[lintmann]

So I have three areas of floor in my 70 GTO that need work, one is a large area under the drivers foot well, next is a small area under the passenger rear seat and last is about 3/4 of the trunk floor.

I started with the smallest which was an area about a foot square under the passenger rear seat and butt welded this one and it came out quite nice. Now I'm starting on the trunk floor one but before I started I figured I'd look into some youtube videos for any tips or tricks that might help me along. What I'm seeing so far is that they are lap welded with about a 1/2" over lap....

My intent of this car is to have really nice body-on restored driver so my question is, is the overlap weld a common and acceptable practice or does it really need to be butt welded??? The same question also applies to the drivers floor area that I will have to replace too.

Thanks, I appreciate your thoughts!

[RocktimusPryme]

Some people do it for the cleanest possible look, but butt welding is a waste of time IMO. The floor seams are overlapped from the factory and pinch welded in a bunch of places.

Personally I like to use a flanging tool to make the hole I cut out flanged. Then punch holes in the patch. Do a bunch of rosette welds. Seam seal and call it a day. Opinions will vary. But when it’s common practice to overlap/knock down the weld/add filler on exterior panels……why would you want to go nuts with something you are going to put carpet over anyway.

[rustedgoat]

Overlapped panels with todays materials could easily last outlast other parts of the car and would be fine on a general transportation or non collector cars.

If I'm looking at a car and see a bunch of obvious patches under the car I see it as a red flag that someone took shortcuts on the resto. It's just unnecessary, If your doing the work yourself the floor is a great place to do butt welds on heavier gauge metal, even if its not perfect its not as obvious as a raised patch. The extra time put in to do an undetectable repair is well worth not having to explain the patches and why they were repaired that way.

[Entropy11]

I think it’s all personal preference but your time invested now does impact future sales. If I see lap welded patch panels I’m usually thinking it’s a diy repair or a budget “restoration”. If it’s on a car I’m going to sink some money into in other places, that would be the first thing I’d cut out and butt weld correctly. In my mind there’s no way to lap weld patches and not worry about future corrosion when compared to butt welding. If you already can do a nice job butt welding and have other areas to do, then it’s just a matter of your own time to make it a “non-issue” when selling it down the road. Like I said though… all personal preference!

I did about 3/4 of the trunk floor in my ‘68 and went the butt welded route. I have a write up on it here somewhere with a bunch of pics.

[RocktimusPryme]

Like I said, opinions will vary. I knew this one would be a can of worms.

I’m not trying to change anyone’s mind but I gotta say though I don’t understand the resale value aspect. You can still see a buttweld underneath a car. So it’s not like it’s hidden. And a weld is a corrosion weak point no matter how you do it when left to its own devices. So you are still reliant on coating it. And from under the car you often don’t have access to grind the whole thing flat because of the frame.

I’m not saying I haven’t seen hack jobs. But if the floor was overlapped (especially flanged the way I like to do it) and is coated with weld through primer, then seam sealer then paint. With a buttweld in a perfect world you go over it with fiberglass before paint but you ussually don’t have access to that under the car.

I don’t see how one is better than the other from corrosion standpoint I’m just happy someone got rid of the rust before I had to deal with it. But I also don’t buy 80,000 dollar cars.

If the concern is making it all look factory under the car then just put a hole new floor in at that point.

Honestly I would be 100% more concerned about the longevity of a welded panel repair on a work truck than I would about a garage kept hobby car. No matter what method was used. With a classic car that get treated like a favored child there is different stuff I would rather stress about.

[VCho455]

Originally Posted by RocktimusPryme

Some people do it for the cleanest possible look, but butt welding is a waste of time IMO. The floor seams are overlapped from the factory and pinch welded in a bunch of places.

Personally I like to use a flanging tool to make the hole I cut out flanged. Then punch holes in the patch. Do a bunch of rosette welds. Seam seal and call it a day. Opinions will vary. But when it’s common practice to overlap/knock down the weld/add filler on exterior panels……why would you want to go nuts with something you are going to put carpet over anyway.

Warning hijack in progress!

What is your preferred flanging tool?

[RocktimusPryme]

Originally Posted by VCho455

Warning hijack in progress!

What is your preferred flanging tool?

100% honestly, I have a cheap harbor freight one which works, but it could be stronger. Sometimes I hit the button twice before I reposition.

I would like to buy a new one. I would also like a tool with a hole punch that let you get a little more depth from the edge as needed than the one I have.

While I unfortunately don't have a great answer for you, I have found that Astro Pneumatic air tools generally strike the best balance between affordability and performance.

[Goatracer1]

How long are you going to keep the car? If its a long time do it the way that YOU can accept. If you are going to sell it soon butt weld them.

[Entropy11]

I don’t think it’s really a can of worms it’s just differing opinions. Everybody has one.

In my mind if you’re butt welding then you’re going through that added labor with the intent of grinding it flat and not seeing the repair at all. It’s a waste to go through the added labor of butt welding only to leave your weld bead “as-is” and unfinished. At that point you may as well just flange it or save even more time and just overlay it if you plan to trust seam sealer and filler.

Yes, any weld could be a future corrosion point as compared to solid sheet metal but that doesn’t mean you shouldn’t weld or trust your welds if done correctly. If I’m doing a patch I’m butt welding the entire perimeter, grinding down my weld bead to a point it disappears, reshaping as necessary, then prepping it for epoxy primer and priming it. I’m far from perfect but I do enjoy taking my time to do a quality repair nobody will ever see. That’s half the fun to me. After 2 coats of epoxy I better be at or at least close to the point of not seeing or really catching a fingernail on the repair. Fiberglass??? Again, why go through the hassle of butt welding if you have to half-ass it with fiberglass and thick layers of filler? It’s defeating the purpose.

The potential for corrosion should be a fraction with butt versus flanged/overlaid. In one hand you have a completely solid repair and in the other you have 2 pieces of steel sitting on top of each other partially welded together. You’ll always have that added potential for corrosion between those two layers because you’ll never (ever) have complete coatings on those 2 surfaces facing each other. If you do believe in weld-thru primer doing anything for you (right next to welds that are easily over 3000°F), you’re still never getting a secondary epoxy coating over those surfaces stuck together. You’re also always going to be stressing the repair with that method due to uneven thermal expansion/contraction. Every heat/cool cycle you’re going to be inviting cracks in your seam sealer, primers, coatings… inviting water, humidity, and ultimately, corrosion.

If I’m repairing some small holes in the heel area of a driver foot well, I’d rather go through the hassle of a butt weld as opposed to swapping in a while new front half of the floor! Again, we all have our opinions and nobody can really tell anybody else what’s best for them. It all comes down to what you feel is an acceptable repair for you versus the effort you’d like to put in 👍

[lintmann]

Thanks Guys, that's all great advice and food for thought. I'm going down the road of butt welding my trunk floor patch but RocktimusPryme has me thinking that flange welding might be the way to go with the drivers foot well floor patch.

My thoughts are that it might be much more difficult and time consuming to butt weld this patch because of all the curves. If I flange the panel and set it on the carpet side then the road side should be flush and easy to finish. I'm not concerned with corrosion because the car already has several factory welds with no primer between the panels, also it's not a daily driver.

[LKLusza]

I did like RockimusPryme said back when I had a '37 Chevy street rod. I was able to use a "Bitchin'" brand floorboard kit, but the process was the same. The panels were designed w/a flanged, overlapping joint and holes for rosette welds. The panels were held together with self-tapping screws that were removed and the holes filled in with weld when done.
After that it was seam sealer and primer time. The finished product was great looking and strong as can be. I also think the rosette weld procedure is easier and less time consuming.

[RocktimusPryme]

Originally Posted by LKLusza

I did like RockimusPryme said back when I had a '37 Chevy street rod. I was able to use a "Bitchin'" brand floorboard kit, but the process was the same. The panels were designed w/a flanged, overlapping joint and holes for rosette welds. The panels were held together with self-tapping screws that were removed and the holes filled in with weld when done.
After that it was seam sealer and primer time. The finished product was great looking and strong as can be. I also think the rosette weld procedure is easier and less time consuming.
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I use Cleco's left over from A&P school sheet metal training instead of self tapping screws, but same concept.

Honestly, I think the best advice in this thread has been to do what you are going to be able to accept.

There is a time and place for all sorts of techniques. If the panel area has a boatload of beads rolled in it, maybe flanging wont work well. On the other hand, if you arent going to be able to grind flat on the bottom because the frame is in the way, maybe a butt weld is a waste since you cant make it pretty.