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PHOSPHORIC ACID - a pictoral

Discussion in 'The Hokey Ass Message Board' started by 53choptop, May 6, 2008.

  1. 53choptop
    Joined: Mar 5, 2001
    Posts: 1,197


    I know this has come up several times, I just wanted to to give you guys some comparison pics of how this stuff works and looks.

    Sanding the rust off does not get into the crevasses of the metal like naval jelly or phosphoric acid does.

    I just did my car a few weeks ago.

    I used straight phosphoric acid (or Ospho to some of us) without diluting it and applied it with a paint brush, you can buy the acid at homes depot, lowes etc. I have never diluted it, I think it worked faster, and if treated quickly it wont harm the metal.

    Since the acid is a liquid, it is very runny, so I put it in a plastic cup and brushed it on in sections, if you dab it, it will foam up and somewhat stick to the side of the door for example, let it sit for about 10-15 minutes and started scrubbing using stainless steel pads. Once the metal looks clean, I washed the metal with soap and water using a wet rag, if you hit bare metal with water and dry it, it will NOT start to flash rust, someone asked me about that last time. If you look at the dash thats the way the doors used to look. On the really rusty parts it will be necessary to do it several times.

    I also used stainless steel pads from Wal-Mart (you can find those in the house cleaning section of the store), not a wool pad, the stainless steel pad really cuts into the rust.

    And thats it, I took side by side pick of how the rust gets converted to a white powdery substance after sitting all night, if you apply another coat of the acid and start scrubbing you will get clean metal.

    Attached Files:

    tommyd and brando1956 like this.
  2. raven
    Joined: Aug 19, 2002
    Posts: 4,661


  3. DrJ
    Joined: Mar 3, 2001
    Posts: 9,418


    I just cleared off Wife's garden tool shelves and found some Miricle Grow liquid leaking and it made a hole right through the metal shelf.
    Reading the label it says this product is mostly Phosphoric acid...
    Ya think I can (or should) put the rusty metal parts on the lawn and just "fertilze" the lawn while derusting the metal at the same time?
  4. Roothawg
    Joined: Mar 14, 2001
    Posts: 22,515


    2 questions..

    1. Isn't that the same as the acid etch used before priming?

    2. If not, how will an epoxy primer react with it?

  5. 53choptop
    Joined: Mar 5, 2001
    Posts: 1,197


    1. kind of yes, if I am not mistaken, acid etch is diluted phosphoric acid with alcohol, and used as sort of a cleaner/protective coat, phosphoric acid leaves a thin coat of iron phosphate which keeps metal from rusting, (experts chime in on this one)

    2. I attached a photo of my dash that was treated with the acid, cleaned then expoxy sprayed, there were no reactions and adhesion was very good, I had the truck like that for 2 years and it held up fine.

    I have had no problems in the past, I learned of this about 13-14 yrs ago when the first car I had painted by a buddy of mine introduced me to it, the car was treated with the acid, painted, epoxied, primed then painted. The paint is still holding up.

    Attached Files:

  6. mojo273
    Joined: Mar 30, 2006
    Posts: 394

    Member Emeritus

    When then acid is diluted or dry is it safe to dispose of?
  7. atomickustom
    Joined: Aug 30, 2005
    Posts: 3,408


    I didn't know you could scrub the rust off!
    I have used Ospho straight by brushing it onto rust, letting it dry overnight, and then just giving it a quick wipe with lacquer thinner before putting bondo or primer directly over it (this was lacquer primer - it was the early 1980s!). I did that on a '78 Ford wagon that had patches of heavy surface rust all over the body, and I drove that car every day for 2 or 3 years in Northeast Ohio weather and none of those spots ever came back in that time. It still looked like new the day I sold it.
  8. MP&C
    Joined: Jan 11, 2008
    Posts: 2,400


    Most epoxy primers are compatible, but the KP2-CF by House of Kolor is not one of them. It will react with the rust conversion coating and form nice small bubbles (lifting) under your paint. This was verified (after the fact ;)) by contacting their tech line, where I did happen to talk to someone that was a previous employee of PPG. He was very familiar with the rust conversion process, and said not to use it at all on the H/K product. To be on the safe side, check your product data sheets for compatibility.
  9. 53choptop
    Joined: Mar 5, 2001
    Posts: 1,197


    Thanks MP&C, kinda changes plans around a bit now that i know that.

    "When then acid is diluted or dry is it safe to dispose of?"

    I think when its dry there is no problem it just turns either black or white depending on how deep the rust is, and again it turns into an iron phosphate powder, don't know about when its diluted, I guess it depends on how diluted it is.

    All I know is that it will stain your concrete if it falls on it and if you are not careful and "wiff" it by accident, it will give you a burning sensation in your eyes and nose. :D
  10. Kevin Lee
    Joined: Nov 12, 2001
    Posts: 7,451

    Kevin Lee
    Super Moderator
    Staff Member

    I would like to know this as well. Also wondering if I apply it to my car Friday night then roll it out to the curb to scrub and wash Saturday morning... would I end up with a big discolored spot on my street?

    I assume existing paint and filler are largely unaffected? (and would need to be removed
  11. 53choptop
    Joined: Mar 5, 2001
    Posts: 1,197


    the answer is no it will not discolor your curb IF the acid is dry, wet acid will

    and do not apply it to paint or filler it will cause problems, that is why I started using a brush as oppose to spraying it, you can keep the acid contained a bit more, but of course there is a possibility it will run, it ruins paint and filler, i think this is where naval jelly come in and it will stay put.

    Depending on what you want to do after you clean it, this is what will happen, if you look at the dash picture, the white residue is what the rust turn into if you leave it over night, iron phosphate, by that time the acid has done it job and dried out, in this case you can just scuff down the the remaining powder with a wool pad, it actually will protect the metal a bit more because you are not taking all the iron phosphate off. I have done that before and the rust won't come back even after driving in all weather.

    Now if you want a super clean looking metal, then appy another coat of acid, scrub and wipe, since this will be runny and wet it will stain your curb, I place down a whole bunch of cardboard and let the cardboard soak whatever fall onto it. Remember water dilutes it so if it falls on concrete quickly rinse it off with agua.
  12. fleetbob50
    Joined: May 1, 2006
    Posts: 306

    from Waco,Texas

    If Your Worried About Whether Its Safe To Dispose Of Just Look At The Lable On Your Soda Next Time You Pick One Up,
    All Of Them Use It For Carbonation, Just Not At The Strentgh You'll Be Applying It At:d
  13. Tim
    Joined: Mar 2, 2001
    Posts: 13,522

    from KCMO

    or you could mix something into the stuff your throwing out that would nuetralize it?
  14. Fairlane Dave
    Joined: Mar 23, 2007
    Posts: 634

    Fairlane Dave

    Great pics to look at while sipping on my Diet Pepsi! (most brand name sodas have it added for that "zesty" taste)

    Time to re-think my beverage choices...
  15. I have used the stuff called " Right Stuff " sold at Advance Auto stores works Good
  16. 53choptop
    Joined: Mar 5, 2001
    Posts: 1,197


    Tim, I don't know, what I usually do is let it dry before i throw it out. For example if i have cardboard that the acid lands on (it wont eat through the cardboard or anything, because I dip the pad into water for easier scrubbing, so by the time the acid hits the cardboard it actually has water in it already), I just let it dry and the throw it away.

    I wonder if you can just use baking soda? I know that neutralizes concrete stain, when your staining concrete.
  17. If you use this stuff (or any of those metal preps that use phosphoric acid in them), make sure the metal is COMPLETELY DRY before trying to paint it. If your metal is very rough and porous, the acid can sit there in the pores for a long time. It'll all be a hazy powdery gray color when it's dry, but if there's still moist areas, they'll show up as darker patches. It dries very slowly. If you paint over it when it's not completely dry, the paint will bubble up and turn weird. A stainless steel toothbrush-shaped brush like you use for cleaning up Mig welds works well to scrub out the rust from pitted steel while you're etching it. Or something like an ice pick in really deep pits to speed up the etch. If the rust is greasy, use some solvent to remove the grease first, because the acid won't get through the grease.

    I don't mess with those chemicals much anymore though. I like abrasive blasting.
  18. Redneck Smooth
    Joined: Apr 19, 2004
    Posts: 1,344

    Redneck Smooth
    from Cincinnati

    I guess that's why soda eats the corrosion off of battery terminals, huh? I'm gonna try this this weekend on all the crap I just stripped off my olds for cleaning...
  19. What does it do to chrome and aluminum?
  20. once the acid is washed with water it becomes nuetralized...PPG makes metal conditoner as well as aluminum conditioner sold by the qt & gal.....phosphoric acid is the best way to clean bare metal for primer. just my 2 cents..
  21. 53choptop
    Joined: Mar 5, 2001
    Posts: 1,197


    stain it, you can buff aluminum, but chrome...just avoid it all together.
  22. 53choptop
    Joined: Mar 5, 2001
    Posts: 1,197


    Yes, Yes, and Yes, thanks!
  23. belair
    Joined: Jul 10, 2006
    Posts: 8,865


    It will attack cement. Your garage floor and driveway will pit nicely if you don't hit it with water.
  24. 85-percent
    Joined: Apr 5, 2005
    Posts: 323


    My input

    I use any of the metal prep type products from the auto paint supply house to home depot.

    The cheap stuff is used for derusting. soak, apply grind wire wheel, do what you gotta do.

    the good stuff is diluted...uh maybe 3 parts water one part metalprep?

    For stuff to be seen and painted and sheet metal like, i wiped on about 1 square foot, rubbed it in while wet. Then, while its still wet, quickly dry it off so as to leave no white stuff. metal looks like its got a very light blued finish - gives off faint colors red- maroon?

    let it dry for hours if not over night. if you dripped into crevases, blow it out and try to dry out, if only for what always happen when painting if you wet sanded.

    I'm always aghast at all the people out there painting over bare steel with only lacquer thinner or acetone or any other paint solvent, WITHOUT "PICKLING"!

    Those guys got the "tooth" of a mirror and all layers down to bare can be lifted off with compressed air!


    -90% Jimmy
    Joined: Nov 27, 2007
    Posts: 542
    from New Jersey

    Where would I look for this in Home Depot

  26. plym_46
    Joined: Sep 8, 2005
    Posts: 4,018

    from central NY

    Concrete cleaning and etching supplies. Or at swimming pool supply places. I have used vinegar which is 5 % acetic acid. Pour a gallon in a plastic tub and let your small pieces soak. True value and ACe have a spray called The Stuff for Rust which is a phosporic acid with a buffer and some other things. It will keep bare metal rust free for quite a while. I spraye it on after the vinegar treatment.

    Vinegar is slow but it is effective.

    I am thinking of using a recirculating bath of vinegar to work on a hood. My plan is to buy a cheapie kiddy pool, but about 5 to 10 gallons of vinegar in the pool and then pump it with an old fish pond pump to run a constant flow over the hood. Collect the flow in the pool and pump it back around. Vinegar is easy to dipose of just flush it. or pour it down the drain.
  27. Toymont
    Joined: Jan 4, 2005
    Posts: 1,379

    from Montana

    Yrs ago I used Rustmort on my 55 chev cab, after I had it in bare metal but before primer to clean all the little crannys. I put it on, left it overnight, then pressure washed it and had to drive like 45 miles to my brothers where we wiped it down and put epoxy primer on it. I probably haad it in primer for 5 yrs or so with no problems. The morning after putting it on the cab looked like it was peeling from a real bad sunburn.
  28. toddc
    Joined: Nov 25, 2007
    Posts: 981


    So does the Fluoride in tap water:rolleyes::rolleyes::rolleyes:. We're all going to die of something:eek:
  29. Mark in Japan
    Joined: Jun 19, 2007
    Posts: 1,466

    Mark in Japan

    I never take acid treatment advice from people who don't start with "Gloves/Eyeglasses/Ventilated area etc"
  30. timebandit
    Joined: Feb 13, 2003
    Posts: 188

    from Norway

    Muratic acid works great on heavy rust. A lot stronger than metal prep (phosphoric) acid. You can buy it at Ace as a swimming pool additive. The steel will flash rust in minutes though. Then wash with metal prep, and later a neutralising wash with baking soda and water. Dont use it inside your shop. It will eat concreat and will rust all uncoated metals inside your shop. Including tools. And yes wear goggles and thick rubber gloves.

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