Generally low density fillets are for light weight, for example microballoons. And then there's high density fillets for greater strenght, such as silica.

In planing boat the fillet material matters, usually in kayak it does not.

You can use wood flour instead, but the volume is usually not really increased while adding the thickener and the result can easily be difficult to spread and sag. The good sides is it's strong and cheap. Another good side it's it ability to even moisture (epoxy) content through the fillet.

I've used also wheat flour. It's easy to acquire and it increases the volume nicely - saving epoxy. It makes fillets that are more easily spreaded and less sagging that wood flour. The bad side is that it will not even the moisture. If underlaying surface is not properly pre-coated, the fillet might not attach well. Also the fillet seems to be a bit more porous or something - doesn't matter if you lay the FG cloth over it.

Some people use the sanding dust from garage floor. Basically it should be good for fillet but there's a risk of water or oils that might prevent epoxy cure.

I personally use wood flour for places where I think the strenght is needed (like using it as a glue) and wheat flour on other parts. It also depends on some other things, like when I'm going to tape it and will it be visible place and such...

Silica being thixotropic should lead to easy non-sagging fillet.

So there's lot's of options. While the strenght will vary between materials, for usual kayak building it does not really matter (if you just use the epoxy and other stuff correctly).

Toni.

: I have read about talc used as a thickener for epoxy but I see nothing about
: the characteristics of advantages. When and why use it?

: Main reason I am asking is I am running out silica and shipping costs for
: something so cheap are a killer. Just wondering how it would work since I
: can pick it up local (I assume anyway). Any other fillers for general use
: I might pick up local?