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Old 01-06-2011, 08:42 PM
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Ghost lines from welded patch panels

First off, this is my first post. figure i should say thanks to all of you since i have been learning so many new things from this site that have made my life a little easier. I am a collision painter. I do all of my own personal bodywork and i have been doing it for a few years. this problem has been bothering me lately though. I am having this issue where all of my patch panels have been welded in on my car. I did the bodywork last winter, sprayed it right after and i noticed the ghost spots once it sat in the sun for a couple days. a block and buff will hide them for a month or so but then they faintly re appear over time. my process was the following:

1) cut filler panels to exact size, same gauge sheet metal as factory panel. stripped paint back ~4" around are to be welded

2) butt welded in place. about 5 tacks spread apart, let panel air cool, then 5 more in between previous, etc. once it looked solid i ground down the welds, used my hand sand blaster gun to clean out the small gaps between the welds, then welded the remaining gaps up. (miller 180 w/ gas)

3) ground down the remaining welds

4) I have done both of these processes on 2 different patch locations on the car. First was a coat of duraglass filler, rage gold, icing. then the other was just rage gold, icing. both areas have the same ghost effect. after i block out each filler i tend to let it sit for an hour or so to make sure its had some time to cure before skimming on the next. all done in 70-80 degree shop temp.

anyone have any ideas what my problem might be? i figured it would be filler shrinking into gaps between welds because thats what the ghost image looks similar to, but i make sure to leave no gaps before filler. nobody else has noticed it but its one of those things that pisses you off to no end. i spent a ton of time blocking, priming, letting everything shrink, flow coating, buffing to get a super straight/super smooth panel then to have a ghost line appear where my welds are I am currently in the process of respraying the car a different color and it got to the point where i stripped the doors down just to make sure all of the prior metal work looked proper since i have learned much more about metal work over the last year than i did when i started working on this car last winter

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Old 01-06-2011, 09:45 PM
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what is your process after your filler work is done, what primer are you using, how long do you wait for it to cure, etc?
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Old 01-06-2011, 10:08 PM
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Quote:
Originally Posted by mitmaks
what is your process after your filler work is done, what primer are you using, how long do you wait for it to cure, etc?
ppg k38. medium coats, 20 minutes flash time between, 2-3 coats. shop temp is roughly 70ish degrees always (during winter). sits overnight, knock the surface down with 180 and let sit another day to allow solvent to escape. finish blocking with 180, re-prime. let sit overnight, knock the surface with 320 then i let it sit like that until im ready for final block/paint, usually a few days minimum since i work on my personal stuff whenever i have free time. no issues with sand scratches, feather edges or anything else. just faint ghost spots where the welds are. if the panels were not blocked and buffed you probably wouldn't even notice, but on a cut and buffed panel it stands out to me
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Old 01-06-2011, 10:20 PM
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Are you using sealer before paint? I'd let filler primer sit longer (like a month or more) to let it cure real good)
Some guys recommend using lead on welded seams. Eastwood sells lead DYI kits.
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Old 01-06-2011, 10:54 PM
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i might give the lead a try on some scrap stuff at the shop. something i was always curious about anyway. i seal everything i shoot. its just the way i do it since 95% of my work is collision work and that is almost always sealed before base
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Old 01-07-2011, 12:42 AM
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What kind of car and where-area wise- are these patches located? I am thinking the metal may be shrinking-expanding at different rates than the stock metal. Cold roll metal is supposed to have a "grain" to it and may be the problem. Thickness and tensile strength? I am not an expert by any means, I have been to a few classes by Winfield, and he has mentioned that these things can make a difference. Personally, I would think a skim coat and a few coats of primer would have hid this, but like I say, I am no expert.
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Old 01-07-2011, 07:12 AM
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expansion from heat is the only thing i can logically think of causing the issue. car is an 04 vw gti. I actually cut my patch panels from a spare vw oem hood that i had at the shop so i know its all the same material. and for expansion i figured the patch that has the coat of duraglass over it wouldn't be an issue but it didn't make a difference.

Not my car (no pics of when i did mine), but i did the same job. shaved the door handle pockets. also shaved the handle completely on the hatch but that was just a 3"x5" rectangle opening

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Old 01-07-2011, 08:28 AM
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If the patch was MIG welded, that is the problem, imo. The MIG weld is very hard compared to the surrounding metal. Expansion/contraction rates are different.

TIG welded panels won't exhibit this problem.
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Old 01-07-2011, 08:53 AM
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Very interested in the answer to this.

If mig welded patches will always be visible, I need to send my car to the crusher....
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Old 01-07-2011, 08:58 AM
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Dang near every patch panel installed has been MIG welded in place. If that is the problem then there are hundreds of thousands of cars running around with this problem. Your problem is not caused by MIG welding .

Vince
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Old 01-07-2011, 09:22 AM
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Your problem is that youíre using a butt weld. They have their uses such as doglegs and pillar posts, but are not the best choice all around. Because metal flexes it tends to bend at the weakest joints. I use an overlap weld without flanging. It provides a stronger weld hold without flex fatigue associated as evidenced with a butt weld.

Iíve provided two photos of an Acura I sectioned a quarter panel on last week.

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Old 01-07-2011, 09:46 AM
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Quote:
Originally Posted by 302 Z28
Dang near every patch panel installed has been MIG welded in place. If that is the problem then there are hundreds of thousands of cars running around with this problem. Your problem is not caused by MIG welding .

Vince
All MIG welds are not the same........a lot depends on the quality of the wire, the heat settings, etc.
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Old 01-07-2011, 09:53 AM
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Quote:
Originally Posted by mitmaks
Some guys recommend using lead on welded seams. Eastwood sells lead DYI kits.
Your not going to get away with leading todays sheetmetal!
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Old 01-07-2011, 10:11 AM
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I've heard of this complaint from other people before. From what I've heard it's usually appears in the sun when it get hot and the weld and the panel expand at different rates. I hope my current project doesn't have this problem, but I'm doing the body work just like you describe.

My friend replaced the rear quarters on his '70 Firebird and has the same problem.
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Old 01-07-2011, 11:31 AM
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Quote:
Originally Posted by cjperotti
Your problem is that youíre using a butt weld. They have their uses such as doglegs and pillar posts, but are not the best choice all around. Because metal flexes it tends to bend at the weakest joints. I use an overlap weld without flanging. It provides a stronger weld hold without flex fatigue associated as evidenced with a butt weld.

Iíve provided two photos of an Acura I sectioned a quarter panel on last week.

for me to overlap a patch panel for the door handle it would have to overlap on the outside of the door, not the backside. not sure which way you overlap. the pocket has to stay there, cant be cut out because the inner handle/latch assembly is built to work with the pocket in the sheet metal. if i overlapped on the outside i beleive the area would be too high for me to be able to make the handle work proerly. the patch is welded in flush with the door skin but i also drilled some holes in the pocket from inside the door so shoot rust fighter in there for protection.
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