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What type of metal prep acid is best?

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  • What type of metal prep acid is best?

    What are you guys using as a final step to clean rust off steel? The fender is clean, but looks like it may have had surface rust at one point in life. Is there a solution that I can brush or spray on to clean the steel down to its pours? I have Por 15 metal prep. Anything better?

    Thanks,
    Nate

  • #2
    The shop I frequent uses Cromax products (formerly DuPont). 5717S etching solution and 5718S neutralizer. The 5717S is a concentrate that is diluted in water and scrubbed via Scotchbrite and rinsed off. The 5718S is then applied full strength and rinsed off.
    Last edited by rockne10; 12-09-2015, 10:28 PM.
    "All attempts to 'rise above the issue' are simply an excuse to avoid it profitably." --Dick Gregory

    Brad Johnson, SDC since 1975, ASC since 1990
    Pine Grove Mills, Pa.
    sigpic'33 Rockne 10, '51 Commander Starlight, '53 Commander Starlight "Désirée"

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    • #3
      I have had good luck with ospho from Sherwin Williams. Steve
      sigpic

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      • #4
        Ospho-have used it for over forty years, no failures. Make sure that it doesn't contact any existing paint or it could lift it.

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        • #5
          "Kleen-Strip prep and etch" phosphoric acid completely removes rust. It's a liquid and can be brushed on, sprayed on or wiped on with a clean rag. Leave it on your fender overnight then rinse it thoroughly with water and blow dry. It etches the surface and can be painted over with your primer. It's available at Lowes and is comparatively inexpensive compared to others on the market. Very effective.

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          • #6
            I used Ospho to treat my new floor pans and other areas after stripping the interior. Epoxy primered over it with a primer that specified it was ok to use over an acid prep. Haven't seen any issues to date (about 1 year).

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            • #7
              The main active ingredient in Ospho metal treatment is phosphoric acid. Jeeeze!

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              • #8
                Thank you. I'll check out the kleen-strip. I'm just starting to weld in the patch panel on the fender, but we are moving this weekend so I won't get to it until next week.

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                • #9
                  Agreed. Ospho is just phosphoric acid, I just get it at ace hardware with a coupon and it's the cheapest around here I could find.

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                  • #10
                    Most of these product are Phosphoric acid AND they have a solution to assist in keeping it from running off AND drying out. But, yes, the active ingredient is PA.

                    Just curious, most presumably rinse off with water. It seems no matter how quickly I dry off with a rag/hot air (and I'm talking seconds, not minutes) there is often flash rust. What do you do to avoid it? Or, how do you treat it? It seems like a dog chasing its tail when rinsing with water. There are times I've used brake cleaner to get the phosphoric acid off to avoid the flash rust.
                    '64 Lark Type, powered by '85 Corvette L-98 (carburetor), 700R4, - CASO to the Max.

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                    • #11
                      I followed the directions on the Ospho bottle which state: "NEW METALS - For new ferrous or aluminum metals: remove dirt, grease, or oil; apply OSPHO, let dry overnight, then paint." So I didn't wash it off. Hopefully it wasn't a mistake but, as I said, it has been about a year since I primed the interior and I don't have any peeling or bubbling or pulling off of the primer that I have noticed.

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                      • #12
                        I believe the original post was an old fender not "new metal." The process of rinsing is to remove the acid from any existing old paint as it can be problematic. Rinsing on "new metal" is not necessary. The entire process for either new or old metal should be done in a dry atmosphere. I've never experienced "flash" rusting but I suspect if you're trying to do this process in a damp or humid environment you never would be able to actually dry the material your treating and then it would be like the proverbial dog chasing it's tail.

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