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Old 03-24-2020, 02:22 PM
Tomaso Tomaso is offline
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Default Will epoxy primer and body filler stick to brass weld?

Hi guys,
Thereís a part on the quarter panel side that appears to be brass welded back then. And itís the paint is flaking off in that section.. if I grind the area, sand and get rid of the rust. Will epoxy primer stick to the area, and could I then apply a metal filler or body filler properly over it?
Thanks, Mike

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Old 03-24-2020, 03:33 PM
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Specifically what area of the quarter panel are you referring to? Possibly you are referring to the area where the upper quarter joins the roof panel and the gap is lead filled.

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Old 03-24-2020, 03:37 PM
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No. This area here. Looks like part of quarter was replaced at one time and brass welded..
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Old 03-24-2020, 05:25 PM
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Need to grind all that out and see what's going on.

If it is brass brazed...I suspect they didn't get the metal hot enough to fuse things together good. And that's allowing some flex to crack the filler and paint then letting water in. Getting panels that size and shape hot enough to braze with brass would have caused a bunch of warping.

Gotta see what's there first
Clay

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Old 03-24-2020, 06:29 PM
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I learned many years ago when a panel is brazed to another piece of metal that you absolutely have to get rid of the glassy looking residue that comes from the melting of the flux used on the brazing rod.

About 50 years ago, before there were MIG welders in every body shop, body men that didn't know how to oxy acetylene weld with steel rod, would use the brazing process, similar to soldering with brass. Brazing was easier to learn than the welding process, so many times it was used as a substitute for welding when replacing body panels. If you wanted anything to stick to the brazed joint, you have to remove the flux residue, either by sand blasting, or grinding.

It's very possible the flux residue was never removed, I know for a fact that no filler, or primer will bond well to the flux residue. I used to work for a guy that did body work as the bottom guy that did all the sanding, and crappy work. He sand blasted the brazed area after he was done, before he applied any filler so it would get a good bond, and remove all the flux residue.

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Old 03-24-2020, 06:36 PM
Tomaso Tomaso is offline
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Quote:
Originally Posted by Sirrotica View Post
I learned many years ago when a panel is brazed to another piece of metal that you absolutely have to get rid of the glassy looking residue that comes from the melting of the flux used on the brazing rod.

About 50 years ago, before there were MIG welders in every body shop, body men that didn't know how to oxy acetylene weld with steel rod, would use the brazing process, similar to soldering with brass. Brazing was easier to learn than the welding process, so many times it was used as a substitute for welding when replacing body panels. If you wanted anything to stick to the brazed joint, you have to remove the flux residue, either by sand blasting, or grinding.

It's very possible the flux residue was never removed, I know for a fact that no filler, or primer will bond well to the flux residue. I used to work for a guy that did body work as the bottom guy that did all the sanding, and crappy work. He sand blasted the brazed area after he was done, before he applied any filler so it would get a good bond, and remove all the flux residue.
Thatís what I think is there too because you can see the glassy/glue look appearance. Thereís no filler, all gone, just the braze and rusted metal. If I grind that down, then can I epoxy and metal fill? It looks like a solid weld from top, I wish I took a better picture. You would see what I mean...
Thatís what Iím wondering if I ground that down and put metal filler over it?

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Old 03-24-2020, 06:42 PM
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Quote:
Originally Posted by Tomaso View Post
That’s what I think is there too because you can see the glassy/glue look appearance. There’s no filler, all gone, just the braze and rusted metal. If I grind that down, then can I epoxy and metal fill? It looks like a solid weld from top, I wish I took a better picture. You would see what I mean...
That’s what I’m wondering if I ground that down and put metal filler over it?
Yes, as I said, either grind off all the flux residue, or sand blast it, two ways to arrive at the same end result. The flux residue is smooth and slippery, just like glass, you'll never get anything to stick directly to it. Back then there was no epoxy primer, just lacquer or enamel based primer, I assume it will bond if you get the flux residue off of the brazing. I'm however not a body or paint guy, I just worked for a body guy as the grunt that did all the work he didn't want to....LOL. Someone else will probably have a more definitive answer for you.

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Last edited by Sirrotica; 03-24-2020 at 06:51 PM.
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Old 03-24-2020, 06:44 PM
Tomaso Tomaso is offline
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Quote:
Originally Posted by Sirrotica View Post
Yes, as I said, either grind off all the flux residue, or sand blast it, two ways to arrive at the same end result. The flux residue is smooth and slippery, just like glass, you'll never get anything to stick directly to it.
So thatís it then. Thatís what it looks like.
Thanks for the advice! Will give it a try once weather is better

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Old 03-24-2020, 11:14 PM
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If you don't mind, I'll give you my thoughts.
I agree with the things Brad mentioned about adhesion problems. And he's right, brazing a panel was considered a sloppy but passable way of getting one "out the door" decades ago. It was never the right way, so I eventually learned to gas weld with steel.
But back to your repair! Because I restore lots of these old cars, they often have a shady past of repairs hidden by filler and paint. Here is what you might possibly do, it has worked for me.
I am assuming that the back section was replaced and possibly (hopefully) overlaps the original panel. If so, you need access to the back of the panel to determine how much over lap there may be. I've seen as much a couple of inches on some cars. Sometimes there are burn traces on the backside, but they were often hidden with undercoating.
If there is enough over lap you can possibly make a cut through both panels, just behind the leading edge of the top panel. This does two things. It gives you a way to remove the repair panel while you dress the edge of the original panel (remove brass and remains of repair panel with grinder or heat), plus it should leave you with two clean matching edges to allow the removed panel to align with a clean original panel. Now the two can be butt welded with no brass to interfere.

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Old 03-25-2020, 10:41 AM
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Default brass

I have heard that if you lead over the brass that it will seal it and allow paint to stick. That is after all flux has been removed. Billk

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Old 03-26-2020, 05:26 AM
Beige1968GTO Beige1968GTO is offline
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Default Flux

The flux will need to be removed regardless of whether itís lead, filler or paint going over it.

It sounds like the failure to remove the flux led to the initial failure and its removal will give a substrate that accepts filler or paint.

Ron

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