backing strip vs dimple and lap weld

[Harry]

Here's a quick quandry regarding a previous post about patch panel welding. Len recommended putting a backing plate and then butt welding the replacement panel in place. I have used this method before and it works great. I do have a panel crimper tool and was wondering how the crimping method would work as opposed to using the backing plate. To replace a quarter panel, I would crimp the existing metal, fit the new quarter to the existing panel line, plug every 2 inches or so and "butt weld" the gap.

According to the backing plate method, I should fit the backing plate to the existing metal and plug weld in place, fit the new quarter to the existing panel line, plug weld the new panel to the backing plate and butt weld the gap.

Any thoughts or preferences on the 2 different methods? I like the first one as there is only one open gap behind the panel to collect debris. Since it is a resto, I also want to hide this area as well as I can so it doesn't show up when the trunk is open. I am just looking for suggestions about strength, ease of process and any other ideas. Thanks in advance
Harry

[Len]

Lap welding is ok for certain jobs but not good for others. I find that the backing strip method works better than lap welding when the seam runs across a curved panel because it doesn't distort the metal like lap welding. When you lap weld you can easily make the lap too deep or not deep enough OR the bend will cause the need to do more filling or metal work on the panel.

When the backing strip method is done properly there is very little filler needed to hide the seam.

[Harry]

Thanks for the info, Len. I was actually concerned about hiding the backside of the repair since it is a resto and I hate it when there is an unfinished seam on the inside when a quarter has been changed. I guess I can cover the inside, where the backing strip is, with fiberglass and clean it up that way. I really did like that backing strip method the last time I used it.
Harry

[Len]

Yes, with the lap method you get one seam on the backside and with the backing strip you get two. The only way to get away with no seam is to do a straight-up butt weld or to replace the entire quarter instead of using a repair panel.

[68-chevyman]

Most of the time I do a but weld period. I use someone else to hold a copper block on the back side. Hammer and dolly as you go. Grind bolth sides then hammer and dolly some more. Do a few srinks if you have to. The results will be outstanding if you have good acces to the back side that is.

[68-chevyman]

Just wanted to add pic. for an example56