OT - Auto Body Repair

In my non-professional experience doing "rust work", epoxy is no substitute for welding -- not even close. Adhesives work OK for new construction if the joints are engineered accordingly. Insurance companies don't care about durability beyond short warranty period. No epoxy yet has anywhere near the strength per unit area of a weld.

Aluminum (aircraft tend to be made of aluminum) is more amenable because welds in aluminum are not as strong as parent metal. Most repair work is done with TIG or MIG which tends to be brittle in thin metal (think cast aluminum), and there aren't many weldors that can gas-weld aluminum well (or at all) anymore. Good aluminum boat repairs (small boats) are therefore done with epoxied patches inside the hull with an external weld mostly for appearance and smooth surface.

About anyone can MIG-weld steel body panels. Muffler shops use MIG rather than clamps anymore, and the young men doing the work are certainly not weldors!

The only epoxy-type adhesive that I used, while working in the autobody repair/refinishing trade, was a 2-part adhesive for Corvette panels (which is the method that they're assembled with). This particular adhesive didn't cure to a fully-hard, but instead, just short of being completely hard (just a bit of flexibility).

I haven't been in the trade for a couple of decades, and many auto manufacturing methods have changed since then. At the time, I think that besides the Vette, the only other production car in the U.S. was the Fiero(?), that had composite body panels.

I'm aware that afterwards, the car manufacturers were beginning to utilize many different alloys of steel, for engineered crush zones in cars. To get certifications in autobody repair, technicians needed training related to proper methods of welding on various structural elements of car bodies. A couple of decades ago, many body shops didn't have MIG or TIG welders, and much of the metalwork was performed by brazing.

Way back when, car bodies were made of mild steel, but not so, anymore. Metal structural body components may be heat-treated alloys that will be weakened by improper welding techniques.

There are a lot of adhesives that work great for specific jobs, when mixed and applied in ways exactly as the manufacturer intended them to be. Slight variations can mean complete failure.

I believe the concept of using adhesives to mount auto body panels sounds foolish, particularly because of different rates of expansion of the different materials. The possibility of failure would seem to be very likely, considering proper surface preparation, shop conditions such as temperature and humidity, widely different interpretations of the proper methods of completing the bonding procedures, and more.

WB metalwork> I have just heard that our local provincial (equivalent of US state)

It works very well as long as the person doing the bonding follows the proper steps in prep work. The two part epoxy is made specifically for bonding the panels. I have used it myself and it holds up very well. When properly used it can be as strong as the panel itself. I did a couple tests when I was first introduced to it. Cleaned a 2 foot square piece of steel and cut it down the center. Bonded the seam with 1" of lap and waited the full cure time. Then I connected it up in the frame table with 6 panel clamps and tried pulling it apart. The steel itself tore apart and the seam held. Did a similar test a couple months ago with the same result.

The key, just like in the rest of body work is PREPARATION.