After being in the house for about 7 years, we decided to repaint. We hired a professional painter. Everything came out fine. A few months later, the paint in the smallest bathroom started to blister. We had used the best paint available for bathrooms. Prior to repainting, there was no blistering, though the tape on some seams had started to peel a bit. The painter came back out, scraped off everything that was loose, reprimed and repainted. A few months later- same problem. He came out again. This time, we replaced the exahust fan with a stronger fan and vented it to the eave. He scraped, primed, painted. This time we let the primer dry for a month (and no blistering). He then painted, and we let it dry for a week before using the shower in that bathroom. A few months later- same problem. In each case, the blistering occurred in the spring or fall, when the heat pump/ac was least active, so the air was not drying very quickly.
Anyway... What is the least expensive way to fix this problem? Wallpaper is fine, if that will work. Our painter doesn't think it will, but I am not so sure of his knowledge now. I don't know if the previous owners had used an oil-based (or other non-latex) paint prior. Oh, one other intersting thing- when he scraped the last time, in some areas the paint came off all the way down to the greeenboard. No mold or mildew, just blistering like crazy.