Thanks Rollin, I always varnish before canvasing, to avoid that kind of issue. I do coat the hull with an "Olympic" brand linseed oil based wood preservative, to which I add a little more linseed oil, I wipe the hull down to get rid of excess after it has had some time to soak in, so there should not be free preservative on the hull, though the it can hide out in the cracks between planks sometimes, but I did not see any bleeding through into the canvas, when I canvased the next day, and I filled immediately after putting the canvas on, so preservative may be the culprit, hard to say at this point. The only other thing unusual, is I built this one in mid winter, (no heat) which I never do, but I had an unexpected 36 days off in January, temps were in mid 40's, with the usual high humidity (rain) around here, and a about 2 weeks of freezing temps later on in February. No hurry on this thing, so will wait it out.