Tiger Seal...

[driftwood]

I'm fitting a new rear inner wheel arch to my BMW E30 325i 2 door saloon, or will be soon. The join where the inner and outer wheel arches meet was originally spot welded. I don't have a spot welder so my options are plug welding or tacking with a mig welder. I don't want rust coming back between the panels so would like to paint the mating surfaces. The problem is that paint will burn away or prevent a good weld. I've tried weld through primer in the past and it's crap.
I did a bit of research and found that body shops tend to use a bonding agent in this area. I can't justify buying the 3m 2 part epoxy and applicator. Would tiger seal be an option? If so what surface preparation should be done? Bare metal or a primer/paint? Any advice would be appreciated.

 

[bump]

Plug weld it and then run tiger seal in the gap between the panels. Should solve the issue.

As for surface prep, it'll stick to anything so nothing special needed.

 

[andeep]

Weld thru primer on the mating services, then scrape out the holes where you are going to plug weld. After this epoxy primer the area and then tigerseal on top of it.

 

[driftwood]

I bought the u-pol zinc weld through primer. It's supposed to be quite good but after it causing me to have to redo my work several times, I'll never use it again. I scratched off the paint where I wanted to plug weld - made no difference. I've tried thin coats and thick coats. I've tried different welder settings and different gasses. It doesn't matter, the same fault occurs - the welder spits back and the paint around where I need to weld blackens and weld gets contaminated. It looks a right mess and there's no penetration. Also the primer burns away around the weld so I end up with rust again. I thought that on this occasion I'd just stick the wheel arch lips together. There shouldn't be any problems with distortion...
So, etch primer followed by epoxy primer then glue, or just one type of primer, or no primer/paint. It's not a concours car and it won't be getting done again during my ownership

 

[bump]

I've never been a fan of weld through primer. Epoxy before and removing where you weld kind of works, but the heat will cause it to burn off. I've just stuck to working with bare metal at the joints and sealing out the water, with epoxy as the base primer of course If in doubt check out Langy's work.

 

[ajlelectronics]

No point in etch primer before epoxy.