The silica is added to lighten the mix color. Sanding dust seems to get pretty much darker then the surrounding wood. Bleached flour works just fine, too. I made a zero seam yak in the third and fourth yaks using this approack to patch the inevitable gaps. Color, not consistency is the key objective in order to make a yak without the obvious lines. Decks or hulls with a light-colored wood is the supreme challenge; a perfect match is the ultimate acheivement. Give it a whirl,works pretty good, but it takes patience to match color.

: I would mix up a small amount of epoxy with some sanding dust (no silica)
: This should be a moderatly stiff peanut butter consistancy, 'cause the dry
: wood will wick out some of the epoxy; stiffining up the mixture.
: force it into the cracks as you would with putty. let it set to the green
: stage, then scrape (don't sand) it faired. then finish with your
: satureation coat and continue as normal