Correct me if I'm wrong.....shouldn't you epoxy coat the bare metal before any filler is applied? To me it seals off the bare metal and the filler would stick to the epoxy just as well. I'm by no means an expert but haven't heard this suggested yet.
Well this is not entirely accurate. Filler is a combination of resin, talc and microbeads(which are glass). At least lightweight fillers are which is the most common type in North America. The mircobead help make it easier to sand. Talc or Talcum is like baby powder. Ever see what that does with water? Wicks it up like a towel. That is what absorbs and holds the water in filler. Your right the resin doesn't hold water but the talc is like a sponge.
+1 - I have had great luck using the Mar-Glass for the first coat and if you need more filler you can use regulal bondo after rough that out.
Hey i did a 71 bug and on all the pannels that i welded i was told to use f/g and then use body filler i thought this was just a way to sell me more stuff. The body work on that car lasted 7 years and did not crack i guess i wanted to know if just body filler would work