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acid neutralizing question

Discussion in 'The Hokey Ass Message Board' started by kscarguy, Jun 16, 2013.

  1. kscarguy
    Joined: Aug 22, 2007
    Posts: 1,584


    I have a question about using acid to clean surface rust from large areas of sheet metal.

    When I use water to neutralize the acid, the metal seems to re-rust really fast. When I use lacquer thinner to wash away the acid, it works great, but takes a lot of thinner.

    Is there a better way to neutralize the acid and stop the "instant" rust?
  2. reverb2000
    Joined: Apr 17, 2005
    Posts: 441

    from Houston TX

    Someone explained it to me as what you are seeing is actual metals in the city water rusting. Use deionized (sp?) water and see if that works.
  3. woodypecker
    Joined: Jan 23, 2011
    Posts: 300


    Tums for you and baking soda in a bucket of water for the metal.
  4. mashed
    Joined: Oct 15, 2011
    Posts: 1,474

    from 4077th

    Drying the surface immediately with a hair dryer will cut down on the surface rust.

  5. If you use lacquer thinner, you are diluting the acid, not neutralizing it. If you use baking soda to neutralize the acid, the chemical reaction creates a salt. salt = rust
    Hopefully you are using phosphoric acid and when you do, let it work until it dries, you will get a white residue, which will wipe off dry, you will be left with a very thin layer of iron phosphate. You can't really see it but it is there and that is a good thing! Spray your self etching primer over the undisturbed surface. Self etching primer has phosphoric acid in it and it tastes like unsweetened Coka-Cola, ask me how I know. LOL
  6. Buckster
    Joined: May 3, 2010
    Posts: 229


    I used water & then wiped the panel down with mineral spirits, kerosine, or enamel thinner to displace the water. This method worked great here in the southeast where the humidity is high.
  7. kscarguy
    Joined: Aug 22, 2007
    Posts: 1,584


    I like this idea, but thought kerosene will leave an oil film?
  8. BillM
    Joined: May 26, 2007
    Posts: 247

    Member Emeritus

    I'm assuming you are using acid such as muriatic acid. If so, a rinse with water followed by an application of phosphoric acid such as Ospho will give the metal surface a conversion coating that will stop surface rusting and provide a good base for most primers; but check the spec sheets for the primer you are using to check for compatibility. I use PPG DP series epoxy over Ospho with good results.
  9. jfreakofkorn
    Joined: Apr 13, 2010
    Posts: 2,640


    i always used vinegar
  10. chaddilac
    Joined: Mar 21, 2006
    Posts: 13,867


    Vinegar is an acid.
  11. TSP is the best I have found to nutralize chemicals from paint strippers..It is available at any paint store..Tri-sodium Phosphate..just mix with water
  12. Use your acid, neutralize by a wash it with water. Blow dry as you go.
    Now on your flash rust use a metal prep ( also an acid) and follow the manufactures directions.

    That's going to leave the metal with a goofy bluesish greenish sorta yellow hue. That hue is some magical chemical compound that takes the primer and protects from immediate flash rust for a short while till you can get it primed.
  13. koolkemp
    Joined: May 7, 2004
    Posts: 6,006


    I use windex works great before it dries I scrub with windex and a scotch brite then wipe ,blow dry .... , a friend who is a painter uses it to wipe down before painting ...
  14. perrysmith
    Joined: Jul 6, 2008
    Posts: 257

    from Idaho, USA

    Technically, you are in a deep subject. To neutralize a strong acid pretty much requires a strong base like Sodium Hydroxide. To dilute it with water to anywhere close to neutral requires an extreme amount of water. Hydrogen ion is so tiny (that is the acid ion) compared to most ions, that washing it clean is improbable (why I no longer use hydrocloric (a strong acid) for derusting. NaOH (sodium hydroxide) is also known as lye and is often a drain cleaner. It is a strong base and equivalent amounts of it should neutralize your HCl which will yield common salt and water, both of which will wash off with copious water rinse.
  15. 2racer
    Joined: Sep 1, 2011
    Posts: 960


    go to your local pool supply and get some soda ash to neutralize the acid, it mixes with water like baking soda, then take it for a high speed run to dry it...

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