I have come across some mold in an enclosed area between a tub and an outside wall. Since I have not been able to find any other source for the moisture, is it possible that each time we run a hot bath that condensation is forming in that space due to the cold air on the outside wall? If so, can that be taken care of with proper ventilation - there is a ventilation fan in the bathroom, but the space in question is enclosed, so I'm not sure what to do to properly ventilate it. Also, the outside wall is sheetrock - should another material have been used there, should it be replaced?

 

I think you should give some more info on what the exterior wall is made of. Like what kind of siding is on the outside[I hope it is not Sheetrock exposed to the elements ] I assume you mean the inside of the outside wall is sheetrock, 2by4 construction, interior wall[what's on it tile, plastic, paint, any vapor barrier.

Is the mold directly between the tub and the ouside wall[meaning not behind whatever is on the wall above the tub? but the actual tub itself 15" off the floor? Is it possible that the joint where the top of the tub meets the all is leaking? Is there a shower?

It is not uncommon to find mouldy sheetrock that has gotten damp or wet in the tub area. It is not an acceptable material for this purpose. It needs to be replaced if it is on the inside around the tub.

Greenboard is also not a great material. I think You could use either regular sheet rock or greenboard or none if you put up a plastic tub surround with the apprpriate vapor barrier on the inside.

You may get better help in the ceramic tile forum imo. yours is not a tile problem but they know what to do there to eliminate the mold.

 

Thanks.

Yes, I meant the inside of the outside wall is sheetrock - it appears to be no different than any of the other interior walls. The outside of the outside wall is brick. The mold was on the sheet rock in the enclosed area. Since I can not definitively determine the source of the moisture, I think I need to have a plumber disassemble the marble enclosure and check for leaks in the pipes, valves, overflow drain, etc. (not something I have added to my repertoire) I have cleaned the sheetrock the best I can, which is difficult since I cannot get inside the enclosure without disassembling the marble. The sheetrock does not appear to be damaged - it isn't soft or crumbling, but I'm concerned what might be going on behind it.