Blush can be a problem...I had a kayak (one of my first) delaminate between the precoated wood and the fiberglass after a few years use. The fiberglass could be peeled off in large sheets. I didnt know about blush in '91. I was using a 4-1 mix epoxy in a space heated with a kerosene heater...the humidity and fumes form the heater made the bush worse. I do not recall if i knew enough to wash down the boat prior to a second coat of epoxy...probably not. I probably didn't do much sanding either.

P.S. after peeling and sanding the kayak I refinished it with excellent results. the boat was better than ever.