BODY WORK COMING BACK AFTER 6 MONTHS

I have never heard of VPA until today, It is lap weld. I used a flange tool to inset the one piece and lapped the other over it, You guys are the best and I really appreciate your help and advice. I still would like to know how to seal the back of the panels because once they are in place I can't get to them?
 


This video shows the ghost line left behind from a lap weld. Two layers of metal heat up (expand) and cool down (contract) much slower than the one layer on the opposite side of the weld. Enough cooling and heating cycles and you’ll see a ghost line right down the middle of the seam, as the video shows, as your repairs show. BUTT WELDS are your friend.
 
Sounds like a combination of things could lead up to your issues.
I once thought it sounded crazy to remove a whole quarter panel to do patches & mods on it & then have to weld it back on. Welds & patches done in plain sight & out in the open areas of panels are far more critical than welding near and along a seam & bodyline. Welds running parallel with & right near a bodyline are both stiffer & easier to hide less than perfection.
Ghost lines can occur on very solid repairs. Simply thicker or thinner material in an area will expand & contract differently though solid, as will panel bonded areas that are really solid. Saying it again, these same areas in a better chosen spot near the right type of bodyline, such as between a corner bend & another bodyline are so much easier to hide & stay hidden forever.
First up , I'd suggest coupon sized samples of same gauge & type material & do a practice run replicating basically how you've been welding &grinding. Now you can check backside & bend test. Probably need to just back up & reschool yourself accordingly.
Yes, we can't always be perfect on repairs & a dip inwards on a weld is better than it being a high spot that grinds thin & flexes. Better filler on critical area helps. I recently got VPA for the first time in about 25 years. It has similar consistency of jb weld, but stiffer through expansion & contraction, not being an epoxy. Good improvement for shadow prone areas. Don Hutton also mentioned USC carbo fill , which has carbon fiber strands as an option for bad spots. Haven't tried yet as would have to mail order.

EDIT:: you said lap weld as I was typing. I'll be blunt. If you were my grown son. I would spank you about now. BAD......... Butt welds only or it's your butt.:oops: Out in the open , they WILL shadow every time.
 
JC Daniel said:
I have never heard of VPA until today, It is lap weld. I used a flange tool to inset the one piece and lapped the other over it, You guys are the best and I really appreciate your help and advice. I still would like to know how to seal the back of the panels because once they are in place I can't get to them?
Click to expand...

Sealing the backside can be done with cavity wax and a extended nozzle wand.

Shine gives great advice but in this case I will slightly disagree. I wouldn't get too hung up on using Vette panel adhesive on anything other than fiberglass and SMC. If you are working with metal panels, either aluminum or steel, and use filler properly, give it a few hours after applying, and before priming, shrinkage is going to be minimal. If you are in a rush that's when you get shrinkage. But if you are in a rush you wouldn't be using VPA anyways. If you aren't doing high end stuff, it's not worth the extra work that's required. Body filler shrinkage shows up as sand scratches anyways, not even shrinkage over the entire repair. My Dad always referred to the K.I.S.S. principle.:) As you are learning and gaining experience just keep it simple. Concentrate on learning the techniques and using products correctly. Read the TDS sheets of all the products you use.
As for butt welds, they should almost always be used when patching exterior panels. Lap welds and plug welds do have their place, but usually in structural areas and areas not visible (meaning exterior body panels).
Some essentials for succesful butt welds, most important is good panel fit. Get good fit makes butt welding much easier. When welding always spot/tack skipping around until you have the panel attached. Then continue spotting/tacking skipping around until it is fully welded. Connect the dots so to speak. You never want to do extended beads on a butt welded panel. Placement of the seam is important too. Middle of a large flat area makes it more difficult than if your seam is just below a body line.
 
It is indeed a ghost line showing up, I had no idea not to lap weld exterior panels. I was taught by my cousin the lap procedure years ago and thought that was the only way to do panels, I can say that I really appreciate all the help and comments even the spank my butt comment because it shows how bad I messed up. I have learned everything I know on this forum and can say you guys are the best.
 
I would agree with others here. Lap welds are definitely easier but not the best choice for patch panels. A good butt weld will be a consistent thickness and much less prone to ghosting.

One advantage we hobbiests often have is the ability to let a repair sit for a few months after roughing it in. That allows most of the shrinkage and potential ghosting to be eliminated. I once read that 90% of the shrinkage occurs in the 90 days after mudding a panel. Not sure how accurate that really is but this is why top notch body men do everything they can to limit the amount of filler on a panel. Even more importantly, limiting the amount of primer surfacer. This alone is one of the reasons I love using epoxy instead of 2K primer surfacer. Shrinkage is minimalized.

John
 
I figured everyone could use a laugh on the spank your butt comment, but no need to administer punishment. Your getting your own punishment re-doing things.

I encourage anyone that has a lot to learn to do some back reading on various subjects here . It takes time, but there is a lot of info here from over the years, many times in a seemingly unrelated thread, that can save a lot of heartache & grief. Robert (MP&C) has all sorts of good info over the years here & on other forums to learn from. I've probably forgotten more of what I've learned off him than some people that weld sheet metal will ever know.:rolleyes:

A lot of misinformation on tv & internet. I respect Stacy David for helping start the car show thing, but I saw him showing lap joints as an easy way to patch without mention of shadowing or a place for backside rust to start. Lap joints not only shadow the paint, but they can also collect morning dew at a different rate, giving it away. 78 to 87 el camino license plate pockets being filled in without cutting out are a super common one I've personally seen one time too many. A layer of vette panel adhesive or other specialty filler could help such a situation, but not eliminate it without being stupid thick.
 
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i use VPA because it is very stable when cured . rock hard and so far i've had no shrinkage or swelling with it. it performs much like evercoat epoxy hybrid does. lightweight fillers are soft and tend to suck up solvents and shrink and swell .
one of the worst fillers made is kitty hair or duraglass . worst mapping you will see in the sun. outside it will look horrible , take it in and let it cool and the mapping goes away .
but to each his own. on old indian once told me " what there when start be there when done "
 
Hey John Long don't you live in Chattanooga TN? If so I may stop by sometime if I get to visit my son in Cleveland TN.
 
The weird thing to me about blaming it on a flanged lap is that the factory does that all the time, and their seams don't show.
 
Not on patch panels, no, but on vehicles with unisides, when partial replacing we have to do a butt joint with insert, and that is double metal. I have to admit that there's not too many chances to reinspect daily drivers, people tend to trade them off before we see them again. But we've never had a comeback for anything like that.
 
I personally butt weld all my patches but have read that using panel bond adhesive when doing lap joints is better than welding them. The thinking goes that there will be no pockets of air (gaps) in the lap joint and hence no movement due to temperature changes.

Anybody have experience with this method?
 
'68 Coronet R/T said:
I personally butt weld all my patches but have read that using panel bond adhesive when doing lap joints is better than welding them. The thinking goes that there will be no pockets of air (gaps) in the lap joint and hence no movement due to temperature changes.

Anybody have experience with this method?
Click to expand...

It's not about air it is the metal itself expanding and contracting in hot and cold temps. Because of the two layers of metal next to a single layer the expansion and contraction is different. Hence the visibility of a seam. Look at the video again that Robert posted.

Butt joint with an insert isn't really a lap though Crash. Broad area behind the weld. Even on both sides of the weld. When a lap shows its always at the seam where the new panel meets the start of the offset area on the old panel. Even fully welded that is where it will show because 2 layers are up against one layer. And it's welded. If it wasn't welded then the metal on the 2 layer side would expand on the path of least resistance (meaning down and away) and not show. That is one reason why spot welded laps don't show on OEM's And most OEM laps are done with an exposed seam, usually in a fairly narrow area. If the OEM's lapped in repair panels the seam would show just like they do for us.
 
Also, the depth of the flange on OEM is enough for another layer of metal-----or lead----and most lap welding guys are happy if the seam is level.
 
I wonder if MIG brazing a lap joint is different. The OEM flanged lap joints that I have seen (that didn't have a 'ditch' for lead') were all done with bronze filler material. At the time I found it pretty amazing how nice the were able to make them in a production environment no filler, just the bronze seam.
 
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