Pop Rivets
 

I've read about these and they seem like a good idea for places that I'd rather not weld. I don't have the tool, but they seem to be reasonably inexpensive. Does anyone have experience with these? Why would I rivet something instead of just using something like a self-tapping screw? Since I already have a welder, should I not bother?

I'm not a fan of pop rivets on cars. They do not seal the moisture out like welds or good fiberglass repairs. Usually the car will start rusting around the riveted area, and you'll have holes again.

A mechanic I know recommended using PL-400 adhesive along with rivets on repairs that needn't be pretty. The PL-400 will seal the moisture out.

I might be wrong but I believe riveted repairs are illegal in the UK - check to make sure that any repair you make with rivets are not going to cause you any trouble at your next inspection.

Tucker pop rivets are not strong. There are similar dowel type rivets (with many different names) used through out the aircraft industry. These are much stronger than the widely available pop rivets. However, in the aircraft industry old school thought is that you should always use a solid rivet when ever you can. Only use the dowel type rivets when you can not get to both sides of the joint you are making - a blind riveted joint.

The main benefit of a riveted joint is that you can drill out the rivet to make future repairs. However I'd advise regular checking of any riveted joint (much like in an aircraft maintenance schedule) to make sure there are no signs of movement. Obvious signs are signs of ripping and tearing - but you also get black residue (much like when you polish metal) from movement as well.

I'm only interested in blind riveting, if I can get to the back, I'd rather weld.

Is the use of adhesive only for sealing, or is it meant to add structure? I'm not sure if I trust glue, I'm having enough trouble trusting rivets.

So what about using self-tapping screws instead? I'm not sure if anyone's done this, but would there be any reason not to use them?

same rust reason as the pop rivets. Probably worse in my opinion, as the screw would almost invite corrosion. Might be really short term. At least with riveting, you can treat and paint the hole beforehand, rather than just cutting the hole as you screw.

If you can get to the back with a piece of steel, you can maybe use buck rivets which are solid and really only need something hard to crush against on the back side. All those mid size delivery trucks are almost completely constructed of buck rivets, and they are very strong. Like a UPS truck.

But if you can get to the back, you might as well weld since you have the welder as you say. What part are you talking about? I think you and I are doing almost the same repairs!

I'm most concerned with the inner rocker panel, which I think might be part of the floor pan, it's the panel that the seat belt bolts into. I also watched this video where this guy used rivets because he was afraid of warping the thin metal. You make a good point about the corrosion, I was just curious why everyone uses rivets instead of screws, there's almost definitely a good reason.

Ive got the same rust there as well. I went ahead and completely cut enough of that inner panel out that I can weld the outer rocker panel from the inside, then I will weld the inner back in and weld it to the new patch.

The stuff is thin, but I think the door panel which you have been using is almost the same thickness! Plus, if it warps a little, so what? won't hurt if the seat belt bolt is not square, just so its attached firmly

The reason is that rivets don't - well shouldn't - come loose. Where as screws are designed to come loose - albeit ideally when you want them too!

Dont use pop rivets on anything that is structural. They dont have the required strength. They do come loose under load & are a PITA.
I am concerned that mention is made of metal including a seat belt mount, that is way too important for your safety for pop rivets. You dont want the metal around the mount failing & your head going through the wind shield!
Mig or tig weld is fine. If the metal is too thin, then chances are it has corroded away too much.

Pop rivet tools were made first in the early 1960s, when MIG welding was rare and most welding was done by gas, and panels were thick. There were no adhesives like PL-400 in those days.

It's a matter of history and what was available. In those days people used flat panels coated both sides with polyseamseal, which was the first silicone, then pop riveted, esp in areas where it was difficult to reach or where appearance didn't matter, like the trunk space.

The poly was salt resistant and in an area like Detroit, that was needed. After a year, the poly wore off, you scraped it and replaced it with undercoat.

Obviously this was long before galvanized steel was used. The pop rivet tool was HYDRAULIC because the rivets were steel, not aluminum.

I wasn't sure on the warping, but I thought I'd mention it. I'm more interested in the rivets for places that are hard (if not impossible) to get to the back of.

What about welding in support for the seat belt and pop riveting the rest? I could do that.

you are talking about places where the welding would be over a closed channel and you won't be able to get to the back and paint? Like the rocker channel once you close it up?

As long as its structually repaired, I see no reason why pop rives would not be great to close up a sheet metal opening that is not providing any strength of any kind. Heck, you could even weld a piece of angle iron along the bottom of the floor for strength, and put in a removable panel in the rocker with rivets so you can paint everywhere else, then close it up, or inspect down the road.
A pop rivet should be perfectly fine for something like that, just don't depend on the rivets for structure or for weight. There are tons of fasteners on a car that are way weaker than a pop rivet that are just holding sound, or cover panels.

There is weld through primer to cover the back of the weld as well, and other treatments for this type of scenario.

Here is a thread about my driver side rust situation, kinda similar to the rot you are dealing with, except you have that floor pan under the pedals issue as well. http://www.superturbodiesel.com/std/emergency-rust-repairs-t-1276.html

It's painting as well as cleaning. Like the front seat supports, the spot welds on the DS tunnel would be nearly impossible to get to to clean and paint. I can get to bare metal with sandpaper and my hand when it's just paint, but theres undercoating down there too and I can't get my angle grinder down there.

A heat gun should make that unbelievable undercoating more pliable, and able to tear it back. Honestly, I got so tired of dealing with the undercoating, that in several areas where I had immediate access to the back side I just welded the one side and put the undercoating fire out with a sopping towel every 30 seconds or so. Not all that safe, but it sure saved a lot of time.

If you want all the room in the world though, you should pull the drive shaft. (depending on the condition of the bolts)