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I have recently debaged my wagon, partially to deal with rust growing beneath the rear VW emblem.

Now I am stuck as to how to deal with the rust. i have grinded, and polished off the rust to bare metal, and then sprayed on a primer. I let that dry for a day, and then when I go to apply the top coat (custom spray can from the automotive shop) i find the primer is not only letting rust grow beneath it, but is also flaking off the metal...

what am i missing here?
 

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Rust returns because it or the moisture that causes it is still there. I'm not an auto body expert, but I think the possibilities are:

a) While the cleaned surface looked like bare metal, really small rust pits were still present;
b) Enough time passed between cleaning the surface and priming that new rust began to form before the primer was applied - this might be as little as several hours; and/or
c) The primer itself was not completely resistant to moisture, thus allowing moisture in.

If the rust isn't removed, or has penetrated through the panel, then surface grinding alone will not clean the area sufficiently - the panel (or the part of the panel that's been compromised) must be replaced.

David Brick
Santa Cruz CA
2001 V6 GLS
 

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The best way to get rid of rust is to sandblast it off...that way you are getting into all the little pits, etc. Then I would use a rust converter/metal prep product on the metal, which I believe forms a protective thin layer over the top of the metal that you just sandblasted, then prime and go on as you normally would.

What sort of primer are you using?
 

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Just sand it all away. Clean it with some surface cleaner, then primer it with some rustoleum. It will convert the rust to primer. After that, wet sand the primer with anything from 1000-3000 grit and then paint the area with your paint. Use a clear and then wet sand that. Process it over.
 

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Wow,lots of bad info there.
Forget cutting it out and rewelding, we aren't talking about rotted quarters here, just some surface rust.

Sandblasting is best as it removes all the oxidized metal including that which might be below the sanded surface. If its a small area, you can just use sandpaper as long as you are able to get all the pitting to smooth metal. No need to go more tHan 220 grit on he bare metal.

If the badge is over all this, you can just paint it, but if visible, the edge of the repaired area will need to be feathered into the rest of the paint.

Since you live in a very humid area, you should use a rust inhibitor like rust away or metal ready or similar. It's an acid that gets rid of any remaining oxidation and bonds with it to stop further rusting.

Make sure your primer is compatible with the touch up paint you are using. Sounds like it may not be.

After feathering the edges, the primer can be finished with 400 to 600 grit.


depending on the touch up paint, you will prob want to feather the edge of the top coat w 600, 800, 1000 grit then polish.

You can avoid some of the blending work if the badge hides it, or if you can use panel lines or the indentation for badge to hide the edges.

Be aware, at your skill level you will prob be able to see this repair unless it's hidden.
 
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