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Old 02-17-2018, 10:49 AM   #1
Dor
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Have Tried Everything- Black Spots

Please take a look at the attached photos. I have tried every type of cleaner to no avail- Tilex, Clorox Bleach gel, Soft Scrub, and Laticrete. Black spots have shown up in the grout of my porcelain mosaic shower tile floor. I keep it very clean, and we have ventilation.

Lately, these spots have been showing up in increasing numbers, and I'm not sure what to do. The shower was installed about 2 1/2 years ago. The black spot issue started to appear about 4 months ago. The grout was sealed right after install. I haven't sealed it since. Should I go ahead and reseal so that I don't get more black spots? Is there something that I can do about these before applying sealer? Thanks in advance for your help!
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Old 02-17-2018, 12:51 PM   #2
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To me, those dark spots look more like gray thinset than anything else. I would dig at it with a screwdriver to see if the dark color continues deeper.

Do you know how the shower was installed? A pan liner system or a surface membrane type system?
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Old 02-17-2018, 02:25 PM   #3
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Thank you for replying. I do not remember the particulars of how it was installed. I think there was some type of membrane, but I can't recall exactly. If I dig into it with a screwdriver, what am I looking for? How much grout would I be removing?
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Old 02-17-2018, 05:59 PM   #4
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I would dig down about 1/8 inch. If you have a surface membrane under your tiles, then the tiles will be bonded directly to the membrane and you will not want to dig down over 1/8. You don't want to poke a hole in the membrane. But, If you have a pan liner system, then you'll have a mud bed under the tiles and the membrane/liner will be below the tiles about 1 to 2 inches. I would dig down 1/8 right on one of the dark spots to see if the dark color continues. I'm thinking that they may have used a notch trowel that was too big and thinset was allowed to get too high between the tiles.
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Old 02-18-2018, 10:03 AM   #5
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I agree with Davy that it looks like gray bonding mortar that wasn't cleaned away enough (between the tiles) after tile installation and the grout was installed in such a thin layer to cover it that it's slight deterioration is now showing the mortar. After the tiles were installed and before grouting, the mortar should have been cleaned away so that a majority of the grout joint between the tiles could be filled with grout.

To confirm I would slightly pick at a tiny spot anywhere along the perimeter of the dark spot. If you can pick away a little spec of grout and you see a darker spot below, you're looking at the gray bonding mortar used to set the tile.

And if that's the case, you could use a grout removal tool to grind down into the joint about 2/3rds the depth...then fill that area back in with grout.

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Old 02-18-2018, 10:10 PM   #6
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Hi Davy and Tonto,
So it looks like it is the mortar showing through. I'm not handy at all and will have to try to find someone to hire to do the job. Will I be causing damage if I leave it as is and continue using the shower for a while? Also, is there anything particular that I need to make sure the person I do hire does/knows how to do?
Thanks so much!
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Old 02-18-2018, 11:38 PM   #7
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Won't hurt a thing for it to stay like that.

Unless you're OCD, and then the world will come to an end.

You could probably get at it with a utility knife, as long as you're careful not to dig too deep, on the chance there's a membrane directly underneath.
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Last edited by Kman; 02-19-2018 at 03:47 PM.
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Old 02-19-2018, 11:20 AM   #8
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I'm assuming Kevin means membrane instead of membership. If not I'm not getting the humor.
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Old 02-19-2018, 03:48 PM   #9
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Yeah, membrane.

Stupid autocorrect.
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