I've recently sanded down an enlongated center portion of the hull of a kayak.  Down to the original fiberglass covering.  I then re-glassed it for strength and durability.  Then applied two thin coats of epoxy/graphite.  On top of that after sanding smooth, one coat of unthickened epoxy.  All the coats were done with West Systems fast hardner.  I did not detect any amine blush throughout the process until after applying a coat of urethane.  Now where the epoxying was done it is a unsandable, soft, dull finish.   What is the best way to get rid of the polyurethane coat so as to scotch pad and warm soapy water the blush away?  I'm thinking scraper but that may be overkill?  Please for sugestions.  I'm sure I'm not the first to ignore the warnings of West Systems Fast hardner.