My goodness! Whatta canna worms!
However, the discussion has been very useful. From the links you
provided and the information in the posts, I have deduced a few
1) Shellac may be a good water vapor barrier, but not a good liquid
water barrier when in contact with liquid water, such as condensed
2) Shellac is not flexible, hence is vulnerable to repeated expansion/
contraction cycles, and this is just what one would expect in the
bathroom doors, with repeated humid/dry, cold/warm cycles. Maybe my
finish was developing microcracks and allowing water beneath the
3) nailshooter41 guessed right, although I didn't "use Zinsser (or
products off the shelf", I am "not a full time finisher,
because" I DID "mix dewaxed shellac just to
use in a bathroom". Dewaxed orange shellac, purchased from Mr. Paddy
Olguin, 2-lb cut in denatured alcohol, three coats. Took fer-f****n-
ever, but it sure looks nice (except for the doors, of course).
4) Recoating with shellac, although probably pretty easy, is probably
not the best thing to do.
SO, I will recoat the affected areas (2 big doors, 2 medicine chest
doors, and various trim) with some kind of varnish, but not spar
varnish. I would prefer to use a less toxic varnish, and I know that
the technology has improved markedly in the past few years, as we have
a water-based floor finish that has held up extremely well on our red
oak floors. Any suggestions on finishes?