Hot Citric Acid Bath

  1. Onoff Member

    Messages:
    984
    Location:
    Sevenoaks, UK
    Well...my own fault...'cos I'm a slack git!



    In the old bath filled with citric acid solution I've left stuff since NOVEMBER.



    The solution has turned jet black. Some components left in there I think might be "losing mass" but aren't rusting as in red rusting.



    The components are covered in a hard, crystalline substance. So hard I have to scrape it off with a sharp knife. Anyone got any ideas what it is? Once you've scraped the lumps off you can, with a bit of pressure crumble them but it's still bloody hard to do. This is one of the mower blades:



    [​IMG]


    Also any ideas of a solution (as in liquid) that might get rid of it quicker than mechanically scraping etc.



    Cheers
     
  2. fizzy Forum Supporter

    Messages:
    5,581
    uk
    Try vinegar.
     
    Onoff likes this.
  3. owas

    owas Member

    Messages:
    1,750
    Location:
    Birmingham
    Crap I left a vice in mine :ashamed::ashamed::ashamed:
     
  4. Sean Another 602 fan

    Messages:
    1,233
    Edinburgh
    Zinc plating of any sort, galv bzp yellow passivate etc goes crusty and white in citric acid. Ive used it to de zinc fasteners before tigging them
     
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  5. Wallace

    Wallace Member

    Messages:
    6,858
    Location:
    Staines, Middlesex, England.
    Brick cleaner does it nice and quick.
     
  6. Onoff Member

    Messages:
    984
    Location:
    Sevenoaks, UK
    Yep, my college made knurling tool and vice are in there somewhere.
     
  7. Onoff Member

    Messages:
    984
    Location:
    Sevenoaks, UK
    Thought I'd have another bash with citric acid. Need to do the couple of spare steel wheels for the wife's Pug, some lawnmower deck parts and some old lifting chains for the BiL. (I started off doing the wheels with electrolysis a while back. It wouldn't get paint off, I tried light sand blasting...then gave up. This time they'll just get a coat of Lidl Baufix black metal paint and be done with it).

    144L blue barrel. 72L of hot water and 10kg of citric acid powder.

    [​IMG]

    [​IMG]

    [​IMG]

    Did think about painting the barrel black to absorb more heat from this lovely sunshine.
     
  8. owas

    owas Member

    Messages:
    1,750
    Location:
    Birmingham
    I've made up a mix of citric acid, bit of baking soda and enough water to make it a paste.. Painted all over the rusty areas, going to leave it a week and do another coat, hopefully it works well
     
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    monky harris likes this.
  9. RaceDiagnostics Forum Supporter

    Baking soda will neutralise citric acid, so not sure that is a good mixture to use on rust.

    Better of using a combination of wire wheel and flap disc on a grinder to get rid of rust there.
     
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  10. The_Yellow_Ardvark

    The_Yellow_Ardvark Member

    Messages:
    12,471
    Location:
    England
    Mix vinegar and flour to a paste, apply then wrap in cling film.
    Takes a bit longer to work, but it does.
     
  11. owas

    owas Member

    Messages:
    1,750
    Location:
    Birmingham
    I kept seeing it mentioned being used to make it more of a paste, I only put a little bit in though and it did make it better to brush on and stick

    Worked well on the subframe parts,
    I will be going over with a wire wheel after too before I paint anything.

    Was there much protection above the subframe on your xk? I know this has had some work done so don't know much is factory but there is hardly any paint.
     
  12. Onoff Member

    Messages:
    984
    Location:
    Sevenoaks, UK
    I might have a crack at making up citric acid + gelatin. Wondering if it'll be paintable and cling to the underside. Also skin over but have an active layer in contact with the metal.

    What I really need is an old swimming pool and citric acid in bulk!
     
  13. Screwdriver

    Screwdriver Member

    Messages:
    5,952
    UK London
    I have tried various pastes with mixed results. I think the acid needs to be able to circulate. If it can’t “move” I find it can become neutralised, used up where it touches the metal and the concentrated acids remain fixed in the paste where it can’t act on the material.
     
    Dcal likes this.
  14. Onoff Member

    Messages:
    984
    Location:
    Sevenoaks, UK
    My post above on Sunday: 10kg of citric acid with 72L of HOT water from the sink tap. You could literally see the stuff working in minutes rather than hours. Nice hot day too kept the temperature up. I have a hunch a squirt of Fairy or any washing up liquid might add "bubbles" to aid the overall effect.
     
    Parm likes this.
  15. RaceDiagnostics Forum Supporter

    The protection on the Xk was virtually non existent.
     
  16. Gragson

    Gragson Forum Supporter

    Messages:
    564
    Location:
    Bucks
    I'm going to be using citric in a normal bucket for some mildly rusted steel parts, starting off with hot water then just leaving and agitating now and again.
    Bit confused on the best ratios, read the below, but what's best ?

    4:1 by volume = 250g / 1L
    19:1 by volume = 250g / 4.75L
     
  17. Onoff Member

    Messages:
    984
    Location:
    Sevenoaks, UK
    The stronger solution will just work quicker.

    I've got a 19:1, 72L solution in a half filled barrel out in the Sun in the garden at the mo. Working a treat. Pop rusty mower bits in one afternoon AFTER DEGREASING and knocking off any obviously rusty bits. Take out the next and give a wire brush to get any stubborn bits off. Stick back in for another 24 hours if need be. Next afternoon take out, rinse in hot soapy water, dry and prime.
     
    Last edited: May 21, 2020 at 1:05 PM
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  18. Gragson

    Gragson Forum Supporter

    Messages:
    564
    Location:
    Bucks
    Thanks for that, might be obvious but would have missed the decreasing bit as well :thumbup:
     
  19. daedalusminos Member

    Messages:
    761
    Location:
    Norwich
    Hard crystals were mentioned forming in an earlier post - this is just the citric acid coming out of solution as the water evaporates to form a saturated solution. Hot water dissolves it off.
     
    ronan likes this.
  20. Parm

    Parm We Will Do Whatever It Takes

    Messages:
    10,936
    Location:
    Towcester
    Ive never bothered with exact quantities and rations. Bung in a couple of table spoons of citric acid into a bucket of warn water and then let it do its stuff.

    Last lot was an assortment of spring caliper measuring and marking tools, left in over night and they were good as gold

    I get the citric acid from the indian grocers. Its much much much cheaper
     
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