I use 5 min epoxy with milled 'glass all the time, no problems. The more you use, up to about 1/2 glass, 1/2 epoxy, the shorter the working time gets. I only do small jobs that I know I can get done in a couple of minutes, like cowl blocks. Never had a problem with strength, either; BUT, you got to be ready and work fast, or it will set in a heartbeat and you're only half through.