weld thru primers?

I spray the whole seam and let it dry. If im plug welding I clean the areas where I will be welding and it seems to work good. It does burn a little but does not appear to affect the weld quality.
I was using a zinc based type but the price more than doubled when I went to buy another can. I found some "copper weld" and it was priced around $20 a can. I think SEM makes it. Seems to work just as good.