> Here is the cause of my concern: This is my first boat, and I was not very
> neat while filleting inside. After I taped and glassed the inside, I
> noticed the effect of the wood flour on the color of the seams. As the
> seams fair out, the thickener leaves areas darker. Obviously, I want to
> avoid these effects on the outside of the hull.

I used wood flour/cabosil thickener for my fillets in my Chesapeake. Where I faired out these seams, the thickened epoxy filleting mixture spread out and disappeared at the edges. Now that everything is finished, the middles of the fillets are very dark and opaque, fading gradually out to clear fiberglass over the wood--the result is not unattractive, and it's inside the boat anyway. At any rate, you've got some darker spots due to epoxy outside the boat; putting on new epoxy with the glass will match the previous epoxy. Don't worry too much about a bit of thickener--it is so thin, it won't develop enough opaqueness so as to be noticeable.

> My gut feeling is that if epoxy plus wood flour cures on a surface, the
> epoxy soaks IN and the thickener stays ABOVE the surface. So, if I scrape
> off the wood flour, the remaining darkening is just due to epoxy resin,
> and will disappear as soon as more epoxy is applied during glassing.

Go with your gut instincts, man!

Happy building, Shawn