I have zero credibility in this thread since I thought mat and epoxy was fine, but I think I understand what stu means. When I used them together, I did fill the void with something hard. I did get the mat wet with epoxy; there weren't bubbles or soft spots. But according to the info I read the other day, the mat was supposed to unbind and have the fibers mix so that they would bond like one unit and I guess that didn't happen.
But stu, think about this (and try it if you're really bored) - if you soak an old sock in thickened epoxy and let it dry I bet you can whack it pretty hard with that screwdriver and it will feel pretty solid. But even the crazy cheapskate doesn't build or repair boats with old socks...
Newport 17 - "Kohanna"
At sea Darwin's hypotheses is the final arbiter of right of way.