I used a primer sealer above the shower before applying a flat latex top
coat, I replaced the exhaust fan from 50 cfm to 130 cfm plenty of suction.
I have noticed that there are some spots on the wall above the shower, where
the paint is blistering, and other areas where the top coat is blotchy,as if
whats underneath the top coat is trying to bleed thru.The top coat is a
violet color, the color before that was a white.
What can I use to seal the existing paint above the shower before I re-coat
I have seen that in a high humidity area where hot humid air from
outside leaked into the bathroom through the bath exhaust fan. It then
caused condensation on the ceiling around the exhaust fan. The ceiling
was cold from the air conditioner, which helped cause the condensation.
The house had too large attic exhaust fans that pulled air out of the
attic, which in turn pulled air out of the house and which in turn
backdrafted the bath exhaust fan. It was even worse when the wind was
blowing. You can not fix all problems with a bigger fan. The answer
may be a better paint, or it may be a smaller fan or fans. Where your
house is located has a lot to do with the answer.
Flat is the most porus then semi then gloss then oil. Blochyness could
be mold working through. Soap residue could be there to. Clean and redo
with a better higher gloss paint. Sometimes bath problems can be hard to
figure out and will fail till you get it right.
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.
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.
If you're going to tile then yeah, use cement board. The damage in the
original post was above the tile or whatever they used for the shower.
I've never had a problem with the procedure I suggested. The drywall
will be sealed and, as long as the fan is vented properly, there won't
be any problems like that cause by using flat paint.
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