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Alrighty,

So I have a '69 Cadillac Fleetwood 75 Limo. It had a vinyl roof. The metal underneath is really rusty, but not swiss cheese. Well, not yet.
I've tried MANY times to remove, convert, neutralize the rust, but it just keeps coming back.
Whats funny is that it only comes back on the top.
The sides and back that are rusted just as bad don't seem to come back.

Originally, I used rust converter, then fiber glassed (mat w/resin) over it. The rust came back and broke through the fiberglass.
Then I scrapped/grinded all the fiberglass off, and converted it again. This time I only used the resin. Sanded that all down, primed and bed lined it. It came out AMAZING. Then the rust came back, and broke through again.

Now I'm trying to grind off the bed liner, primer and resin. I'm doing small sections at a time. I'm taking the metal all the way down using a flap wheel on a grinder and 3M strip & clean discs. I'm converting again, but the converter says to wait 48 hours for it to fully cure. Then I go over it with Rustoleum Rusty Primer.

However, by the time two days goes by, there are little dots of rust all over. The car is outside because it can't fit in my garage. I do have it under a 10x20 tent with walls. Also, after I apply the converter, and wait a few days, If I sand it, under the blackened top layer, there is still rust.

I've also tried 'pool' acid (Muriatic Acid), with mixed results. It seems to work awesome at first, but then doesn't stop the rust. I've washed it off with soap and water, just water, baking soda, and still the same.

I know that I should replace the roof, but there are none available.

And no, I can't take a regular Fleetwood and section it, because the shape is different.


I just can't see why the top only comes back on the top?

There is a section of the hood that the paint has flaked off and it rusted. I used the converter on that small section 3 years ago, and the rust hasn't come back there.


Any suggestions?
 

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There was some bad metal back then. A friend bought a new chevy PU and the doors and fenders had to be replaced in a year.
Might have to cut sections out alternately weld them in and go back to cut the rest of them out and fill in. That way you could try to form the contours in smaller sections. make a template front to rear and side to side for reference.
 
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