Originally Posted by dpach
Then the wife came home one day and said 3 of her coworkers.... When they remodelled, they all found the open cavity above the tub enclosure full of mold. The contractors said the enclosed tubs/surrounds tend to get moisture/humidity behind them and since the top foot or so from the enclosure to the ceiling is enclosed behind drywall, there's no air movement up there and the trapped humidity causes the mold. So all three families redid the tub surround in full tile (including ceiling).
For mold to thrive, it needs moisture and food. To minimize the moisture you want to install a properly sized fan. It is also a good idea to put it on a timer so it will run an additional 10 to 20 minutes after a shower.
Mold's most common food in a bathroom is the drywall paper. There are mold or moisture resistant drywalls, (often called greenboard or blueboard) but they are not mold proof. Cementboard isn't quite as easy to work with as drywall, but it has no paper, and so nothing for the mold to eat. You might consider using it behind the shower.