LESLIE: Paul in Hawaii has got a leaky bathroom. Tell us what’s going on.
PAUL: Yes. In my master bathroom, there’s a granite countertop sink with – it’s a countertop with two sinks. The left sink, underneath the cabinet, constantly has a strong mildew smell. Now, I’ve got the back of the cabinet out to check the drywall. No leaks. I’ve cut a hole in the floor of the cabinets to look at the concrete. No leaks. I don’t know where it’s coming from. I’ve got a bucket right now of those crystals that absorb moisture. The thing is full of water. I mean I’ve had a friend of mine who’s another contractor – I’m also a contractor – and we can’t figure out what’s going on.
TOM: So you have high humidity in this cabinet, is that what you’re saying?
PAUL: Yes. High humidity in the cabinet. I live in a very dry area so it’s not like there’s moisture in the air from the outside doing it. I don’t know. I don’t know what’s causing it. I …
TOM: And you’re on a slab?
PAUL: On a slab floor, correct.
TOM: Slab floors are very hydroscopic. They pull moisture up from the dirt, up through the slab and into the cabinetry itself. You might just want to think about venting this cabinet. Have you ever left the doors open for a week to see if it made a difference? Because I bet it would.
PAUL: It does. It actually does.
Now, here’s one thing I must tell you: there’s an outdoor shower on the opposite side of that wall but it’s all granite, sealed to the tile. So I can’t imagine how it would be coming in from that side but anything’s possible.
LESLIE: Yeah. But could it just be a condensation issue, like when you’re running cold water and the warmth and humidity of just being in Hawaii, moisture forms on the cold-water pipes, drip, drip, drip?
PAUL: I don’t think that’s it. It just doesn’t seem to – that doesn’t seem to be the problem. The only thing I can think of, somehow moisture is, like you said before, is coming underneath the ground and up into the cabinets somehow. I guess that’s probably what’s happening and (audio gap) how to solve that. Your idea of venting that cabinet is probably a really great idea and there’s a way I could do that. I could put a small, round vent in the – to the outside from that cabinet wall there.
TOM: I think it’s moisture that’s coming up through the cement slab and it’s congregating in this unconditioned space of the cabinet. And it’s building up to the point where you’re noticing it vis-à-vis a moisture smell, which you’re calling mildew. And I think if you vent the cabinet, that that’s going to go away.
PAUL: Alright. Well, listen, I’ll definitely consider that venting. That was a very good idea. Thank you for taking my call.
TOM: You’re welcome. Good luck with that project. Thanks so much for calling us at 888-MONEY-PIT.
Is the gap at wall and pipes supposed to be sealed under bathroom sink. Feels warm in the cabinet and there are large gaps.
Yes, that would be best practice. Probably not having a big impact though.
The air in our laundry room sink under cabinet is humid only in the hot summer months. We live in Coastal NC in a home built on a slab. There is evidence that water was absorbed in the particle board floor of the cabinet by a large volume of water. Could it be that the increased air temperature and humidity in summer lead to the release of the moisture absorbed in the particle board to the unconditioned air in the cabinet? When we leave the door open, the humidity in the cabinet does seem to dissipate, just as for Paul in Hawaii.