Welding new floors on top of old

[AdamG8GXP]

So I got around to fixing the floors and found someone who would weld them in as a side job for pretty cheap. Now his welder sucks and it very easy to burn right thru new 18 gauge floors and there are gaps. We are putting in the new pans on top of old ones (again, cheap) and they are primed on the bottom.

I was thinking of sealing the gaps and all the way around the pans with black RTV or caulk.

What is good to use for sealing inside a vehicle to stand heat, cold, have no fumes and smell when dried (I know asphalt will melt and smell in the summer)?

Here are pic of the floor in my 1994 Cherokee Sport 4.0L, manual, 4x4

 

[Corprin]

You are going to need to cut all that rust out... all of it. If any is left you will just spread it to your new pans. I just went through this process, and the prep took much longer than the welding/sealing. I used body sealant to do the edges, and over-coated with spray on bed liner (6 coats).

If your welder is prone to burning through 18ga, he needs to learn to weld better, or find a new buddy to do the welds. If you were closer to Minneapolis, I would invite you over to do the work here, and the welds in exchange for some beer from a specific brewery on your way I am sure you can find a local 4x4 or muscle guy to do the same for you, just have all the prep done, and needing only the welds to be burned in.

I have a link at home that I will post up with step by step how-to instructions on the swap.

 

[AdamG8GXP]

He said something about welder not having gas. I think he didn't weld stuff this thin before.

I think if Jeep floors lasted 17 years, these will be ok for a while. Also it has 256k miles and it might die soon. Jeep is gonna be my winter car, and I wanna try some wheeling but I only found Badlands offroad park in Indiana which is 5 hour drive one way so not really getting into wheeling if its that far.
For now I just want to keep stuff out of Jeep, road noise, water...

 

[Matthew Currie]

In my experience RTV and its relatives don't stay that well with rusty metal, and seem to separate and draw in more rust. My old standby is roofing tar. Unless you get unusual amounts of heat, it sets pretty nicely and stays pliable. It also tends to self-heal a little, filling gaps. After all, it's meant not to melt off a hot tin roof. I never noticed problems with the smell when I put the carpets back in. If it does smell, it's nicer than soggy mildewed carpet.

If I were doing this, I would cut out the worst of the old rusty spots to make clean holes where possible. You can't do that on spots that fall over the frame, etc., of course, but open holes should be cleaned up. The less active rust you are left with the better. Prime as much as you can, and use the tar liberally as a gasket around them when you lay down the new pieces. How much you can put on before welding will depend on how hot things get while welding, so you may have to do it after, especially if the welder and weldor together aren't the best.

I've always preferrred screwing in sheet metal to welding, because I think it's easier and just as effective, and much quicker, but I've never done this with an actual floor panel rather than pieces of sheet metal cut to shape. Self-drilling hex head screws make this job a breeze.

Once it's put together, get above and below, and goop the **** out of everything. Try to get as much goop in between the layers as you can, and to seal the edges of the original holes so moisture doesn't work between the layers. Even if you've welded the edges, you might consider using some self-drilling sheet metal screws around the margins of the holes, to draw the layers together. If you goop first, then screw, it will squeeze together pretty well.

 

[AdamG8GXP]

So roofing tar sandwiched between old and new floor pan?

And prime the new pans or old? (I will paint the top of new pans, and primed bottom of new pans already)

 

[gdl90xj]

I went through something similar, on a 1990

I screwed in sheet metal where needed

Removed rusted out areas, and before screwing new sheet metal I painted everything before with rustbullet (marine anti-rust paint) both old and new metal.

The rug was trashed and was replaced by heavy duty rubber floor, heat on the passenger side could get nasty

Sold it 2 years later, that repair was holding perfectly

EDIT: I did seal with RTV

 

[AdamG8GXP]

He can't weld the pan all the way around. It burns thru it. He might spot weld it.
1. With spot welding, is it even worth it? I keep reading about how Cherokee is a unibody and needs its panels to be completely welded for structural integrity, this makes sense to me. If I go with spot welding, I think I might as well go with self with self tapping screws and fire the guy (agreement is $200 but for welding them in completely all the way around). Thoughts?
2. What do I lose by spot welding and using self tapping screws for new pans instead of welding them in completely?

 

[AdamG8GXP]

I went through something similar, on a 1990

I screwed in sheet metal where needed

Removed rusted out areas, and before screwing new sheet metal I painted everything before with rustbullet (marine anti-rust paint) both old and new metal.

The rug was trashed and was replaced by heavy duty rubber floor, heat on the passenger side could get nasty

Sold it 2 years later, that repair was holding perfectly

Thanks for replying.
I see. I can do that. I wanted to hire someone to weld the pans but this guy really can't.

 

[AdamG8GXP]

My guy is scared to death of welding cargo are because of gas tank.

Does welding the cargo area is a fire problem?
Empty or full gas tank?

 

[Sillyfast]

I had to do 70% of my floors. Cut all the rust out. welded all new 14gauge in. When I did the back I removed the gas tank because I didn't want to blow myself up.

 

[AdamG8GXP]

Thanks for pictures. This helps to show it to my guy.

If anything, does anyone know someone to weld it properly around Chicago are to give me quote?

 

[Matthew Currie]

I've been in this boat more than once, and here is my basic take on rust repairs.

If you're trying to restore a vehicle to rust-free condition, weld as well and as much as you can. Spare no expense if you're doing a real restoration. Likewise, if you are patching rust holes in the visible body, nothing works as well as welding, and you'll never be satisfied with resin or pop rivets above the level of the rocker panels.

But if you're trying to keep an old and rusty vehicle on the road and basically safe and decent, don't put too much energy into perfect welding on the invisible parts. You'll spend hours and hours and bucks and bucks doing a beautiful job and a year later there will be rust holes next to the ones you fixed. I've done this, and it's frustrating.

As far as priming and such goes, I don't think it's possible to prime or paint too much. Paint and seal everything you can possibly reach, and when you're done, paint it again. If you're screwing things together, sandwich with tar and it will squeeze into the interstices and help seal out moisture.

I would not weld over the gas tank empty or full. If your Jeep is rusty, can you be 100 percent sure there's no little leak in the tank ready to emit that one little puff of vapor that blows you sky high? I'd drop the tank. Besides, if you haven't looked at the top of the tank, now is a perfect time to do it, and make sure it's not covered with corrosive crud and sand, eating holes. It's the perfect time to clean that up and paint it too.

The last major screw and goo job I did was on my stepson's 93 XJ, which had much bigger holes in the floor than the pictures in this thread. Huge, all over. I used my favorite material, old metal shower stalls, cut to shape and banged to contour as needed, screwed and gooed. It lasted for years.

 

[Corprin]

http://www.naxja.org/forum/showthread.php?t=906957

 

[AdamG8GXP]

Thanks for this.

 

[AdamG8GXP]

@Matthew Currie - What did you use to goop up the gaps?

Alright! So the new floor pans are in. Not very happy with it as there are gaps between welds. (If anyone wants to pick up a side job, let me know).


What should I use to goop up the gaps?

 

[Matthew Currie]

First of all, if there's overlap and significant separation, I'd add a few screws. If it's just a few gaps in overlapped pieces, the goop should suffice, but it works best if the pieces don't flex relative to each other.

My goop of choice has always been brushable roofing tar. You can get it in gallon cans from home supply outfits. It's stiff, and requires a stiffer brush than a regular paintbrush (parts cleaning brushes work pretty well), or you can slather it on with a paint stirrer or other paddle. It's messy as all get-out, but dries reasonably firm without hardening, and migrates pretty well into gaps.

However, it won't bridge a hole, so if you actually have open gaps in seams you'll have to cover them with something. Either another piece of metal, or at least some kind of material that can be stuck down and sealed.

Needless to say, if you are planning to improve the welding job or do further welding, don't apply tar yet.

 

[AdamG8GXP]

I have roofing tar in a tube. And seam sealer.
No, there are no holes but gaps where new tub overlaps old pieces. Will wait a bit as someone took interest and maybe they can fix it up. If not i will inject seam sealer or tar, whichever is better, and tighten it down with hex head self tapping screws

 

[Corprin]

If you make the drive to Minneapolis, I will be happy to fully seam weld that puppy in, and get you taken care of right.... for free.

Here's mine

 

[AdamG8GXP]

Thanks.
Another Cherokee owner helped me. Now I need to clean this up, seal it, and paint it