Fungal growth in indoor environments is always related to factors involving moisture. Many fungal problems occur in averagely dry places where dampness is only produced over short periods of time, like bathrooms. Porous finishing materials such as gypsum plaster may retain moisture over long periods of time, resulting in increased risks of fungal growth. In the case of transient moisture loads, fungal growth risks are therefore related to material properties. Specially formulated organic coatings, preferably waterborne, may regulate moisture transport in gypsum based materials and consequently decrease risks of fungal growth. Experimental determination and description of moisture transport in the combined system of coating and base material are necessary for subsequent development of such coating systems.