The Stovebolt Site Forums The Shop Area Paint and Body Shop Lap or butt?

I was going to butt weld a new piece in the existing hole, but I'm
thinking that due to the age of the metal, and the # of holes, I better just put a large piece of new metal behind the hole here, and tack it up.

Would you all agree?

The age of the metal doesn't matter, just if it's rusted away or not. If you're closing the (taillight?) hole, and planning on smoothing it over with bondo, then it probably doesn't matter.

But it it was me, I'd butt weld a patch in.

Thanks.Yeah, it's the taillight. That metal is like 1/32", and I'm afraid if I'm not careful, I'll just start blowin holes

If you can get a copper backer behind your joint, that'll keep you from blowing holes in it (to some extent).

A lap weld is more likely to show the seam as a ghost line. Two layers (where the overlap occurs) is going to have a slower expansion rate when heating up (sunlight) and a slower contraction rate when cooling off in the evening than the single layer adjacent to the repair. This difference in expansion rates will cause a ghost line to show exactly where the repair occurred. A butt welded seam that has been planished and dressed afterward will give better results.. Here's a video that shows a ghost line from a lap seam in a tailgate repair.

Alright, you guys sold me

I'll give the butt weld a shot first but cut a piece to have on standby for the plan b lap weld.

Thank you very much for your feedback!!

I've said this here about 1157 times, but on stuff like this you can use J.B. Weld quite successfully and avoid the worry about welding. You can also use silver bearing solder (Harris StayBrite is best). Do the back-up thing you mentioned, let the epoxy cure well and then simply epoxy the replacement piece in there. 40 years ago I got a crack where the roof joins the windshield pillar in mine. Repaired it with J.B. Weld and haven't had a problem.

Thanks, Jon!!

Well, I scrambled before the rain to cut a piece of metal, fit it, prep it, and get some tacks on it before the rain actually began. The rain gave me no warning shot, but I thought you guys might like to see how it went. I still have work to do, but it sure looks better than a gaping hole cut by a shadetree!!

Just a comment: If you clean off the rust from your patch (and the edges of the holes), you'll get a MUCH better quality weld using MIG. If you're using flux core wire instead of solid mig wire, the polarity needs to be reversed and penetration will be deeper, increasing the potential for blowing holes in the metal.

Thanks! I definitely prepped the metal, you'll see it's brighter in the last pic.

I will have to check my welding wire. I got this welder used and, although it works, it's more twitchy than the Lincoln I bought new many years ago.

I was also blowing through initially bc the heat was set too high. I dialed it back and got to a much better place.

Just checked the welder, the polarity is correctly set and the wire is Lincoln L-56 Super Arc MIG wire.

Here's another closeup of it right before the rain started. I had to quickly hit it with some flat black.

Looks very much like my first attempts at welding sheet metal, but not too bad. It'll work.

Robert recommends using a trial weld with a couple pieces of metal before attempting the patch to get the welder set right, but with existing metal that's rust-thinned, that's a bit of a guess. But it would get you close on the welder settings.

I've been away from welding for over 10 years. It's coming back, but thank God this isn't a show truck!

This is also the oldest metal I've ever welded on by far, so, it's yet another learning experience

Would like more info & detail on using the silver solder and JB Weld!

I agree with Kevin, your pieces don’t appear to be clean enough for good strong welds. The edges need to be ground to good solid metal, free of rust and paint (front and back), otherwise the weld is going to draw the contamination into the weld giving you porosity and a weak weld. It will be much easier to weld, your welds will look much better, you’ll get less spatter and it will be a much stronger joint.

Just don’t get carried away and thin the metal too much. Keep at it and you’ll get it!

Thanks guys.

For the remaining holes that are there, I think I'm going to put another piece of metal behind them, to use to build the blobs up. No-one will see the inside piece, and it will help to keep me from burning those holes any bigger. I don't want to have to use a bunch of Bondo there, and I don't want to eat up any more original metal.

Now if it would just stop raining! It's 5/29 and it's 40 degrees out!!

So I'm curious: how would/could that be fixed? Obviously it would have to be resanded and repainted at minimum 😕

As to the blowing holes, don’t be so quick to turn down the heat, I would first adjust to a faster wire feed setting and then adjust the operator to a shorter duration on the trigger pull. A faster, hotter weld tack will give you flatter weld with better penetration. So in essence the quicker on-off of the trigger pull gives you less heat without sacrificing weld penetration. See the “MIG welding tips and tricks” sticky at the top of the page for more Info.

For fixing the tailgate in the video, it is only going to get worse with time and exposure to sunlight (think car shows). It would need to be pulled apart and another patch welded in using a butt weld, unless what is there could be saved by cutting off the excess metal (flange). Then, planish and grind down the welds to get the weld seam as close to panel thickness as you can, for the best possibility of eliminating differing expansion/contraction rates and thus eliminating a return of the ghost line.

Looking at your weld picture above, I think the other part of your blowout situation is the wider gaps in some areas. The tighter you get those gaps, the better. Also explained in the tips thread.

Thanks for the info! I did actually try adjusting the wire speed first, before bumping down the heat. I'll keep at it, though!

Bummer for the guy's car in the vid! That's why in our family, we pretty much stick to the '10 footer' grade of car if it turns out better, well, we'll take it!

Silver bearing solder (like Harris StayBrite) is a fluxable solder (uses an acid flux) and will join not just copper, brass and metals in that family but also ferrous metals. And it will solder them very well and as strong as goat's breath. The benefit is this solder melts at about 450 F, so you won't be warping things or blowing holes in metal, etc and when you're done, you can grind/sand it in the same fashion that lead was once used. It isn't cheap, but no solder sold today is cheap. One of the neatest ways to use this is to get a pair of Vise Grip flange pliers. Use those to make a flange on the piece you're soldering to and then cut the part you're replacing to fit nicely on that flange. Then clean both pieces, add flux (will be like water but acid), heat and solder. When you're finished, mix soda in some water and pour it in/over to neutralize the acid. And in a fraction of the time and a fraction of the irritation/confusion, you're done. Say for example you're replacing the bottom 8 inches of a door skin. Measure and cut, leaving an extra 1 inch for the flange (or whatever size your pliers are), use your pliers to flange the door and then set the new piece on top. Add flux and solder away. With no more heat than you're using, it isn't going to act all funky on you. It will just sit there and behave until you're done.

As for J.B. Weld, I do the same basic thing but if you don't have flange pliers or if the area won't be compatible with those, cut a piece of the same weight metal to be a back-up plate for you. This will go around the inside of the piece you're epoxying to. Let's say you're replacing a radio cut that somebody made a mess out of. You'd clean that up, epoxy the back-up plate behind the cut and let it set. Some of the J.B. Weld will set in 6 to 8 minutes, so keep that in mind. You may want to make 4 back-up pieces if you are working on a square or rectangular piece. That in essence will be your flange. Once that sets, then apply epoxy to the back-up piece and the piece you're attaching as the replacement, get it all aligned correctly and use a piece of masking tape to hold the pieces in place. When that sets, remove the tape, give it 24 hours to fully cure and you can sand the seam just as if you had used Bondo. You can use either of these approaches in either areas subject to stress or areas (like your radio cutout) which see no stress or very little stress. A friend of mine once cut a rear fender in half (top/bottom) and cut another in the same place (one without damage on the bottom), joined both with J.B. Weld and the seam never gave him any problem. It took him two packages of J.B. Weld to do this, but how much does that cost? $6 for a package? That's a lot cheaper and easier than welding and...J.B. Weld will never rust. Besides as I said before it is a heck of a lot easier to grind/sand/finish.

Please don't get me wrong. I was trained as a welder and have done it professionally. Welding is fine, brazing is fine...but it is just like I would expect performing surgery is. The more you do it, the better your work gets.

Below you can see where I repaired the pillar to roof seam on mine 40 years ago using J.B. Weld. This area definitely gets stress and it hasn't gone anywhere since then.

I may try this on my driver door. On the area where it is by the front pillar, the door metal is cracked. I'm wondering if someone pulled on it at some point in order to rip the door open. I've said it before and I'll say it again: this poor truck!!

I would suggest making the hole smoother. And clean all the paint and rust away. Round the corners. Then hammer the edges flat and straight. Then take your patch piece and, if you can hold it from behind, trace the hole on to the patch piece. If you can't reach behind, use a magnet. Then go trim your patch piece. Sneak up to that line and leave a lot of the line there. Test fit, trim a little, test fit, trim a little, repeat. What, you have a car show to go to next week? No, you have plenty of time. If rain is coming, walk away until the rain goes away. In other words, don't rush it. Like any job that isn't rushed, you'll have a better result. Same with when you start welding. Take your time, don't rush it. Check it often to see which way your metal is moving so you can react accordingly.

The silver solder was a great idea and your explanation on how to use it was great! one last(maybe) question about the silver solder, what type of heat source do you use? propane torch for lower heat or acetylene torch? Seems like a lower heat source would be helpful for a beginner, or any other suggestions. Thanks for giving the details!

Appreciate the tips. Thanks!