Our bathroom has popcorn ceilings and we bought some of the styrofoam ceiling tiles to put up. However we have had problems with mold on the ceiling because the bathroom is tiny, without a window. The room does have a small ceiling mounted vent, that we run when we shower. I have scraped off the popcorn ceiling above the shower where the mold was the worst and then painted a coat of Kilz primer over the entire bathroom ceiling. So my question is this, what will I need to do to ensure that moisture is getting underneath the tiles and creating mold where I can't see it?
The important word here is Preparation, preparation. If you have scraped the
popcorn off and sanded the areas good then the mold should not come back.
Also moisture can settle in for many reasons and consider checking
a leak behind the wall, maybe the bent is not pushing air to the outside
as sometimes they are mounted but not ran correctly to the outside.
So to answer your question the tiles will not hold or obtain mold or mildew,but
if you prep the area correctly by either solving the leak, removing the old
drywall and adding new or checking the exhaust fan then you should be good to go.