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  1. #1
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    May 2020
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    Default Post Citric acid protection

    Hello all

    I am about to give some old panels of my Chev truck project a Citric acid bath to remove some of the rust. Once they come out of the bath they will require repair that make take a few weeks depending on available time. I will be doing one panel at a time. The truck probably wont be ready for paint for a year or so.

    Therefore what should I put on the metal to protect it whilst I do the metal repairs and put it in storage for painting.

    Thanks

    Steve

  2. #2
    BobL is online now Member: Blue and white apron brigade
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    Default

    What sort of repair?
    If its not welding I'd spray a Zn rich primer/undercoat on it right away.
    If its welding I'd just wipe some light oil on it, and put the Zn rich primer/undercoat on it after its been repaired while waiting to repaint
    If it comes back from repair in a rusty state - back into citric acid.

  3. #3
    Join Date
    Apr 2019
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    Adelaide
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    Default

    When I had my car body sand blasted I immediately painted all the dad's metal with etch primer. As I did the rust repair sections I painted more etch primer. Etch primer will not protect against moisture so keep it dry and avoid condensation.

    You will need to neutralise the acid and flush with plenty of water.

  4. #4
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    Sep 2005
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    Bendigo
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    Default

    Use a modern protection, epoxy primer.
    Older primers were hydroscopic and would rust under the paint. Epoxy primer will seal the surface and protect from moisture.

  5. #5
    Join Date
    Jul 2008
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    near Warragul, Victoria
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    Default citric

    I really like the Wattyl Super etch prime, it comes in grey and black , its a epoxy paint with a tough finish.

    With the citric bath, the warmer or hotter the solution is, the faster it will work, its a rather slow method in a cold environment . Its a Summertime job for us Victorians !

  6. #6
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    Apr 2020
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    France
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    Default Rust Protection

    Two things I have found to be good.

    Gibbs oil is a especially made product that stops rust on any metal. Panels tools etc. It works well and can be painted over without any problems. So suits body panels, gives protection for months.
    The other is basically phosphoric acid. This brand you can get at Bunnings. It is much cheaper than Gibbs.
    Not the best phots but you can find Gibbs with Google.
    When you take the panels out of the citric bath they will "flash" rust almost immediately. It helps stop the rusif you get a heat gun on them to dry them quickly.If you wipe them over with either product straight away they can be left for months without further treatment.ranex.jpggibbs.jpg

  7. #7
    BobL is online now Member: Blue and white apron brigade
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    Default

    Quote Originally Posted by Redminch View Post
    When you take the panels out of the citric bath they will "flash" rust almost immediately.
    That's only if you wash them, its the water that does it. Unless you are going to prime or paint immediately I don't recommend washing them.
    Just blow dry with compressor and used a heat gun to get the acid out of the cracks.
    Citric acid is a chelating agent and does not dissolve steel I've done lots of testing on this

    Below shows a test run with the initially heavily rusted steel steel being dunked in various 10% acids (HCl - Hydrochloric, AC = Vinegar, Ax = Oxalic ND CI = citric) and then pulled out, blown dry and suspended in air for 6 days. NO WASHING

    6days.jpg

    Here again after 10 weeks. Oxalic acid wins hands down but the vinegar and citric have also not rusted much.
    These pieces were left hanging up under a back veranda.
    10weeks.jpg

    For general use there's no need to remove any residual like the yellow green ferrous oxalic acid layer - just paint direct over the top.

  8. #8
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    Feb 2009
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    jilliby nsw
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    Default

    Thanks for your input to this thread Bob L. Im just about to start rubbing back and repairing the panels on a '68 cooper S so this information will come in handy to preserve the finished panel prior to paint.

  9. #9
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    Jul 2008
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    near Warragul, Victoria
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    Default prep

    I do this sort of thing in Summer. After removing the part, I do wash it down with water but during Summer that isn't a problem. Before painting with the etch prime, I go over the part with a brass cup type wire wheel mounted on a 5" angle grinder, doing this removes any left over crud and it really polishes up the surface to a nice clean bright finish. Finally use a rag and a solvent, I use thinners , and rub over the surface to remove any residue from the previous steps, lots of gunk will come off with the rag wash. Use good gloves and be careful . If i am storing the part , I wrap it in Glad Wrap , it keeps the air away . A 50 metre roll is cheap

  10. #10
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    Nov 2020
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    Sydney
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    Default

    Further to BobL's post,
    I occasionally use citris, however over the past few years I've used molasses and kephos as I find the item is always ready for the next phase and there's no retreating.
    If there is heavy rust on a part(s) and I'm not in a hurry, I have a 10% molasses bath of 15lts and I put the item(s) in the bath for a week or more. Every few days I clean the foam off the top and when the foam stops, I know all of the rust has been eaten. There is a minor down side to this process in that it eats off any natural protection to the steel.
    I then rinse the item, quickly dry it, then give it a thin coat of phosphoric acid which is then wiped off with a damp rag.
    Once i have a few pieces, I give them a coat of kephos and store away until it needs to be painted, repaired or welded onto a car being restored.
    Cheers, Mick

    PS. This is my first post.
    I play around with cars and currently doing a major restoration of a 1964 Alfa Giulia Spider.

    Quote Originally Posted by BobL View Post
    Citric acid is a chelating agent and does not dissolve steel I've done lots of testing on this

    Below shows a test run with the initially heavily rusted steel steel being dunked in various 10% acids (HCl - Hydrochloric, AC = Vinegar, Ax = Oxalic ND CI = citric) and then pulled out, blown dry and suspended in air for 6 days. NO WASHING

  11. #11
    Join Date
    Dec 2015
    Location
    south coast, nsw
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    Default

    What about a coat of lanolin?

  12. #12
    BobL is online now Member: Blue and white apron brigade
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    Default

    Quote Originally Posted by Wattsy016 View Post
    Further to BobL's post,
    I occasionally use citris, however over the past few years I've used molasses and kephos as I find the item is always ready for the next phase and there's no retreating.
    If there is heavy rust on a part(s) and I'm not in a hurry, I have a 10% molasses bath of 15lts and I put the item(s) in the bath for a week or more. Every few days I clean the foam off the top and when the foam stops, I know all of the rust has been eaten. There is a minor down side to this process in that it eats off any natural protection to the steel.
    I then rinse the item, quickly dry it, then give it a thin coat of phosphoric acid which is then wiped off with a damp rag.
    Once i have a few pieces, I give them a coat of kephos and store away until it needs to be painted, repaired or welded onto a car being restored.
    Cheers, Mick

    PS. This is my first post.
    I play around with cars and currently doing a major restoration of a 1964 Alfa Giulia Spider.
    The thing most people do incorrectly after using acetic/citric/oxalic baths is to wash parts with water - the trick is NOT to wash them with any water but just blow dry with a compressor and provided its left out of the weather it should stay rust free for some time thereafter without any treatment. Oxalic will stay rust free for many months, even years, so no mucking around with washing sticky molasses or extra coatings of PA etc.

  13. #13
    Join Date
    Dec 2007
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    Sydney
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    Love the smell of kephos
    At North Sydney TAFE the head teacher at our resto class wouldn’t let students apply it in the workshop, you’d be banished to outside.
    Works on Tools if your workshop has the rust problems mine does and you don’t want your tools greasy.
    H.
    Jimcracks for the rich and/or wealthy. (aka GKB '88)

  14. #14
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    Nov 2020
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    Default

    BobL, I agree that the part should not be washed with water except for the molasses. It needs to be washed off as it's impossible to paint over.

    Clear Out. Shame they closed that section of tafe.
    We all have fond memories.

  15. #15
    BobL is online now Member: Blue and white apron brigade
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    Quote Originally Posted by Wattsy016 View Post
    BobL, I agree that the part should not be washed with water except for the molasses. It needs to be washed off as it's impossible to paint over..
    Yep agree that sticky stuff has to be removed before painting. I was put off a bit from molasses by the smell and had nowhere else to put the container except inside my shed. I tried putting the tank on the back veranda but SWMBO put paid to that in short order.

    For smallish objects I now use citric/acetic/oxalic in my electrolysis tanks made up out of 150mm and 100 mm diameter PVC pipe. I have several ranging from about 4L to about 8L. They have PVC end caps glued onto the base and a threaded coupler with a an O-ring screw cap on the top. For bigger stuff I use a 50L black HDPE tub.

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