I use Evercoat  Formula 27 filler from West Marine.  The stuff is basicly the same thing as Bondo but it is white which is much easier to cover with white primer/paint than the pink auto body filler.  I think it comes in pint sized cans. 

Mix up some epoxy/hardener and add phenolic microballoons. Very easy to sand, you only mix up as much as you need, very strong in compression, very lightweight.

A balloon-rich mixture is the lightest and easiest to sand, but is very stiff and may be hard to spread. A lean mixture spreads easily, but is heavier and more work to sand. When you're mixing it up, try for a texture like room temperature canned cake frosting.

Also, mix up less than you think you need. The balloons add volume. I'd suggest 1.5 oz of epoxy mix for the first time. Have the balloons in a separate cup and pour in the epoxy mix a little at a time. That way, if it's too rich, you can add more epoxy until it's right.

CLC sells the balloons here. You can also get them at any place that sells epoxy supplies. This is the mix I use to fair all my painted boats, as well as filling the weave whenever I'm not finishing bright.

Have fun,

Laszlo

Many thanks to Jeepguy2 and Laszlo.

Special thanks to Laszlo, who was there for me when I built my first boat - a Wood Duck 10 hybrid.

That was a while ago. Glad to see you are still around!

RichMPL

Me too! :-) Also glad to have been of some help.

Laszlo

Phenolic is absolutely the way to go. Mix it in to the consistency of bondo. Spreads like peanut butter and sands easily.

And wear a mask when mixing.