: The West System manuals are a great read on epoxy use. Different
: fillers excel at different tasks. Fibers (cotton or glass) are
: good for gluing because they trap some epoxy to help prevent a
: dry joint from over clamping. Fumed silica (Cabosil) make good
: smooth strong fillets and prevent sagging on vertical surfaces
: but is impossible to sand. Mico balloons (glass spheres) are for
: non-structural fairing because it sands easily and has no shear
: strength. Wood dust (sanding dust) is cheap and is wood colored
: but is not as strong as fumed silica or as easy to use for
: fillets.

: http://www.westsystem.com/ss/filler-selection-guide/

The West system book, hardcover, while it's not cheap, is also a great reference, for any epoxy btw, not just theirs.

http://www.amazon.com/Gougeon-Brothers-Boat-Construction-Materials/dp/1878207504/ref=sr_1_2?

Bill H.