Any time you thin epoxy with alchohol, mek, acetone or ??? you wind up with a weaker final product. Best bet is to just use slow (30 minute or slower) cure epoxy direct. Then heat the area that you have the epoxy on and it will quickly thin out and magically be absorbed into the weave of the cloth. Do not overheat, i.e. not so hot it bubbles. Now lay a layer of Saran Wrap (what your wife uses in the kitchen) and smooth it out with your fingers. Leave set for 12 hours or so then remove the Saran Wrap. You will find a surface so smooth and slick you will be amazed; no sanding required and the edges will be perfectly flared out so no detectable edge to the fiber glassed area.