body filler application

Professor Fate said
Just a suggestion, and not many people follow it anymore; but don't just use filler on your C pillar joints. Find someone who still can do lead. The quarter panel joints need too much filler, and when filler gets too thick, it WILL crack. Not today, maybe not tomorrow, but eventually it will. And there goes your nice expensive paint job. Newer cars don't have as big of a joint to fill, and can get away with it. I know people do it all the time, but I wouldn't. JMO.

If you are talking about regular filler, I agree. When I dig all the lead out of a seam, I smooth it out with a product called Metal 2 Metal by Evercoat. It is a metal-based filler that is VERY strong, cures VERY hard, is waterproof and will not crack. You can also use a fiberglass reinforced filler, but I like the Metal 2 Metal stuff.