We spot welded mine, so I cannot contribute to your query.

 

Did yoh do the one piece or half pans? As far as i know most people spot weld 1 piece floors.

 

1 piece...

 

Spot weld and used the pieces and now wished i used the one piece

 

I lap and plug welded mine. Punched holes down the rocker side of the pan and the tunnel side then set it in there. Sheet metal screwed it all together and plug welded up the holes. Then I stitch welded the seam between the plug welds together *still have to finish that. ran out of weld gas*. I'll eventually weld the underside of the pan to the tunnel also. Have pix in my link below.

It was much easier to have the single pan set in and level that way compared to lining up the pieces for a butt weld. Also, if I burned through the tunnel I had a lot more material to work with/weld to around that area. To me, and this may just be a matter of opinion, a plug weld that then has a the seam welded is a bit stronger vs just butt welding two next to each other. Honestly do not care what it looks like under carpet and a seam on the underside does not bother me. I'm building a driver, not a show car.

 

To answer your question, most people will lap weld floor pans because it will be under the carpet (inside) and unseen or covered by undercoating on the outside. It's far less effort to lap weld than butt weld. You will see butt welding when you want to make a patch invisible.
As a side note, a lap weld will leave the metal the same thickness (except where it is stacked) while if you are not careful on a butt weld you might grind/sand too much of the weld area and make the metal thinner in that area.
A lap weld is easier to make stronger while a butt weld is easier to make weaker.

 

A butt weld will not trap moisture between the layers and rust like an overlap will.
An overlapping weld is usually faster and requires less skill.

You can overlap and tack weld both sides, then run a body saw or cut off wheel or even a plasma cutter right down the middle of the overlap and have the gap you need to make a butt weld, they even make special clamps to hold it in place.
I would rather have a butt weld with none of the welds ground down than an overlapping weld with goo sprayed over it by the guy that wants to hide it.


If the car matters use a but weld and leave the overlapping spot welded seams where the factory put them in the first place.

 

That's how it is, IMO

 

If you mean replacing a few toe panels or rear seat footwells, yes, a well performed lap weld is stronger than a butt weld. It is also much faster because you don't have to trim and fit and grind them perfectly. You do twice the welding because you should weld the lap inside and outside.

 

I am a union sheet metal worker so I have alot of experience welding thin gauge metal. The simple answer is that over lapping the metal helps take the heat away. It doesnt matter how good a welder you are sheet metal will twist when heated. Butt welds in sheet metal can be done however they take a very long time to make the almost unnoticable. However you can use a pexto roll forming machine that will jog the patch panel to take your heat but only will overlap minimally. Now that being said if I were doing a floor in a mustang ,it has been quite a few years, I would and have done it like someone else said and punch holes and replug weld. Then seam seal and be on your way. If doing a patch on the body I would jog the patch then stitch weld the fill sand prime paint. Let the criticism start now.

 

.... I would and have done it like someone else said and punch holes and replug weld. Then seam seal and be on your way.....

Makes me feel better about mine! If that's good enough for a guy who does it for a living... it's good enough for me.

 

Well, I can see the next generation of classic mustang owners bitching about how the "Previous owner" jacked up the car with overlapping welds and covered them with "Goo"!

Do you really think they have discussions like this over on a GT40 forum or on some of the high end British cars? Why do we insist on saying it's "OK" to do a hack job on a mustang?

 

Ok so the goo you are referring to is on you car now from Ford. These cars are not gt40 s or high British cars the are high production cheap cars. Look at how Ford built them I.e. cowl vents. If done properly with a lap of less than an inch then seam seal then undercoat car is as good or better than New. If you want it to be jewellery then by all mean sit there for days welding 1" welds at a time to keep from twisting. If you want a sound strong clean factory looking install try it my way.

 

I decided a long time ago to do the one piece floor just was wondering this.

 

I don't think this really applies to the one piece pan, just the patches.
Simple enough to me. Lappping is a heck of a lot easier but a bit cheesy. If you butt weld you can make the repairs about invisible and much less prone to long term rusting. That said, pan patches are a pain. I have to admit I used the patches and did my best to butt everything but there are some laps. I hate to see crappy welding on anything and work with it in mind that I wouldn't want someone else looking at such stuff later on and thinking "what jackass did this?" If I had to do it over I'd use the one piece pan and spot it in like the factory did.

 

I don't think this really applies to the one piece pan, just the patches.

Exactly. The 1-piece uses the same hems as the factory piece, and can be spot or rose welded in exactly the same places.

If I had to do it over I'd use the one piece pan and spot it in like the factory did.

Me too. The 1-piece is actually less work than a pair of the old full-length pans, and the results are like new.

 

I agree with anotherhassel. Ok, if you have HenryFordII's or Carrol Shelby's personal mustang, sure go ahead and throw a $million at the car. But if its a GT or a T or a modest 2V coupe, you can build a very nice car without getting carried away. The dirty little secret about this hobby is that you'll never get your money back out of even a "street" level restoration. I admire the VMFers that have showroom perfect cars that collect trophies. God bless'em. I'd probably never take it out of the garage.

 

Wow, there have been dozens of lap vs. butt conversations on this forum, but I have to say this is one of the most provocative. I had my mind set on butt welds because I thought the same thing as many others regarding it being less prone to future rust and less detectable as a repair. However, some very good points have been made for lap welding and I am now seriously considering it for my C code coupe. The kicker for me is that the car will rarely see a wet road and the seam sealer / undercoating should do an exceptional job of keeping moisture out anyway. I can't see how a buyer would scrutinize it in the future. I think in my region, any buyer would jump at the chance to buy a solid car without care for the technique used to get it there. Solid is solid and represents a giant leap forward in terms of the car's condition any way you look at it. I would buy a car with lap welds tomorrow and not curse out the previous owner. In fact, my convertible has lap welds in the floor pans which I had paid to have done at a shop years ago and I'm not disappointed with them at all. In fact, the way they're done you can hardly see them.

 

I don't consider using lapped seams for patches "hack job". If the welds are good, the joints are tight, and they are properly sealed, their function will be good as new. However, if appearance matters, then you must butt weld.

The debate seems more about what one "should" prefer, and you can never settle that one. One guy wants functional and "decent" while another guy wants imperceivably repaired. Neither is wrong just as blue is no more wrong than white.

I chose to use butt welds on my floor patches (eight, in all) so that from below, they were invisible. It's what I wanted. It may not be what you want, but that doesn't make either of us "wrong".

Now, if right and wrong are defined by "how Henry did it", then you have a different discussion. However, Henry did not install repair panels, so...

 

I don't consider using lapped seams for patches "hack job". If the welds are good, the joints are tight, and they are properly sealed, their function will be good as new. However, if appearance matters, then you must butt weld.

The debate seems more about what one "should" prefer, and you can never settle that one. One guy wants functional and "decent" while another guy wants imperceivably repaired. Neither is wrong just as blue is no more wrong than white.

I chose to use butt welds on my floor patches (eight, in all) so that from below, they were invisible. It's what I wanted. It may not be what you want, but that doesn't make either of us "wrong".

Now, if right and wrong are defined by "how Henry did it", then you have a different discussion. However, Henry did not install repair panels, so...

BEST answer I've seen yet. Yee-Haw.

 

I have done both on my car. I did right and left side floors (didn't do one piece), and lapped the tunnel. I feel like it's stronger. I don't thin out the metal grinding as much, and technically have two welds holding it together. It is covered by carpet, and if anybody crawled underneath and really looked they could see the seam. I just don't really care. It's a driver, and it was my first real welding job when i was learning. If I was that worried about it... I would have done a one piece.

I do butt welding for cosmetic welding... like when I did some patches on my tail light panel. Doesn't need to be that strong... just free of rust and pretty.

 

Ditto. I'm in the same boat as you. No one I care about is going to be under the car scrutinizing it. With the seam welded properly, seam sealer applied correctly, and under coating sprayed in the right amount I don't see why someone would poo poo the repair. I guess guys likehttp://forums.vintage-mustang.com/members/41804-fstbk.html Fstbk think the way us lap weld guys do things is totally wrong/the cheap hillbilly way. Apparently our cars are botched together pos's. This is why I don't go to car shows anymore. Last thing I need is a guy poking around under my car and criticizing the way my floors are welded in. Jeesh....

 

Wow. So many of you think that your car is not on par with a British car from the 60's? WTF is wrong with you people?

If you plan on using your car at the drag strip or demo derby then I guess it does not matter, but I seriously dont want to hear anyone bitch about someone calling there car "Just a coupe" at a show anymore since you dont feel like your car is worthy of doing things the right way.

Doing things right is not a matter of opinion here guys. If you cant do it, fine..but dont try to justify shoddy work because you cant do it or wont do it.

 

Fstbk, first and foremost I respect your opinion and I'm showing no disrespect here as you have some great knowledge that I have used some of it in the years I've done my coupe and I thank you for that.

But to be brutally honest the bottom line in all this is it is just every ones opinion as to what is right and what is wrong on this subject of repairs and you are trying present your opinion, yes your opinion, as the one and only fact when it clearly is not.

Rust fixed with pop rivets and covered by Bondo and fiberglass, yes, hack job.

I totally agree with you on that kind of fix and I would extremely pissed if I found that in our car.

A properly done and concealed lap weld patch rust repair not so much.

That is my opinion.
Lynn

 

What next...pop rivets & stop signs?

 

Been there, fixed that!!! I personally butt welded the floors in both my 66 coupes because that was the way I was taught at the restoration shop I worked at in Orlando. The reason given was less of a chance for rust to develop in the joints. As far as grinding the metal too thin afterwards, I used a cut-off disk on my grinder to "thin" the welds but not touch the surrounding metal then hit it with a flap disk to finish. It's time consuming compared to lap welding but virtually invisible when done... Just a preference thing in my case.

 

How are lap welds on floors "wrong"?

 

"Adding" lap welds to a part of the car that did not have them is what we are discussing here. we are not discussing the factory overlaps that the cars were built with (with spot welders I might add).

When you weld them you have made a spot for more rust to grow in between the overlap. Even if you use weld through primer or paint (and few people do) it will rust because the weld burns through that coating and will leave a hard weld that rusts really fast. You cannot coat that inside surface and you are only as strong as that first weld.

I get it that it's easier. But welding on a quarter panel is a nightmare on thin reproduction metals. I have a really hard time doing that and really hate it. Fortunately the floor pan material can be thicker than many of the patch panels found elsewhere on the car and can but weld a bit easier.

And with the full floors being available these days you can have a car with a bottom that looks like it was just built for well under a grand in hardware.


Just because you think having two welds is better than a butt weld does not make it so, if you overheat the effected area when welding you have made a wide patch of brittle metal that can and does often crack, have porosity and can add a weak point to the car.
People like to overlap because it requires less skill and they can pull it off, fine. But the reality is where you patch meets the floor it is just as brittle as if you tried to butt weld it and overheated the metals.

So please dont assume that an overlapping weld is going to give you better results due to its nature.

 

"BEST answer I've seen yet. Yee-Haw." Yep. kind of the same thing I said but I'll agree Crash said it better.

 

Well, the original poster asked why people lap weld? Is it 1. stronger, 2. skills or just 3. easier.

1) No
2) Yea, people do worry that butt welding takes more skill
3) Yep, that's the big one

People lap weld because it's easier. Lappers are slackers.

I'm here for you Fstbk!

If I'm looking at buying a car and see lapped floor pans, I figure they cut corners elsewhere also.

 

I butt welded my floor pans. In retrospect, I wasted a lot of time that i didn't need to.

And the hilarious thing is, I could go over your cars (fstbk and fullbasement) and find tons of things I consider half-assed!

 

Should have gone with a fiberglass repair and saved even more time.

 

Fstbk what makes you such an expert on welding or these cars? Do my welding certs and my 4 yr apprenticeship in sheet metal not qualify me? These cars were the Dodge Neon of their ,time cheap secretary cars. Mind you much cooler looking than a Neon but still the same cheap transportation. You compared these cars to a HIGH END British car. Mustang were and arent high end cars. So no my car isnt on the same level there were probably 300,000 cars just like mine. Doing lap welds doesnt mean shoddy work because if it does I know alot of good metal workers that do shoddy work. It just isnt as pretty as a butt weld. If i was restoring my car with the factory red oxide and nothing else then yes butt weld, but most cars were undercoated including yours it sounds like. As far as over heating the metal have you ever taken a torch to metal and heated it? It anneals the metal. It becomes softer and more malleable. Bottom line is your ways isnt right or wrong neither is mine. There is more than one way to skin a cat.