Moisture on Outside of Bathtub
We have an odor in our linen closet that smells like moisture, musty, etc.
Four months ago we replaced our tub with a new Kohler Villager cast iron bathtub. The installation is in a three-sided alcove with tile surround walls above the tub. Tub, tile and plumbing are new, but in same configuration as before. On the other side of the wall where the plumbing and drain are is a linen closet, with an access panel you can open and see the underside of the tub, the drain, and the valve. The closet has started smelling really musty in the last few weeks. There are no visible drips, moisture on the floor, leaks from drain or supply pipes. The only evident moisture is that when you touch the outside of the tub, (the cast iron part behind the access panel - not the finished part in the bathroom) it feels moist like there is condensate on it. It's all over the tub, not just near the drain and overflow. The house is a 45 year old one-story, central heat/air, unfinished attic. Is it normal to have condensate or moisture on the outside of the tub like that? Is it a problem? Any ideas what could be causing the musty smell in the linen closet? Bathroom is used by two teenagers who take really long showers, but there is an exhaust fan to remove moisture. Weather has gotten cooler in last few weeks, so we are not running AC as much as before, and don't need heat yet, so inside humidity is higher in general.
DensShield Installation Question
When we compare the pictures taken during construction to now, the back (non-tiled) side of the DensShield looks different. It was all a somewhat mottled light brown. Now there is a dark brown band that extends from the bottom edge where it meets the tub up about 6 inches. We can only see one end, but the band goes all the way across the end. My guess is that the DensShield is absorbing water and wicking it up. It looks like they put a bead of clear sealant on the tub, then pushed the edge of the DensShield into it. The instructions say there was supposed to be at least 1/8 inch gap between the bottom of the DensShield and the tub flange, but the gap appears non-existant. The contractor put a flexible, grout colored sealant between the bottom edge of the tile and the tub, but it also is not 1/8 inch wide. Does this sound like a problem and could the DensShield be absorbing water? Could the wet DensShield be the source of moisture in the area, which is then condensing on the tub surface?
Update - Question Contractor's Plan
Thanks for the experienced people who respond here - it helps to hear someone other than our contractor.
I need some input on what my contractor is planning to do to identify our problem. The shower has not been used for four days, and the DensShield walls are drying out slowly. (Weather is cool and humid here, so AC and Heat aren't running much.) The contractor plans to apply "clear waterproofing" to the tile and grout joints, and caulk again between the tub and tile. He says if we still get moisture on the back of the DensShield when showering after doing that, it means the moisture is coming from somewhere else, not the tile installation. I'm not buying it, because I think the "waterproofing" is a temporary fix, and besides, the problem built up over four months so it might not show up the first few times the shower is used. Is my thinking correct?
He also says that as long as sealant was put between the tub and the DensShield, it doesn't matter if there is a gap between the two now. We still think they put a bead of sealant on the tub, then pushed the end of the densshield down into it, leaving the densshield touching the tub and all the sealant pushed out on the back.