Tumbled marble shower with mold / mildew

Q. Black spots are starting to form on the grout--is this mold?--or some other form of a deposit? The shower is in the master bath and well ventilated. How should I clean the grout on the floor and wall where it is beginning to turn orange?

 

A. Black spots do sound like mold or mildew. I would first try taking a cloth and soaking it with MB Stone Care MB-9 Mildew Stain Remover and let it sit over one of the spots for a few hours. If the black disappears then it is mold, algae or mildew. This type of biological growth is the result of moisture. You may want to dry the shower out for a few days by placing some fans in the shower and then apply a good stone impregnator which should help.

 

For routine cleaning, spritz on a little MB Stone Care MB-5 (http://www.mbstonecare.com) after everyone has showered for the day and wipe with a squeegee.