Hello; few weeks ago I laminated something with a non surfboard resin then applied a filler coat (epoxy too) and let it dry for couple of weeks however when I started to sand it down I noticed that all the filler wanted to peel off and in fact did it.
Epoxy resin is only a great glue and a crap for most anything if you do not have the right conditions of weather and possibly that could be the culprit? You know, cold plus humidity.
I warmed the resin and the proportions (5:3) were right.
I am not talking about a finish coat where you can sand the previous coat to 80 to have anchorage but you do not sand a stratificated surface to apply a filler coat...