I can't comment on the addition of carborundum, but I have used graphite.

Silicon carbide and graphite are to be used as additives to epoxy matrix glass fibre composites for improving certain properties. What type and what processing is required on Silicon carbide and graphite to ensure wettability with epoxy resin. There is also an issue of density difference between epoxy resin and   Silicon carbide/graphite which may cause problem in mixing. Thanks all.