im restoring a classic car that does not offer replacement rear quarter panels so i had to hand fab. them up out out of sheet metal, naturally there will have to be some body filler, iv been using "RAGE" body filler, its good stuff, but i found that even on completely ground and prepped bare metal the filler will chip off like it wasnt prepped.. is it because i didnt put any type of meatal sealer, or primer over the metal? any ideas? it doesnt do it every where just very small areas. iv ruled out the possibility of oil contamination and unprepped surfaces
thanks
joe

 

if you spread filler on a area that hasn't been sanded, it will have a bigger chance of chipping or cracking. some fillers do ok over 80grit but for best results, give it teeth by using 40 or 80 grit on bare metal and feather the paint back. i do it that way to keep the surprises away.

 

if you want pic's , there is some on my sig. (hatch project)

 

^ Good advice.

The most important thing is the way in which you prep it. Just because it's roughed up or ground down to bare metal, that doesn't mean it was done with the proper grit. How are you prepping the surface before filler?

 

the surface is ground down completely with a 36 grit flapper wheel.. im also thinking that maybe it is because when the filler starts to harden, it gets thicker, thus making it harder to squeeze into those scratches