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Moisture+Mold under tub with hole in foundation


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Background: I have a 1950's ranch home that I've been busy updating. I finally got around to looking at a "stinky" closet that we assumed was ammonia from cat urine (the prior owners let the cat sleep in there). Anyways, I discovered this weekend that it's actually coming from our guest bath. The closet has an access panel in it, and after I pried it off I discovered a lovely petri dish underneath and it was very humid inside. The prior owners had zero caulk around the tub rim (which I took care of several months ago when we moved in). I ran the tub and shower and can't seem to find any leaks... yet it still is very moist and damp under the tub.

 

Also, our foundation has a hole in it and the dirt from under our house is just sitting under there (like a 2ft/2ft hole). Research online tells me that this was normal when they poured foundations to allow for the plumber to install the tub later.

 

So here are my questions:

 

1. Isn't this hole in the foundation a great way for potential rodents/bugs to get inside... as well as moisture?

2. Should I put a vapor barrier or something over the hole? The drain for the tub drops directly into the whole, where there's a p-trap and then pipe that disappears under the house into the dirt.

3. I sprayed bleach on everything, but is the mold something I should be concerned with and get a remediation company out? I've heard the whole mold thing is overblown... so don't know.

4. My neighbor told me his house is the same way and they have a stinky closet as well. Is this just a design flaw of older 1950's homes?

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The opening for the tub drain can be found in pretty much any slab foundation.

 

Likely what you are calling "mold" is just the smell of damp earth. If you have a high water table there, the soil in the tub drain area will be damp. The only rodent that can come through there would be a mole. However termites love tub drain areas. Its damp and there is yummy wood to digest. 

 

It might also be damp there because your tub drain is leaking. 

 

You can put some plastic down, and cover it with gravel. I wouldn't pour concrete in there, since someday a plumber might need to service the tub trap/ drain. 

 

 

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Thanks, I was thinking about putting plastic down with some rocks around it. I just wasn't sure if concrete would be better but you bring up a good point. I'm positive I do have mold underneath (some black stuff growing, other was white). Do you suggest I hire a remediation company, or just bleach it down, (maybe paint some killz over it)? I can't seem to find an actual leak on the tub anywhere so the wet dirt theory makes sense.

 

 

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We got that same musty smell when we pulled up our flooring from the slab during a redo.  Once the vapor barrier was down it went away so if you can do that you will most likely eliminate the smell.  Personally, I'd spray a little bleach wherever I could to kill the mold, let is air out for a while and then put in a barrier of some kind.  Afer that you can buy some Damp Rid to eliminate lingering moisture and then just monitor it a while to make sure there are no leaks.  The biggest worry here would be that termites might come up and start eating the wood.  You might have an exterminator come check it out before you lay down the barrier as they can put some strong termicides in and around the hole to prevent infestation.

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Mold needs a medium to grow on, so unless the mold is on the back of the sheetrock or on wood, its not mold. Its not going to grow on the bottom of the tub or on bare concrete. Lowering moisture content is key. Seal off the soil exposure and let the area dry out. Can't hurt to shop-vac under the tub. There are folks who create screened openings to their tub drain areas, but I think that is overdoing it. 

 

Chances are if you haven't had any termites there, they aren't likely to show up now. Its quite possible that chlordane (now banned) was sprayed at the tub drain and that has kept them out for the past 50+ years. But you might still want to get a termite checkup on your whole castle, just in case.

 

Make sure there are no leaks below the tile around the perimeter of the tub. Blast the showerhead and look for drips.

 

And BTW, gentle readers who do not have tub drain accesses (especially first floor), the code does not require one if the tub drain is hard pipe (no slip joints). Hence COH does not require one. West U does. Bellaire does. What do they know? 

 

 

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Thanks everyone. Yes, innerlooper, the stuff is growing on the studs and some sheetrock. No termite problems for the past 50 years (had it checked when we bought months ago). What do you mean by a "screened opening" to the tub drain area? Do you mean like a screened vent on the exterior wall of the house? I think I'm going to take the first steps of getting it completely dry and sealed. I'll then look for any other leaks and I like your idea of sealing the thing up. Drywall is easy and I don't mind having to cut it open later down the road if I need access.

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Screened opening to the living area (closet usually) so that conditioned air will keep the area under the tub dry. 

 

After you have stabilized the mold or whatever, let it dry and maybe spray kilz on it to seal it in, if you can reach there. 

 

I would seal off the dirt with plastic and gravel, and leave a weatherstripped wood panel door for easy access. Don't rock it over. 

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Great suggestion. Last question then... When I seal off the dirt w/ plastic, how do I "seal it" when I have a drain pipe going down the middle of the hole? I assume it needs to be airtight so would I take a square sheet of plastic, cut a slit from the outside to the center, wrap around the pipe (maybe tie rope around the pipe to hold the plastic tight to the drain pipe?) then overlap the plastic on itself and tape it along the seam (filling w/ gravel on the edges to hold the side down)?

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It doesn't have to be hermetically sealed. I would take one of those heavy duty contractor trash bags and cut it up, of if you have some heavy clear plastic (old shower curtain?) be creative and cut out for the drain, apply several layers, etc. Then cover with gravel or sand and that should seal most of it. If the soil is uneven, you can trowel it so it is somewhat level, first clear debris, rocks, etc. 

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Mold needs a medium to grow on, so unless the mold is on the back of the sheetrock or on wood, its not mold. Its not going to grow on the bottom of the tub or on bare concrete.

mold can easily grow on concrete. if you think otherwise you are mistaken.
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