painting the back of patch panels

[Frankenstein57]

Looks like I'm going to be replacing the rusted areas on my 57 soon, I'd like to treat the backside of the panels. My rockers are new as well as the right side lower quarter panel. The drivers side is a very clean complete used 57 quarter, I have clean used panels that go on next to the tailgate, under the tail lights. I think a rust paint would be a mess for welding and grinding, I have never used weld through primer. Is it available in a rattle can? And is it suitable for a permanent coating, or is it a primer that needs to be over coated? Thanks for your input, Mark

[RICH MUISE]

I What I did with the patch panels, .... I treated them with Zinc phosphate and por-15'd the backside, keeping a little bit away from the weld areas. You could then spray the weld thru primer in the areas that didn't get por15. For the rear quarters, you can get to most of the areas from the inside on a car..not sure about the Ranchero. You can use the 3M waxy stuff inside the rockers after welding also. The gun has a long wand that you can reach far inside the rockers from the hole in the front under the door post.

[gasman826]

I have mixed experiences with weld through primer.  Yes, it welds better than other paints.  But, it is still a comtaminant to the weld so it impacts the quality of the weld.  It also burns off and leaves no protection at the weld.  It actually leaves some carbonized paint behind so any attempt to coat over it will fail.  The weld area will be the first area rust will attack.  I treat new metal and welds after completing work...even boxed in rockers.  This weld discussion is another reason to review the advantages of bonding with adhesives.