Removing Rust with Citric Acid

Discussion in 'Paint & Body' started by Lakeroadster, Jun 16, 2013.

  1. Lakeroadster

    Lakeroadster Member

    Jan 23, 2011
    Central Colorado
    Rich 5150 posted a link to this article in his build thread.
    I thought it was such a great tech. tip that it was worthy of it's own thread. Thanks Rich for enlightening us about this.

    Removing Rust with Citric Acid by James D. Thompson

    A quick, simple, and safe method of removing rust from your old tools (or anything else for that matter) is to immerse the rusty parts in a solution of citric acid. There are many questions asked about citric acid and I will try to answer some of them here. These are my personal opinions only, and I am solely responsible for them.

    Q: Where do you get citric acid and how much does it cost?

    A: Look online, or locate a brewing supply store. I buy mine at a local brewing supply and it costs about $17 for 5 pounds.

    Q: Will the acid hurt anything?

    A: I haven?t seen any damage, but I don?t leave my parts in the solution for a very long period of time. Your mileage may vary if you leave the parts in for a really long time.

    Q: How much do I need?

    A: It depends on how many rusty things you want to clean. My 5 pounds has cleaned a lot of tools, and I still have 3 pounds left.

    Q: Can I re-use the acid?

    A: Yes. When you have finished with cleaning any parts, put the acid into a plastic container and save it for the next job. If you like, you can replenish the acid with fresh powder to keep the strength up.

    Since it is fairly inexpensive, I toss mine when it starts to look nasty. It is environmentally friendly, so you can toss it down the drain when you need to dispose of it.

    Q: Is it safe, and does it have a nasty odor?

    A: I put my hands in it all the time without any harm. It does sting in a fresh cut though. It has no odor.

    Q: How much do you have to use?

    A: I put a cup of powdered citric acid in a gallon of warm water. Others say they use a lot less. My reasoning is this: I want the job over and done with as quickly as possible.

    I don?t like to leave any chemistry out overnight. My preference is to stay with the parts in the acid until they are clean.

    In the picture story that follows, I was finished within 25 minutes.

    Q: Do you have to agitate the solution?

    A: Probably not, but I scrub the parts as they are soaking using a soft wire brush. This gets the acid into the rust faster, and when I bring my rust free parts out of the acid they are clean.

    This is what a 5 pound bag of citric acid looks like. I tore off the bottom left corner, and I pour the powder out from there.


    Here is a mildly rusty Stanley #4C plane all disassembled and ready to go into the acid bath. The knob and tote will not go into the bath. I don?t know whether wood is completely safe in the acid. Most galoots think the acid does no harm to wood. I still don?t put wood in unless the wood cannot be removed from the metal. I always wonder if any residual acid trapped in the wood might cause rust later on.


    Here are all the parts soaking in a gallon of fresh citric acid solution. Notice that the temperature of the solution is about 62 degrees. Rust removal is slowed down with low temperatures.

    I use a soft wire brush to speed up the process of rust removal, scrubbing the parts as they soak. In this particular case, all the rust was removed in under 25 minutes. There is no problem with putting your hands into the solution.


    Here are the clean parts, all washed, dried, and oiled. It is important to oil the metal parts right away as rust will form quickly if you do not.


    This is the plane after re-assembly. I do not think that it looks over cleaned. After a good sharpening and adjustment the plane cuts fluffy curlies.


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