From the horses mouth (Larry at Raka):

"Mix resin and hardener first, then add filler. Theoretically, when you add fillers, they add space in the epoxy and keep it cooler, thus extending the final cure time, but usually filled epoxy ends up being in a bigger mass like a fillet and mass makes more heat during cure thus actually speeding up the cure time."

: Unless you're working at very reduced temperatures (temperature effects the
: cure times of resin) or you're not getting the resin/hardener mixed
: properly before the filler is added, the filler shouldn't effect the
: resin's cure time at all. I've not used Raka but perhaps you are getting a
: reaction between the resin/hardener and the filler?

: Sometimes it's a little hard to troubleshoot epoxy problems remotely.

: Bill H.