Spot Weld or Continous Weld

[pbets756]

I am going to be putting a partial floor pan in my new purchase soon. What is the better method, nicely measured spot welds or a continuous weld. I am knowledgeable on warping and if I went with the full weld I would weld-cool weld-cool. What are your thoughts. Thanks Paul

 

[AZ73]

I did weldable primer between the pieces, spot weld. tapped with body hammer to get flat. primer, then seam sealer.

 

[bronconut73]

One of the guys on here screwed his floor pans in. He used a nice even screw pattern. Then he pulled one screw out at a time then weld the screw hole up. It looked nice when he was done.
I wish I had seen that before I did mine.

 

[Fairlane514]

Continuous weld will withstand twisting and stresses better, especially if you are cutting out the old floor and butt welding in the new panel.

 

[allenfahey]

The correct way is to do as AZ73 described. The base metal does not get any holes drilled in it. The panel you put in gets holes drilled and it is spot welded. You don't weld the outside seam at all.

 

[Scoop]

I use both methods on the same patch! Where i'm patching a place i've cut out I do a continuous weld but along the door jambs or to attach to floor supports I drill and spot weld. I use zip screws to keep the patch tight to the existing metal, do my spot and seam welds, remove the screws and fill the screw holes. IMO the screw holes are not big enough to use them as spot welds.

EDIT: Basically I use spot welds where the factory used spot welds and continuous welds where it was a solid panel before.

 

[sp71eb]

So here is my take on spot vs. continuous weld. Cars are spotwelded from the factory for a reason. And the various panels are also designed to move somewhat at those seams. I am by no means a car engineer but I also work on cars daily replacing panels and doing body work. One thing to think about is the HAZ (heat affected zone) around each weld. While welding you are heating that surrounding area and making that surrounding metal hard and brittle. I see lots of patch jobs on rust repair where a continuous weld was made and usually if it is a high stress area you will see a crack right along the weld. For this reason spot welds are better. Think if your weld starts to split in one spot on that continuous weld it will have a path to keep going. I can understand the idea of trying to make it stronger by continuous welding but I don't think that ends up being the end result. The best rule of thumb is spot welds spaced 1.5" apart along the edge of the panel. Also make sure to place spot welds on corners or high stress areas. One place I have noticed is where your welds need to be placed properly is where your e-brake cable bracket is under the floor. I like to put two welds right where it is on the floorboard. Another thing is just let the welds cool naturally. Just keep moving around the panel welding, I like to go every other weld and the come back and get the rest of them. Hope this helps. Sorry for the Article.;D

 

[Jedhead]

Nice bit of practical advice, sp71eb. You would think a solid weld would be better, but your explanation makes perfect sense. I always wondered about that. What's your choice for a quality seam filler?

 

[allenfahey]

What's your choice for a quality seam filler?

THIS is a really good seam sealer. Before you apply it you have to prime and scuff the seam. It requires a special double barrel caulking gun. A decent caulking that doesn't require the special gun that I've recommended before is Lord Fusor EZ800.

 

[sp71eb]

Allenfahey has some good recommendations as he is also in the body industry. I personally use 3M ultrapro 8361 for a single part seam sealer. This works good on interior seams and is cheap, flexible, and won't shrink and crack on you. 8361 requires a special gun but if you get 8300 it is the same stuff but in a tube for a regular caulk gun. On exterior surfaces that will get paint and need a more rigid seam sealer I use Fusor 123EZ which is a 2 part seam sealer. As allenfahey said two part seam sealers require a special gun to apply. Any of the products either of have posted are about the same just different brands and some may not be available at your jobber.

 

[Crawdad]

Great info guys!

 

[nickgp]

We screw our panels down with tek screws, evenly spaced. Once its all down, and tapped down where needed, start by removing every other screw. Take a 3/8 inch drill bit and drill almost all the way thru the top panel. Try not to go into the bottom. No big deal if you do, just involves a bit more grinding for clean up. Alternate where you are putting your spot welds. Once you have those done, do the same with the remaining screws. The Lord Fusor 8000 works great. On the 74 we brushed it with an acid brush dipped in thinner once a bead was laid down. Also used a latex gloved finger to smooth it. This gave us a nice smooth finish which we applied 3m body schuitz inside and the bottom of the tub. This provided a nice, orange peel type texture which is painted body color. Yes, its a ton of work, and a pile o money but the end result is awesome. Funny that many, if not all the so called "restorations" being auctioned/advertised on our site dont do this. Usually, its carpet hiding the crimes beneath!

 

[kbank6]

I am doing my passenger side right now and have used the air punch from Harbor Freight. I thought the hole was a little small so once I figured out were I wanted all the plug welds I ran the air punch over my markes then went through with a 1/4 drill bit. Still used the screws to hold it all down but just made sure I had good plug holes.

 

[pbets756]

Thank you all for the excellent posts. I hope to be able to return the favor sometime. Paul

 

[Steve83]

The strongest way to attach panels is with panel adhesive. It doesn't re-temper the metal. It doesn't create stress risers. It doesn't remove the galvanizing. It doesn't cause warping. It doesn't damage paint or undercoating on the other sides of the panels. It self-primes/paints/seals the seam. Fit the patch panel to the original body contour, drill where you would expect spot welds to be, STEEL pop-rivet the repair panel with adhesive into place, then seam-seal the rivets (remove the nails for the best results). It's the method Ford recommends for field repairs to '78-96 Bronco bodies where they crack above the doors, and for the access hole to make that repair. Here's that TSB & photos of it being done:

 

[cool66bronco]

Great, Great information here on floor panel pairs. My additional question is what if you do not want to see the seam on floor which I think would be visible with seam sealer. What can you use to make the seam go away and have a nicely painted exposed floor? One that would stand up over time?
Thanks Jerry

 

[Steve83]

Carpet, floor mats, bedliner...

 

[Mark]

here's how I do it...
http://classicbroncos.com/forums/showthread.php?t=142374