How to address mold under shower floor tile?

last year

last modified: last year

Hello,

I noticed some grout between my shower floor mosaic tiles has broken away and dirty soapy water has presumably been seeping under these tiles for years. Any advice on how to address possible mold growth or other concerns under the tiles before re-grouting? Should I just pour white distilled vinegar in all crevices and let it sit/dry out over a couple hours?

Thanks,

James

Featured Answer

millworkman

last year

Tile and grout are not 100% waterproof, nor were they indtended to be. That is why it is imperative that the pan and walls be built correctly. If the pan is pitched properly and drains accordingly you should have no issues with mold.

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Comments (9)

Sigrid
last year
The real concern is moisture and rot. Wood (probably your subfloor) tends to rot under the conditions that cause mold.
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James Lee
Original Author
last year
last modified: last year
@Sigrid

I believe my floor tiles are installed on a hot mop shower pan for waterproofing, so I was more concerned about mold born out of dirty shower water sitting under the floor tile for extended periods of time. Not 100% sure if that's a real problem though.
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PRO
Minardi
last year
last modified: last year
If there is mold under the shower floor, then it is not built correctly. Probably hot mopped without a preslope, so the pan is sitting there like a rancid fish tank and not draining the water out. A properly built shower has a mud pack preslope tied into the walls, then the whole thing is hot mopped. Not just the pan. If the walls aren't waterproofed as well as the pan, then you get water passing through them, back into your walls, and draining down under the pan area, and the rest of the bathroom and house.
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dan1888
last year
Chorine kills mold.
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PRO
Minardi
last year
NO, chlorine bleaches mold. The roots are still there. As is the root issue of the whole problem, which is the incorrectly built shower.
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James Lee
Original Author
last year
last modified: last year
@millworkman I'm wondering how shower water that seeps under the floor tile manages to drain? I thought drainage happened from above the floor tile and didn't realize it can happen from below as well?

@Minardi I attached a photo of my admittedly very ugly shower that I'm looking to clean up. There is sloping towards the center drain, so presumably there wouldn't be mold under the floor tile, but I am not certain. To be extra safe, should I pour white distilled vinegar in all crevices and let it sit/dry out over a couple hours?
PRO
Minardi
last year
Vinegar destroys grout. Never use vinegar to clean anything. If you want an inexpensive mold cleaner, then Concrobium is it. But, that doesn't fix the problem of the waterproofing layer being flat on the floor and not sloped.
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millworkman
last year
"I'm wondering how shower water that seeps under the floor tile manages to drain? I thought drainage happened from above the floor tile and didn't realize it can happen from below as well?"

That is why it is important to know how the shower was constructed, the details are important as well as that the pan was flood tested. Grout as I mentioned was not ever intended to be waterproof. the drain would have openings below the tile as well which is why the proper pitch is imperative in the shower pane
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