Been there done that, had it fail. Replaced the drywall with cement board
and tiled it. The rest of the room I wall papered the ceiling with a
commercial grade vinyl cloth wall paper. No problems after about 20 years
with this method.

"Hopkins" wrote in message
oups.com...
This is assuming the exhaust fan is vented to the outside, and not just
into the attic...

It's odd that the flat top coat would blister, unless it's over a
primer coat that's has some gloss to it [or it's an oil based primer].

Flat is an absolute no-no in a high humidity room. The loose paint
needs to be scraped off. Since I tend to dislike doing things over and
over and cleaning flat paint can be a waste unless there's obvious
residue (and I don't know enough about your bath), one way is to do the
walls/ceiling with a better primer/sealer. At the least you should seal
the ceiling and any other spots.

The blotchiness could be one of several things... the primer/sealer
didn't work, moisture is coming from the backside of the drywall, you
have hard water, there's soap residue.

I would go with an oil-based primer/sealer, followed by 2 finish coats
of latex that has a gloss (satin, semi-gloss, gloss... it's your
choice). Avoid using the shower the day you paint.