thinning bondo with fiberglass resin

Just grab a hunk of it and chuck it at the panel. Sprayers are for wimps.

 

This is an old post, however, what I didn't hear in the comments was experimenting first and decide if you think it is what you wanted or not.

 

What I love about the net is all the bs from all the experts. Did any of you stop to ask 3M? It took exactly 12 minutes for them to come back with the answer. Can Bondo Body Filler be thinned? Yes! Up to 25% with fiberglass resin. Use the cream hardener. Drying time will be slower. Do not use Acetone, MEK, Alcohol or brother in laws pee.

 

It's like I asked 3M , can you use panel bond for filler? They said no. Thats why we make filler. LOL

 

As a young know it all, I thought I could save big money by making my own "Featherfill" by thinning "bondo" with styrene (the proper way to thin polyester resin). It would be half the cost, if it worked. Well , it worked as far as spraying it on the fender, and it hardened, pretty much. But it clogged sandpaper liked crazy. I ended up scraping it all off. I suspect it's like jell-coat in that you must seal it off from air , or have a surfactant in the solution to get the surface to harden. Long story short, real polyester primer is worth the extra cost.