Epoxy resin isnt "harder than concrete", though it doesnt sand especially quickly. Neither does poly, though. An angle grinder with a suitable attachment (like a flap disc) will make quick work of major high spots. A random orbital or palm sander can do the rest.
If you use the epoxy for the repair (as I would) then be sure to use a conversion coat (like vinylester) prior to laying gel, as it wont adhere as well directly to the epoxy. Im not sure you would want to do the repair in poly though... unless MC builds their hulls with it. I thought they used vinyl, but ICBW.
Last edited by TRBenj; 01-11-2013 at 05:41 PM.