Bob , if you are truly wanting to fair out the rough spots on the bottom of the hull don't use wood flour and epoxy as a fairing compound. It is still too hard and not smooth enough. Use micro-balloons or some other additive especially for sanding. I saw a kit kayak sitting in the rafters of a boatbuilding school that one of the fellows said had been there for over a year. The builders had tried to use cabosil as a filler for fairing and they went on to other things as the boat was about unsandable.