: Sanding between fill coats will cut into your cloth.

And that brings me to my problem. I have a good deal of experience with furniture making and finishing but not with fiberglass and epoxy. I thought I would scrape between the first and second fill coats. In some areas the weave got slightly scuffed. I thought the epoxy would penetrate those fiber ends and make them disappear and so was suprised when it didn't happen. So why didn't it happen? It's not noticable from a couple of feet away, but get closer and under the right light and I can see white flecks. It's pretty disappointing considering the effort I'm putting into this. The lesson seems to be to put on two fill coats before sanding. Still it's going to make me wary about sanding too aggressively during final finishing. Hopefully, I can avoid the problem when doing the deck.