Technical Tech: Simple rust removal with citric acid

Looking on Amazon (homebound due to quarantine, as we all are) I see a tremendous range of prices. This 5# for $10 is about the least expensive. It doesn't say anything about food grade, as most of the more expensive ones do. I'm thinking this is what we want to use?

What says those who are in the know?

Buy or don't buy?

Does anyone have a better suggestion?

tia

 

That tail light is impressive. I have wondered for quite some time what would clean up rusty chrome. Most post are about cleaning rusty metal. Thanks

 

Yep, I had this with mine, started bubbling after 6 months chrome peeled off in 12 months and completely rusted away in 2 years

 

That is a 5lb bag, and the shipping adds another $7.55. I got a 10lb bag on ebay for $25 shipped. That was the best price including shipping that I could find.
https://www.ebay.com/itm/Citric-Aci...e=STRK:MEBIDX:IT&_trksid=p2057872.m2749.l2649

 

I 'm going to have to try this on some doors that are rusty on the bottom. Make a trough to set them in. Hopefully it would work into the seam where the doorskin is folded over the inner panel. I was going to use Evaporust but this would be a lot cheaper. Might even be able to do it with the doors on the car. Get some rain gutter, cap the ends and set it on some jackstands under the door.

 

Once the parts come out of this process is flash rusting a big issue?

 

I'll have to try this. My go to is reverse electrolysis and I do have a blasting cabinet I seldom use. This looks extremely simple and effective...

 

I thought for a while before testing citric acid,that was 2 years ago.Haven`t used the blasting cabinet since then
Just put in the parts and wait,I check every 12 hours or so.

 

It can happen, usually only very light. What I've found is when parts come out I wash with dish liquid and an old brush, just to clear any debris/old paint etc and then dry in an old towel or similar. Seems to stop it.

When first making up the solution I use boiling water, not sure how much that helps.

This is a little expensive, but might help in some circumstances. There is a company called Bilt Hamber who make all sorts of corrosion treatments/paints etc. They have a product called deox-c which is citric acid plus a few other things. It comes in two forms - one is granules that dissolve in water - no point, just use the citric acid powder.
The other form is a gel (https://www.bilthamber.com/deox-gel) the idea is that you can use this in areas where you can't submerge the item. You just daub the gel on, cover with clingwrap and leave it for a day or two to do its thing, wash off when done. I see evaporust have a similar product.

Talkng of evaporust, they don't like citirc acid much : https://evapo-rust.com/citric-acid-...W7jLlFN7OIQsNukZfla7H5ynH-vcyyQ_wIWuB8MHYclOk

I don't know for sure, but I'd suggest that their product actually contaiins citric acid - maybe in smaller amounts. Either way, I've had metal in citric acid for long periods and never seen any damage to the metal itself. I have had it remove paint, but if you're cleaning rust off an item why would you be worried about the paint ? It can actually be useful to remove paint this way.
I do either wash my hands thoroughly or wear gloves when using citric acid though.

 

About flash rusting: as when we remove parts from the engine vat, after rinsing, the air hose should be in your other hand blow drying. That is the only way I've found to keep them as rust free as possible. Use a leaf blower or shop vac if that's all you have.

 

I take my parts to the car wash clean the item up. Then let sit in the sun. A little flashing occurs because of the water. Usually when I have something sand blasted, it has flashed worse before I pick it up. Guess I need to use my leaf blower to dry the item off. Had a header bow unpainted for a year after the treatment. It flashed a bit but not bad. It was completely rusted in many places, I put it in my tank to see how it would work. Blasting would of destroyed the piece. It is hollow and double thickness in places.

 

Handy

 

Good tech, the citric or oxalic acid are good choices. As I have said several times before, the reason acid works on rust is that acid has H+ ions. The H+ react with the Iron oxide to reduce the O- from the Fe+, don't worry about the exact Fe is +3 and O is really 2-. It's the principle that the acid does get weaker as it works, the H+ combines with the O- to make H2O. The acid sloution then also gets Fe+ in solution. The Fe does not go back onto the steel, so you still have the missing metal on your part where the rust was.
Also it is important to clean and degrease the part good as you can. Acid will not do anything to remove grease or oils.
Vinegar or phosphoric or other acids will all work the same way as far as the chemistry. Just the citric or oxalic are easier and more mild to you as the operator of the process compared to some. More dilute acid will just take longer, which sometimes is a good thing.
It is also a good idea to neutralize after rinsing using baking soda solution. Although a thorough pressure wash is probably good to remove just about any remaining acid on the surface. Better to be safer with the neutralizing.

 

Well I walked up to my local specialty food shop and picked up a 5lbs bag of citric acid (man) for $9.00 CDN which is better deal than Amazon. Anyway I have two exhaust manifolds and two seat racks waiting for the magic! Again, I'm a big fan of reverse electrolysis but I must say this is a lot easier if it works as well. I'll check in 24 hours ..

 

You'll love it.

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I suppose this is the basic process with using Coke to clean up rust but a heck of lot cheaper. I prefer Pepsi anyway...

 

Not sticky either!!

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i have been using citric for years and previous to that i used evrything else available,but citric is the best of the lot.
here in australia i buy 25kg bags (50lb) for about 50 bucks so it is very cost effective. after soaking the parts in the mix idry them off and they then flash rust...no problem...i then mix up some phophoric acid (ranex) in a small bucket and with a rag dipped in this mix i then just wipe the parts liberally all over then just let air dry......panels that i have done like this are still in the same condition years later....if kept out of the weather.
it was mentioned about seamed panels well what i do is after taking them out of the mix i then put them in a container of water mixed with baking soda and the neutralises it then dry it off and then rub down with phosphoric acid (ranex)
it was also mentioned about alloy dissolving in citric....well i have done panels banded in alloy and they have not deteriorated in anyway BUT die cast will just dissolve as soon as you put it in the mix....this is basically what i do and it has worked for me for the past 15years
all these ingredients are available from bubble and shampoo shops and are quite cheap

 

If you have any unused... keep it with the label. I keep mine in a used pretzel container and leave the label inside with it or tape it to the outside is also good. It looks a lot like something out of the Scarface movie...

 

another thing i do with citric....any of my complete motors that i have stored in my shed....i block the botom radiator hose and remove the thermostat and then fill the engine with citric acid and occasionally spin the water pump....this does 2 things firstly removes the rust and scale out of the motor and secondly keeps the water pump from drying out...then after a period of time i empty and flush the motor and you want to see the crap that comes out...i then mix up some soluble oil that engineers use with water and fill the motor up again and this stops it from rusting up again.
another thing i keep a plastic container with a screw top....anything up to a gallon....this i keep 3/4 full with citric and when i hjave a handful or so of rusty nuts and bolts i soak them for a while and when removed put them into some phosphoric acid and they come out new again

 

where cansomeonne get phosphoric acid? I suppose this neutralizes the acidic acid or just leaves a protective coating on the parts?

 

I've made up citric acid gel by adding xanthan powder to the acid solution. Seems to work just like the deox-gel.

 

I did the same so I could get the rust off of my roof. Laying down paper towels and spraying them every hour or so with citric acid solution seems to work too. Just can't have wrinkles in the towel.

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An idea: If you want to do something large like a door, I would visit some of the local trucking or factories and try to get some of the old crates they throw away. I know the company I used to work for threw lots of them away and if someone wanted one, they were glad to get rid of it. Anyway, get a crate large enough to hold the door laying flat, and then put some of that black plastic drop cloth stuff in it and let it drape over the side. Then you have a watertight crate and you can throw the liner away at some later date. Cheap and effective for larger parts like fenders and bed sides.
Guess you could do a cab or body if ya had a big enough crate.

 

Glad to see this one back up again. I grabbed the backing plates off the shelf, they've been sitting in my garage untreated and still show hardly any signs of surface rust. I should add in the OP I said no odor, well it does have a slight smell but no fumes or anything noxious. I do it in the garage were my wife does laundry and she'll never complain.


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Would it harm brass core plugs?

 

About 2 years ago I put a hood off a 58 Pontiac in my tank. The top edge stuck up out of the solution. It got cold out and was frozen in the mix for 2 months. Pulled it out and flipped it around for 3 weeks more. There was a hard edge where the water line was. Took a bit of sanding but got it removed. Only rinsed it off with water. The car is painted now. No after affects of the citric acid yet. The trunk was dipped too.

 

Lets hear more.

Ive used oxalic and now citric acid for a few years now. Looking for a method to load a pump sprayer and douse the bottom on a car and have it hang or cling. I could shoot it thru and undercoatimg gun if its really thick.

The cost is low enough, I could recoat once or twice a day for some time.

Any aluminum would need to be considered and not coated.

 

I'm looking at doing my inlet manifold with citric, but a bit concerned about the flash rust, as I wont be that easy to dry the runners and water ways, and adding more water with bicarb in just seems like it will make the flash rust worse, what would 'users' advise?

 

just go ahead and do the manifold then when happy with it mix up some phosphoric acid or buy some ranex and soak it in a tub or whatever as long as the manifold is submerged and flip it over a couple of times (air pockets) and then when you are happy with it pull it out and let it air dry and you are good to go