I could count on helpful replies!
The stuff remains wonderfully messy even with heater going, so I will take it out.
Mike: The weather happened not to be overly humid, so I'm hoping that will not be an ongoing concern as I finish this. (Caution: check my location, but please do not laugh).
Con: I believe you have solved the mystery. The can was old, and the little catalyst left was equally old (it looked like most of it had somehow evaporated). I got new stuff a short time ago and will start from the other side as a test. Good thing it was just a small test area. I used a respirator with the appropriate filters for this, and I could not smell the odor through it. Fans going at the same time, natch.
Loren: In effect I try to have somewhat of a tunnel effect in that large
but enclosed bathroom space. My computer fan (brush-less) methane extractor in the ceiling is remarkably effective, and I learned from my friendly local hardware man this morning that the fumes are lighter than air, meaning that pooling at the floor level is unlikely, so my "radiator" on the floor should not pose a problem.
(Aside to Loren): I have a much simpler task finishing harpsichord soundboards: a couple of wipe-on coats of quite thin wax-free freshly dissolved shellac is all it takes to protect the spruce. Much easier to paint
all those flowers, bugs, and bees on that kind of surface too. For the ultimate in true 18th C. effect it needs a gentle layer of dust, of course.