Should I weld every seam or just lots of solid tacks with some kind of sealer?

I have no idea what I'm doing.

1" weld, then a 1" gap, then a 1" weld, then seam sealer. I recently finished a tunnel in my project. Some of the seams I welded the entire length and then ground smooth. Once its painted it will look like a bent panel. I made mine so its removable. There are 20 or so captive nuts welded into the non removable parts at the front and rear, and 20 or so small bolts holding the center section with the shifter in place. No carpet going back in mine to hide the ugly so I had to really take my time.

Depends on your fabrication. With decent overlap and tight panel fit spot/rosette welds every 4-6 inches will be enough to keep it rigid enough for sealer to stay where you put it. If you're less than 1/2" overlap or not using spot/rosette welding type joinery the panels can flex enough to substantially reduce the sealers lifespan and I'd do a full length weld.

If you run a cutting wheel through both panels and discard the drops you'll have an instant perfect fit for a butt weld.

If you do decide to overlap, and you're not too far in yet, try to fit it so the tunnel is "under" the floor. That way water can't seep into the seam should your sealer fail.

Either way, I think I'd want a full length weld there to eliminate any chance of corrosion starting between the panels.

We stitch welded the factory seams on the challenge car. Rust repair got fully welded. If it was supposed to be one continuous piece from the factory, we made the repair so.

In reply to maschinenbau:

+1 for admission of knowledge.

Before it's in permanently, would there be any advantage in making the tunnel removable for future maintenance or repair?

Normally, I let the professionals help guide me in a good direction, so I see what they're doing. I like having my stuff 100% welded, but many times it's just overkill. Also. for someone that doesn't know what they are doing, that looks pretty darn good. Just watch the heat from here on out. I usually keep a wet rag handy.

I do both - full seam weld and than sealer on top.

Random thought. Have you checked out 3M seam sealer tape? I may be crazy, but it looks to me like it would be tough to motion-crack that stuff.

I'm trying it out on a small transmission tunnel patch used to fill the gap around the re-positioned shifter in a motor/tranny swapped track car. I just riveted the panel in and put the 3m tape over that. We'll see how it holds up.

In reply to maschinenbau:

Anytime I was working with spot welded assemblies I always did a solid weld along the seam.. Testing confirmed that it was stronger..

However to prevent warpage you will have to do short beads and let them cool off completely before you come back to connect them. I'd weld about an inch and move to a spot not affected by the heat from the previous weld..

Thanks everyone. The panels were all hand-formed with hammers, vise grips, a crappy HF brake, and various edges and round corners I could find in my garage. Also forgot to mention there is a 1x1 frame under the sheetmetal that I have been tacking to. So I think I'll seem weld all the sheet seams, and just do spaced out 1" welds between sheet and frame.

Trackmouse said: +1 for admission of knowledge.

The Rice Rod build thread is basically 16 pages worth of "hmmm let's see if this works"