I have used both the glass and phenolic microballoons. They are intended primarily as a fairing filler, but I used the glass ones for my Guillemot endpours. I mixed 6 oz. of balloons (by volume!) with 3 oz. of epoxy and it was still flowable.

I think if you added about 1 part glass balloons to 1 part wood flour and 1 part epoxy, and then use cabosil to "thicken to taste", it would work well.

Cabosil is one of the strongest fillers, by far, but it's also very heavy and hard to sand.

Your best bet is to keep the fillets as small as possible. It's my understanding that they're mainly there to make a smooth (read: stronger) transition for the glass tape from the side panel to the bottom panel.

You're glassing the inside (with at least tape) and the outside, so the strength of the fillet is much less of an issue.

Yes, you can use some lightweight fillers, but keeping the fillet size down will be your most effective weight-saving tool.

Shawn

: I am about to start my first kayak with a kit from CLC. I am concerned about
: keeping the weight down. will I save much using microballoons for my
: fillets and such? Are their any other insider tips to keep weight down
: without sacrificing strength too bad? can I do things like rip down my
: shear clamps a bit or am I asking for trouble? any wit or wisdom will be
: appreciated -thanks