A couple of additional things to bear in mind when using thixotropic agents:

— different thickening agents create different strength joints (e.g., microballoons are great for thickening and fairing, but create a much weaker joint than cab-o-sil or woodflour).

— staight cab-o-sil makes a wonderfully smooth fillet, but the joint is distinctively "white" unless you throw in some wood flour or sawdust to color it a bit.

— the microballoons I received from CLC created a dark red mixture...OK for the inside, but not something you want on an outside joint on a bright finished boat.

From my limited experience, the cab-o-sil/woodflour mixture (about 2:1) has given me the best strength and color match.

While I don't like the extra sanding, I've found that successive thin coats of epoxy seems to avoid major runs.

Good luck!