Maybe I am over-thinking this. I am replacing the rocker panels on my 280. I have removed the old one, repaired rust to the inner sill and have the inner sill as well as the inside of the rocker panel/outer sill stripped to bare metal. I know that the best approach for bare metal is a self-etching primer but on the contact points where I am going to weld the panel on by plug welding, it would be best to use a weld through primer. Should I paint both areas with the self-etching primer then remove it from the weld area and apply the weld through primer to that area or could I use just one or the other on all surfaces and weld it up? Hope this ramble makes some sense!!!

thats a good idea. Use the self etching/epoxy/por15 the area around the welds. then use weldthru primer for the weld areas. as long as you get as much of that bare metal protected iwth something.

I am at that exact same place with my sills. I am going the with a thorough wire wheel cleanup, ppg dtx579 metal prep, fresh water rinse, air blast and heat gun dry. Then I masked off weld areas and POR15ed the remaining areas. Pulled the tape and used a weld through primer on those areas. When it is all welded up, I will apply a rust inhibitor through the holes in the inner sill. That, along with its new pampered life, ought to hold the rust at bay for at least 20yrs. I'll be far to old to be worrying about it, thats for sure.

Wurth High Zinc weld through primer.

wear a mask