Anyone Use Oxalic Acid for Derusting

[oliver2-44 9,696]

Anyone else try/use this?

Some time ago an Engineer friend that is an avid cyclist told me about using Oxalic Acid to derust painted and chromed parts on a neglected expensive bike he bought, without damaging the paint or chrome.

I'm always looking for a less labor intensive way to clean and prep parts for painting, and am really interested in the idea of de-rusting but saving the old paint.

This is a mild acid used in products such as Wood Bleach and Barkeeper Friend cleaner.  However anytime Acid is mentioned safety concerns should be learned and heeded.  Thankfully this seems to be fairly mild stuff. 

I finally bought some online from Walmart. (sorry about how this displays)

 

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Florida Laboratories

OXALIC ACID 99.6% Pure, 5 Lbs, Rust Remover, Wood Bleach, Boat Cleaner and More

Average Rating:(5.0)starsout of5stars9 ratings, based on9reviews

10 comments

Florida Laboratories

$18.99$18.99

 

One of the challenges to use it is determining how much of the 99.0% pure acid power to mix with water to use....No instructions on the package. Searching the web I came up with all kinds of answers.  I finally settled on trying 5 tablespoons of acid power to 1 gallon of water.  I mixed up 3 gallons in a five gallon bucket.   I've tried a few pieces of scrap metal and haven't destroyed anything. So I had a slow leak in the front rim on my C160 and found an area under the paint rusted through. I know an E-tank will derust this rim for weld repair/repainting.  But this seemed like a good test for the Oxalic Acid bath. 

 

I'll update this with results!

 

Edited September 21, 2020 by oliver2-44

[SylvanLakeWH 25,493]

[8ntruck 6,991]

21 minutes ago, SylvanLakeWH said:

  Me too.

[ebinmaine 67,309]

5 hours ago, SylvanLakeWH said:

 

5 hours ago, 8ntruck said:

  Me too.

 

Me three...

 

 

Haven't heard of this before. Is there an advantage over an etank?

 

[Achto 27,509]

[953 nut 55,097]

I have used vinegar with about the same results. My go-to rust remover is Ospho or any equivalent Phosphoric Acid metal prep product. I have sprayed it onto rims to remove the rust but retain the patinaed paint, works great.          

[The Tuul Crib 7,336]

E tank is in my opinion The best and safest way to go. Nontoxic you can dump it anywhere when done. And a box of washing soda is merely pennies compared to the harsh chemical.

[WHNJ701 4,165]

Anymore it's what ever your comfortable with and works for you, there are advantages and disadvantages.  Sand blasting isn't an option anymore in my area nobody does it and if they do it's big money. Unless your properly set up it's not safe the breathe that crap in.

I am not a fan of the e tanks either, vinager does the same and your not plugging wires in and filling your shed or house full of hydrogen.  10 gal of vinager is cheap and lasts all season

[ebinmaine 67,309]

22 minutes ago, The Tuul Crib said:

E tank is in my opinion The best and safest way to go. Nontoxic you can dump it anywhere when done. And a box of washing soda is merely pennies compared to the harsh chemical.

 

3 minutes ago, jabelman said:

Anymore it's what ever your comfortable with and works for you, there are advantages and disadvantages.  Sand blasting isn't an option anymore in my area nobody does it and if they do it's big money. Unless your properly set up it's not safe the breathe that crap in.

I am not a fan of the e tanks either, vinager does the same and your not plugging wires in and filling your shed or house full of hydrogen.  10 gal of vinager is cheap and lasts all season

 

 

The off-gassing from an e-tank is one of the reasons I have not set one up yet. 

 

We have a table set up downstairs with a couple of box fans and furnace filters that does a very good job of catching dust.

If it's warm enough we just do all the cleaning outside anyway.

 

 

So if I'm catching this correctly the vinegar does not remove much if any paint?

 

That brings a couple questions to my mind. 

Let's say there's a rust bubble with rust UNDERNEATH paint.

Do you go back and wire brush that manually after?

Also, the paint that's left behind ... is it any good to go over? Do you need to go back and manually remove it as well?

 

[WHNJ701 4,165]

Eric the steps I use:

1. Wash and degrease thoughly

2.  Knock off anything loose with hand wire brush

3. Soak for 2 days, pull parts and hand wire brush, wash parts with water, let dry. Back into the soaker, 2 to 3 days

4. Either parts are done or repeat 3.

 

Most of the time all the paint comes off, I some cases it doesn't.  For this I just spray aviation remover on it to soften it and then back in.

Once the parts are final washed, you need to primer asap, they will flash rust.

Also NO cast parts in the soaker, I don't think it's recommended even for e tank either.

 

My advice buy 2 gallon and try a few small parts and experiment, it will cost you less than 5 bucks

[oliver2-44 9,696]

Here’s some results. I checked it last night after about 4 hours and a lot of the rust in the paint was gone and those spots had a dull silvery black look. But the heavier rust inside the rim was still there

so I left it till this morning so about 12 hour soak. 95% of rust gone, just a few small area left 

But you can see the areas cleaned in 4 hours now have a greenish tinge. 

 @ebinmaine the larger cleaned areas on the bottom face of this rim we’re blistered up paint  So it did soak through. And remove the rust in those area. 

One of the negatives to using this or when I tried Vinegar is the Part will flash rust if not neutralized with baking soda and dried. To me this flash rust less than with vinegar, but will still do it.  A plus is the water on my bucket is not a rusty mess like when using vinegar so the dripping don’t stain everything when removing a part.  As far as safety I finally had to stick my finger, then my hand in it and at the strength I mixed it there was no tingle or reaction. 
Overall  I would say it’s a another tool in the tool box. The 4 hr soak would be a good candidate for saving paint while removing most of the rust and leaving a good surface to wax or clear coat. The 12 hour soak left a good surface to lightly sand and paint color to cover the green tinge.

The E-tank will continue to be my preferred method for complete rust and paint removal. As mentioned above sort of only cost a box of washing soda. But I’ve also killed 2 battery chargers doing it. My E-tank barrel sits outside so I don’t have any concerns with hydrogen build-up.  I recently got a couple of surplus 12v power supplies and will be interested to see how they last. 
Like @953 nut I also like OSPHO for some uses. I actually wiped part of the inside of this rim with OSPHO and it did a good job of preventing any flash rust in that area 

 

This rim will get a weld repair,  then a complete strip in the E-tank. Then a quick trip through the blast cabinet to put a texture  profile on the metal for painting.  After the  welding and grinding.  I’ll do a little JB Weld smoothing around the valve stem hole, then prime and paint. 

[bc.gold 3,403]

I've used oxalic acid to precipitate gold.

 

 

[953 nut 55,097]

11 hours ago, ebinmaine said:

The off-gassing from an e-tank is one of the reasons I have not set one up yet.

I have a piece of 1 1/2" PVC connected to the lid on my E-Tank that is piped out the back wall of my shop. Hydrogen being lighter than air it will just go out by itself. 

[echris 1,425]

Can you guys explain what you mean by etank? Haven't heard of that before.

Also, vinegar... I have a 1954 American Standard oil fired hot water furnace with a potable hot water coil in my house.

When I moved in Nov 2001, that was the first thing I was going to replace come Spring.
That winter, she was running at 85% efficiency. 20 years later, she's still going. Not replacing that old iron. Nope.

The point is, I have very hard water and from time to time the potable hot water coil flow slows badly. Sure you can use muriatic acid, but you need to flush well and it will eventually destroy the coil.
I've been using supermarket white vinegar with an external pump and a 5gal pail to clean it for over 15 years now. 30 mins or so, a flush in between and hot water flows freely.

I kinda love white vinegar. It's like $12 for two furnace flushes. lol
 

[oliver2-44 9,696]

@echris
Google ElectrolisiTank

Anything from a 5 gallon bucket to 55 gallon plastic barrel full of water with washing soda or swimming pool ph+ added to make it mite conductive. You use a 12 volt power supply (old school battery charger)  and sacrificial steel (anode) Connect the charger black to the part submerged in the water container and the red to the scrap metal anode also submerged in the water but not touching the part. Current will flow actually causing a faint circulation in the water. Rust and paint gradually come off the part in 1-2 days. While the scrap metal gets used up  

Edited September 22, 2020 by oliver2-44

[echris 1,425]

Ah, thanks! Electrolysis. I guess I just never heard the term etank before.

EDIT:
Sacrificial anodes - I used to be a boater (old crappy boats) and the sacrificial anodes would eat you out of house and home.

Go on, don't replace them. I double dare you.

Edited September 22, 2020 by echris

[bc.gold 3,403]

3 hours ago, 953 nut said:

I have a piece of 1 1/2" PVC connected to the lid on my E-Tank that is piped out the back wall of my shop. Hydrogen being lighter than air it will just go out by itself. 

 

Not necessarily.

 

Hydrogen embrittlement is a metal's loss of ductility and reduction of load bearing capability due to the absorption of hydrogen atoms or molecules by the metal. The result of hydrogen embrittlement is that components crack and fracture at stresses less than the yield strength of the metal.

 

Full article. Famous failures series: Part 2 – hydrogen embrittlement

 

2. Environmental hydrogen embrittlement
Environmental hydrogen embrittlement can be caused by the external introduction of hydrogen while the bolt or anchor is under stress (Jones, 1996). Such environmental conditions can include (but are not limited to) the salinity of air or water vapour, leachates, admixtures, effluent or acidity of rainwater (Gangloff, 1986).

 

Edited September 22, 2020 by bcgold

[oliver2-44 9,696]

Still doing some testing with this. 
This Suburban plow arm looked completely rusty, no red paint visible. Now after a 2 day soak and a quick bristle brush scrub there’s red paint left. It would oil or clear coat nicely for a patina look. I wetted it and wiped it off to give a quick oiled look

[DennisThornton 4,769]

On 9/21/2020 at 7:26 AM, 953 nut said:

I have used vinegar with about the same results. My go-to rust remover is Ospho or any equivalent Phosphoric Acid metal prep product. I have sprayed it onto rims to remove the rust but retain the patinaed paint, works great.          

What he said. 

 

But the quickest is hydrochloric BUT it's best to use it outside keeping an eye on it's progress AND it will harm good metal if you leave it long enough.  I think any acid will work with the strongest being the fastest and the weakest with the least downsides other than time required.

 

I'm fond of electrolysis and Evaporust too but I'm going to try molasses next.  

[bc.gold 3,403]

7 hours ago, DennisThornton said:

What he said. 

 

But the quickest is hydrochloric BUT it's best to use it outside keeping an eye on it's progress AND it will harm good metal if you leave it long enough.  I think any acid will work with the strongest being the fastest and the weakest with the least downsides other than time required.

 

I'm fond of electrolysis and Evaporust too but I'm going to try molasses next.  

Coka Cola - phosphoric acid

 

 

[DennisThornton 4,769]

6 hours ago, bcgold said:

Coka Cola - phosphoric acid

 

 

Yep!  Just takes longer.  You can watch strong hardware store hydrochloric work and remove rust and to a lesser degree hardware store phosphoric too.  Coke?  I'd have to add some rum to mine to sit that long.

Edited December 11, 2020 by DennisThornton
and sit