Roof patch causing warp / oil canning

[88Stanger]

Thanks for the detailed help here !!! MP&C you could almost write a book with your great detail and Pics! Great info.

[ItWillBeSlow]

Originally Posted by 88Stanger

Thanks for the detailed help here !!! MP&C you could almost write a book with your great detail and Pics! Great info.

I 2nd that! Much to be learned here and it is very cool people are willing to take the time to hand out free advice

[MP&C]

Originally Posted by ItWillBeSlow

- Can anyone elaborate more on the ghost lines, and why these are a risk? I planned to sand/grind all the joints, skim coat with bondo, epoxy, high build, then paint. Im not understanding how this patch would be different after it is prepped like the rest of the cab.

This video shows a reflection in the rear tailgate of a 54 wagon, the owner had done a nice job of restoring it, the car was neat as a pin. The only flaw was that he had used a stepped/flanged repair on the patch used on the lower tailgate skin. You can see the exact location of the seam, despite the filler used, and you can even pick out the screw holes that were plug welded closed. The other patches on the car were all butt welded with no discernable ghosting. I was given permission to take and show the video in hopes that others could learn from it and take prevention steps.


https://www.youtube.com/watch?v=OGhFEfVqxb0


This occurs because you have two thicknesses of metal to one side of the weld, and a single thickness to the other side. Two thicknesses will take longer to heat up when exposed to sunlight (think car show) and longer to cool down that evening than the single thickness on the other side of the weld. This differing expansion and contraction rate will cause a ghost line right at the seam, showing exactly where the repair was made. So when I respond to various patch panel welding questions, this is also why I stress to grind welds on both front AND rear of the panel. We need the panel thickness consistent to help eliminate the cause of ghosting.

[nsb29]

I don’t think anyone is better at this than Robert and what he is telling you is 100% correct. In your situation and neither one of us having the skills that Robert has I still think metal bond is the way to go. I don’t think it matters whether it’s a round hole or a square hole just keep it to a minimum, if you use C clamps to hold your backer in place just don’t make them so tight you squeeze all of the adhesive out and then do the same with the patch it should equal out. The one thing I believe in 100% is to use a polyester high build like slick sand which has zero shrinkage as opposed to a 2K primer which will minimize if not completely stop any ghosting

[ItWillBeSlow]

Originally Posted by nsb29

I don’t think anyone is better at this than Robert and what he is telling you is 100% correct. In your situation and neither one of us having the skills that Robert has I still think metal bond is the way to go. I don’t think it matters whether it’s a round hole or a square hole just keep it to a minimum, if you use C clamps to hold your backer in place just don’t make them so tight you squeeze all of the adhesive out and then do the same with the patch it should equal out. The one thing I believe in 100% is to use a polyester high build like slick sand which has zero shrinkage as opposed to a 2K primer which will minimize if not completely stop any ghosting

Thanks for the response and I do agree the more I learn. As stated earlier by someone else, if a small ghost line in this area is my worst issue here, I will consider this more than successful.

When I think about the best way to do this, I believe it would be best to space the backer to allow the metal bond some room to fill and not completely squeeze out. I made a diagram of this below.

Please keep the comments and experience coming, I plan to tackle this within the next week or so and would like to iron out a couple of these details. I think the backer strips will be about 1/3" thick to properly attach the roof panel and provide a lip for the patch. If there are other thoughts please share.

[HAULIN' IT]

I'll add a bit more to the discussion.
First a question for Robert...Was the tailgate you showed in the video for sure mig welded solid? Ive seen some things like that before (glued, Lenco spotwelded along the edge & some tacked every couple inches that you could see EVERY weld & gap), but never a fully welded seam to that degree of ghosting. What I have seen several times (which if it was done on a big long seam like that, I can imagine it looking very similar) is the weld has a side (or both sides) with a real bad "undercut" left along the weld. An example would be a guy closes up the gas filler hole in the truck cab corner by laying a patch in behind & welding around the hole. Once finished, the INSIDE edge of the weld shows the "step" after some time in the sun because of the drop-off...the outside does not because it was able to be easily ground smooth with the original metal. One very good reason for your insistence of the butt-welding panels. Like you mention, you go to a car event on a hot day &/or as the sun is going down & dew is starting to set in...you see some interesting things!

To add to what Robert said about the question about how/why the ghosting...at least with using panel bond, I think there is another factor, but really all the same reason Robert stated & that is, simply the difference in the makeup of the items heating, cooling, ect at different paces & react differently to heat, cool cycles...we have a sharp cut metal edge of the original panel, we have a sharp cut metal edge of the patch...in between/around the edge is a very good insulating item (somewhat like a plastic material). See where Im going?

So what to do to minimize the ghosting? I have found a few things that go the right direction to minimizing the chances. First, you taper off the upper square edge of the original metal & the patch...similar to what doing drywall would look like. Second, As I mentioned earlier, I prefer the Fusor 208. It dries harder & is more solid than the "panel adhesive" products like 108, 110 ect. which is really more a metal glue intended for flanges which stays slightly "gummy" & can never really be feathered out.
This part is going to make Robert go take a blood pressure pill, but as I stated earlier...Im a realist. Body filler is really a friend to nearly everyone until they hone skills in like Robert has. So here it goes...Don't try to make it "too good". Yep I said it! What Im getting at is this. I promise you if you work real hard & make your pieces real close to flush not needing/having much room for "glop on top of it" it WILL ghost line on you. If you have room for a uniform coat of hard base filler like Duraglas, all-metal, something of "insulation" on top of your patch, the odds are much reduced you see a line. Just like nsb stated, a polyester primer is also my choice (Clausen Sandy or Rust Defender is my pick). I distinctly remember one of the Roofs I did years ago on an Impala. The local department had a car & wanted to make it an undercover detective's car. It started out Black & White with lights, antennas, ect. & ended up all White with pinstripes, mudflaps & full wheel covers...looked just like grand paps ride! I grabbed a pick hammer, tapped down the mess the last guy made drilling & mounting the stuff & glued plates over a couple holes on the roof, one on the trunk & an oval on the post from the spot light. That car was back in the shop for a deer hit & someone backed into it years later...couldn't find any of those spots, not a flaw to be found years later. It sat outside everyday, but it was White also. What Im getting at is: "The Roof was ruined by the guy with the drill", I made it better even if it would have shown a ghostline...no one but a trained eye was going to find one if it was there. One of the neat things of over 30 years "practicing" auto body repair...you get to try/see how things work out or dont work out. Lorne

[ItWillBeSlow]

Originally Posted by HAULIN' IT

I'll add a bit more to the discussion.
First a question for Robert...Was the tailgate you showed in the video for sure mig welded solid? Ive seen some things like that before (glued, Lenco spotwelded along the edge & some tacked every couple inches that you could see EVERY weld & gap), but never a fully welded seam to that degree of ghosting. What I have seen several times (which if it was done on a big long seam like that, I can imagine it looking very similar) is the weld has a side (or both sides) with a real bad "undercut" left along the weld. An example would be a guy closes up the gas filler hole in the truck cab corner by laying a patch in behind & welding around the hole. Once finished, the INSIDE edge of the weld shows the "step" after some time in the sun because of the drop-off...the outside does not because it was able to be easily ground smooth with the original metal. One very good reason for your insistence of the butt-welding panels. Like you mention, you go to a car event on a hot day &/or as the sun is going down & dew is starting to set in...you see some interesting things!

To add to what Robert said about the question about how/why the ghosting...at least with using panel bond, I think there is another factor, but really all the same reason Robert stated & that is, simply the difference in the makeup of the items heating, cooling, ect at different paces & react differently to heat, cool cycles...we have a sharp cut metal edge of the original panel, we have a sharp cut metal edge of the patch...in between/around the edge is a very good insulating item (somewhat like a plastic material). See where Im going?

So what to do to minimize the ghosting? I have found a few things that go the right direction to minimizing the chances. First, you taper off the upper square edge of the original metal & the patch...similar to what doing drywall would look like. Second, As I mentioned earlier, I prefer the Fusor 208. It dries harder & is more solid than the "panel adhesive" products like 108, 110 ect. which is really more a metal glue intended for flanges which stays slightly "gummy" & can never really be feathered out.
This part is going to make Robert go take a blood pressure pill, but as I stated earlier...Im a realist. Body filler is really a friend to nearly everyone until they hone skills in like Robert has. So here it goes...Don't try to make it "too good". Yep I said it! What Im getting at is this. I promise you if you work real hard & make your pieces real close to flush not needing/having much room for "glop on top of it" it WILL ghost line on you. If you have room for a uniform coat of hard base filler like Duraglas, all-metal, something of "insulation" on top of your patch, the odds are much reduced you see a line. Just like nsb stated, a polyester primer is also my choice (Clausen Sandy or Rust Defender is my pick). I distinctly remember one of the Roofs I did years ago on an Impala. The local department had a car & wanted to make it an undercover detective's car. It started out Black & White with lights, antennas, ect. & ended up all White with pinstripes, mudflaps & full wheel covers...looked just like grand paps ride! I grabbed a pick hammer, tapped down the mess the last guy made drilling & mounting the stuff & glued plates over a couple holes on the roof, one on the trunk & an oval on the post from the spot light. That car was back in the shop for a deer hit & someone backed into it years later...couldn't find any of those spots, not a flaw to be found years later. It sat outside everyday, but it was White also. What Im getting at is: "The Roof was ruined by the guy with the drill", I made it better even if it would have shown a ghostline...no one but a trained eye was going to find one if it was there. One of the neat things of over 30 years "practicing" auto body repair...you get to try/see how things work out or dont work out. Lorne

Thanks. I am definitely not chasing perfection with this repair, and I am already making the truck 3x nicer than I ever intended to. I am honestly more concerned of a future crack or failure with the metal bond, than having a ghost line. This is an area that's hard to see on a truck anyway, and I would likely forget about it in no time. However, I do want to make sure I am following all reasonable steps to make sure its a durable repair.

Do you have any comments to my sketches above with the backer? My core concern is a small backer strip leaves little surface area for the original roof skin and the patch to all mate together. Do these strips need to be wider? Should I space it down to allow more room for the bond material to fill the void and not squeeze out?