109jb

Strong enough to bond on a quarter panel? Yes, I'll give you that one. After all, that's what it's made for.

As strong or stronger than a weld? Not a chance.

A proper weld will be as strong as the weakest of the base or filler metal. For a quarter panel that will be about 80,000 psi. 3M's own documentation says a max of 3,935 psi in shear. Adhesives work best in shear and 3,935 is good, but peel strength is always a fraction of the shear strength. Take a piece of scotch tape and stick it to a table with some hanging off the end. Now pull on the free end in the direction of the tape. That's shear strength of the adhesive. Now just peel it off perpendicular to the table top. That's peel strength. This shows the difference between peel strength and shear strength of an adhesive. A quarter panel skin is going to be loaded in shear so the adhesive is fine with enough overlap, but other parts of the car have much different loading. This is why 3M even says in their own literature that Automix is for exterior panels only and not for structural members. Quite simply, it isn't strong enough, but a weld is.

Also, longevity of the adhesive joint is dependent on preparation and absence of voids. If there is a void, especially one where moisture can get in, the bond will eventually fail because it will either rust and the rust growth will try to push the two panels apart, or the moisture will freeze in the cold climates with the same result. Remember peel strength?? A void anywhere will create a stress concentration which may or may not be a problem. An adhesively bonded panel that can take a hit a week after a repair is not necessarily the same after 10 or 20 years. Most cars aren't around that long. A welded joint is the same no matter how long after the repair. Particularly a butt welded joint that can be preped and protected on both sides.

For my Mustang, I chose to weld because I want to know for sure it will last.

jaw66

I would say it is not a good idea. I would never glue a cowl on. You could use it on hard to get to areas when welding but I would do no more than 20% of the panel with it.

rmodel65

they make subcultural adhesives, ever heard of the chevy APV? it stands for all plastic vehicle and is glued together with structural adhesive

rmodel65

different companies use different setups did you use the mixing end on that gun or just mix it together with something?

HGC

At first I put the mixing nozzle on, but honestly, I am not a weak guy but I simply could not squeeze my cheap caulk gun hard enough to get it to flow. Since these are just patches I took the the nozzle off, squeezed the bonder out (it comes out equally) and then mixed it well with a throw away stick. I then used the stick to smear it on the parts, making sure I had full coverage and was plenty thick enough. I used a good number of clamps and screws to try to get a good flat fit everywhere. The product says you cannot overclamp because it contains glass beads designed to prevent all of the material from squeezing out from between the parts. As a safety, I am sealing theedges of the overlapwith a cold weld two part epoxy. Interestingly, this product said not to lift the part to reposition, but to slide instead. Probably to prevent voids. I did slide the parts around some to make sure everything got bond on it. The patch in this post has a minimum of 1 onch overlap and in someplaces more. Per the earlier post here, the hammering I did after cure was a shear load. I did not consider the type of load before. It just happened that I had to do some hammering on the lip and that would have been shear to my installation. I did do some test scraps earlier and I tore the metal trying to separate the pieces. The metal was from repro quarter skins. I also tested bonding without cleaning the metal first, just out of curiousity. I could get that apart by placing one end in a vice and hammering on the other end. Bent the hell out of the metal first though before it separated. Probably more than you wanted to know.

rmodel65

yes your not supposed to lift just like when installing a windshield. i would just use a metal based filler over the seam.

HGC

Can you suggest something? I am not familiar with the metal based fillers. Would that be to minimize moisture intrusion?

rmodel65

the alum based filler are the closets thing to leading the surface that you can get. they use fiberglass resin as a hardner instead of the normal filler creme. i normally go for evercoat products and have good results https://www.autobodytoolmart.com/p-12798-15941.aspx

you can get it from local paint stores also