hard rusty sheet metal

Exterior, Paint & Bodywork

  1. swisherred

    swisherred Well-Known Member

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    My roof has a layer of rust that just doesnt seem to want to come off. I have used 80grit and it takes off the top surface rust, but the hard layer underneath just doesnt budge. I want to paint my roof, but dont want future problems. Do I grind through this? Its almost like hot rolled steel...it isnt scaling...what can i do here?
     
  2. mr. fix it

    mr. fix it Old Man with a Hat

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    Scrub the roof with a user friendly acid like Acid Magic
    I buy it from TSC
    Do a test and go from there
    Have solution of baking or laundry sofa to neutralize it after you get the results you are looking for
     
  3. swisherred

    swisherred Well-Known Member

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    hell...nevermind...I just tried 36 grit and it cut through...just have to be careful, the metal under the rust layer is softer.
     
  4. mr. fix it

    mr. fix it Old Man with a Hat

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    Another option is to clean it up as best as possible and use a rust encapsulating paint like Rust Bullet
     
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  5. mr. fix it

    mr. fix it Old Man with a Hat

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    You are right that a 36 grit will cut through and take precious good metal with it
     
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  6. mr. fix it

    mr. fix it Old Man with a Hat

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    Good luck with whatever course you go with
     
  7. swisherred

    swisherred Well-Known Member

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    If I dont have to take it off, id rather not, but dont know how to keep the rust from creating future issues under the paint.
     
  8. swisherred

    swisherred Well-Known Member

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    I have chassis saver, but I dont know how it does as a base under primer...
     
  9. mr. fix it

    mr. fix it Old Man with a Hat

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    I would google it then to make sure it is sandable
    If yes then it sounds like it will work
     
  10. swisherred

    swisherred Well-Known Member

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    It says it can be topcoated if properly scuffed. I just don't know....it says you can use epoxy primer under it..but they prefer DTM. I think I will try 60 grit and see if I can lightly break through enough that the 80grit will take the rest off.
     
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  11. pomonamissel

    pomonamissel Senior Member

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    doctor x rust remover , spray it on , wash it off . then primer n paint .
     
  12. swisherred

    swisherred Well-Known Member

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    I've looked at DRx and it looks good. Have you had any experience painting epoxy primer over it afterwards?
     
  13. bigmoparjeff

    bigmoparjeff Senior Member

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    Epoxy will be fine over Dr X, or any other chemical rust remover. The secret to all those products is to keep the surface wet until the rust is gone. Try not to do it in the sun, or you'll have to use a lot more product due to evaporation. Scrubbing occasionally with a wire brush, a wire wheel in a drill, or scotchbrite will help too.

    I did some surface rust removal on this Neon for a customer, though I can't remember what product I used. I think it was either the stuff from Hirsch or Safest Rust Remover. I'll keep wetting it down while I find something else to do between spray downs. On this car the rust went in really deep, since it was salt air rust. The spots that still weren't clean by the end of the day got soaked paper towels, and I covered everything with plastic and let it sit overnight. I was doing this in late October, so it was fairly cool and the chemical process wasn't as strong as it would have been in warmer weather.

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    This is a close up of the roof panel. You can see how deep the rust pits went. After you wash the surface with water, you'll usually get some orange staining that looks like rust, but it actually isn't. What you are looking for is that it's no longer dark brown or black down in the rust pits.
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    This job was just a preservation, so I painted the panels with whatever paint I had left over from other jobs. The roof ended up silver, and I had enough green to do the fenders and quarter. I never did take any decent pictures of the finished car, just a few in the too dark shop.

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    Jeff
     
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  14. swisherred

    swisherred Well-Known Member

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    That looks exactly like what I am contending with. Thank you for the in depth explanation.
     
  15. swisherred

    swisherred Well-Known Member

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    So I tried what I could find locally...it did ok...removed all the surface rust but not the hard stuff. I went over the entire roof with 36 grit feathering across the hard rust and removed the actual rust layer. I still have a very black surface which I found to be a stable low oxygen rust that actually prevents oxygen from getting to the parent metal. From what I understand, I can paint over that. FE3O4...it shouldn't spread as long as I get it covered soon. I will clean it again really well to get any rust dust off and media blast it to get into any pits then epoxy it. It should last decades.
     
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  16. bigmoparjeff

    bigmoparjeff Senior Member

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    You didn't mention that you had a blaster. That would be the preferred way to deal with the rust from the start. What kind of blaster and media do you have?
     
  17. swisherred

    swisherred Well-Known Member

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    HF blaster with coal slag....works great on most stuff.
     
  18. bigmoparjeff

    bigmoparjeff Senior Member

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    You should be able to do all the rust on the roof with that set-up, as long as you don't go too high on the pressure. You always need to be wary of warping sheet metal when blasting. Anywhere near the edges of the roof, there's no concern at all. As you get about 3 inches or more from the edges, then you'd probably want the pressure down around 80 psi at the compressor, maybe as high as 100 depending on the pressure drop to the blast gun, and hold the gun back a bit further from the surface. Blast first, then follow up with the rust remover chemical to get way down in the pits.
     
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  19. swisherred

    swisherred Well-Known Member

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    The coal slag took off the black rust without damaging or warping the metal. Got it primed last night. Have to go back today and use glazing putty to smooth some small spot out, but I should be able to get another coat on and get it painted over the weekend.
     
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  20. bigmoparjeff

    bigmoparjeff Senior Member

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    :thumbsup: