Bad things - after three days, the grey primer still is clogging the sandpaper, wet or dry. It just didn't dry correctly, feels a little rubbery. Now this is the same can I have used before on other (plastic) projects, and it dried fine overnight. I suspect some chemical thing with the epoxy primer.

Nothing to do but get the thinner and wipe the entire plane clean. It took me half a roll of paper towels, 2 cups of thinner and about an hour and a half. What a messy, stinky job. *sigh*

Shot another coat of epoxy primer last night, and it looks good.