Fill Coats

The first coat of epoxy glues the fiberglass to the hull, but additional coats are needed to fully wet out the fiberglass, and to get a thick enough layer of epoxy so that you can sand it down without sanding through the fiberglass and compromising the strength.

When adding fill coats, you can simply roll on new epoxy over the old, as long as the old epoxy hasn't cured fully. Once fully cured, it puts off a oily residue (amine blush) and gets so hard that new epoxy doesn't adhere well. So, the plan is to do 2 fill coats, sand out rough spots, and do one more fill coat, 3 days in a row.

Good plan, unfortunately life got in the way. Got through first 2 fill coats in 2 days, then had to wait 2 1/2 days. In our heat, the epoxy is pretty much cured after that long. So, after reading some stuff online, I decided to wet sand the hull to knock off the amine blush and get the rough spots. I did not do a great job with this. I didn't sand quite enough. Also, I worried that I needed to let the boat fully dry overnight in case the epoxy absorbed a little water, but then worried that would just result in more amine blush. I went ahead and did the last fill coat after a few hours, but worried about it. The epoxy did seem to streak a little, but might be my imagination. In the end, it seems it will all be OK because I'll have to sand one more time before putting on varnish. Wait a pain though, I thought the fill coat steps would be easy, but ended up causing a lot of grief.