weld through primer

I've used 3M weldthru but didn't work very well for me. I now use U-POL if I can find it, or SEM.
I also figured out that my welder doesn't like to weld fresh sandblasted metal.

I like to run over the the areas I intend to weld with a 50 or 80 grit grinder to shine it up first then a light coat of primer.
Maybe its all in my head, but it seems to work.