 09-24-23, 01:20 PM
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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.
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Old 09-24-23, 01:30 PM
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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.
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Old 09-24-23, 01:51 PM
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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.
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Old 09-24-23, 02:12 PM
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Originally Posted by oneclick
Putting two different metals in an electrolyte bath is a recipe for corrosion.
Yep, basics of plating.
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Old 09-24-23, 03:15 PM
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There was a whole thread for guidance on oxalic acid, I guess buried now.
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Old 09-24-23, 05:31 PM
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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
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Old 09-24-23, 05:37 PM
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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."
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Old 09-24-23, 07:27 PM
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Originally Posted by SurferRosa
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.
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Old 09-24-23, 08:30 PM
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I cheat and go the easy way - I use the stuff that goes by the brand name "EvapoRust." Straight out of the jug.
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Old 09-26-23, 04:28 AM
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Originally Posted by mrv
I got a gallon of green stuff from Lowe's
That's Phosphoric acid.
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Old 09-26-23, 05:42 AM
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Originally Posted by bark_eater
That's Phosphoric acid.
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)?

Last edited by mrv; 09-26-23 at 07:21 AM.
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Old 09-26-23, 06:18 AM
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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.
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Old 09-26-23, 07:44 AM
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Originally Posted by 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)?
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.
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Old 09-26-23, 09:06 AM
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Originally Posted by 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.
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!"

Last edited by mrv; 09-26-23 at 09:42 AM.
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Old 09-26-23, 09:11 AM
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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.)

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Old 09-26-23, 10:57 AM
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Should wash with baking soda solution to neutralize the oxalic bath when done.
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Old 01-29-24, 09:39 AM
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I've been reading some (of many!) topics on OA, and I am starting on making my soaking tub.

(a) A friend sent me a link to some safety warnings on using the product, what do y'all use to be safe? I guess a pair of regular safety glasses and disposable gloves just might not suffice.

(b) Doing three frames (on is a 25", I'll build the tank to fit that as I doubt I'll every do any bikes bigger), two are scuffed up but I intend to save the paint; the third I've had soda blasted. Any reason I cannot soak all three, including the bare one? It's really bare, but I want to clear out the inside of the tubes.

(c) Is the chemical action temperature-affected? I was thinking about doing this in my basement, but wonder about fumes. I do have an enclosed porch and can open it up for a lot of ventilation -- but it's winter. Will cold temps slow/stop the process? I recall stripping the paint from my antique car in an unheated garage, almost nothing was happening until it warmed up, and then the difference was amazing.
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Old 01-29-24, 11:08 AM
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I posted here (in 2009!) about a rusted chromed Raleigh International. I don't remember details now, but I used the very weak oxalic acid method. Something like a few tablespoons in 3+ gallons of water? Soaked for hours. Nothing seems to happen at first, just wait a bit.
The whole thread is useful.

I couldn't fit the whole frame in the plastic box, but the rust was at the headset and rear dropouts. So those got treated separately.

At that weak concentration, I didn't take many precautions. No fumes, no adverse skin effects (but I quickly rinsed my hands if they got solution on them.)

It's quite amazing how the rust disappears. But a few years later, with the bike in storage inside my house, rust was reappearing. I didn't do anything to seal the spots where the rust was.

before






After

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Old 01-29-24, 11:50 AM
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I foolishly don’t take any precautions other than putting a top on my OA bath tub in case the dogs get into the garage. I put a whole box of wood bleach in my tub with enough water to cover the frame and fork, let it soak 24 hours or so, rinse it off real good, and put a box of arm and Hammer in the tub before I dump most of it down the drain and the rest in the street. WRT paint and decals…it depends.
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Old 01-29-24, 05:47 PM
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Chemical reactions are invariably temperature-sensitive. Simple ones like oxalic acid for rust speed up with increases in temperature, slow down as temps fall. More complex reactions like aluminum dissolving in sodium hydroxide (lye) generate heat so can get out of control rather quickly depending on surface area and solution concentration.

In relatively weak solution oxalic acid is fairly safe on exposed skin, it's your eyes you want to be careful of. Splashing acid will quickly damage your eyes. Best in any case to rinse spillage with plain water if on your body, neutralize with baking soda & water elsewhere.

Citric acid's a good substitute, works almost as well if not quite as fast in water solution. I use a product called LemiShine if I can find it. Be aware there are several products under that brand name that have different recommended uses hence different chemical composition. The one I like is this one; I use maybe 1 or 2 teaspoons in a quart of water but my batches are pretty small compared to what it'd take to do a bike frame. With something that size I'd think maybe quarter to half a cup in 5 gallons'd be about right.
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Old 01-29-24, 06:56 PM
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+1 to the post above. I'll just add that I've used Oxalic multiple times and taken few precautions. That does sound dumb but I don't consider it a very hazardous substance. On the other hand, using lye to dissolve a stuck stem or something I take very seriously.
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Old 01-29-24, 07:04 PM
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Barkeepers Friend works well on small areas of rust on frames. I beleive it contains OA.
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