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Bill V. & others- Help! Dark spots on new tile and grout?

Posted by Anna_123 (My Page) on
Mon, Oct 29, 12 at 20:21

We are having some real problems with dark spots on the floor of our new shower. Background- Marble tile, unsanded grout, Schluter Kerdi system, floor was sealed before first use, been using the shower for approx 6 weeks.

Almost as soon as we started using the shower, we began noticing that the grout in some areas was darkening a lot and also not lightening back after 24 hours, even with a fan. It now has lots of dark spots (especially around the drain) and looks mottled in some areas. It also looks like the tile itself is darker in those spots where the water hits most often and there are some cracks in the grout, though not everywhere. It continues to get darker the more we use the shower.

The worst part is that this is the second time we have had this exact problem with this same shower, tile, and grout. The first time our contractor subbed the work out and the guys were not the best, so he assumed they did something wrong (plus they didn't use Kerdi that time and they didn't seal it), so he ripped it all out and redid it. That was about 6 weeks ago and we already have the same problem but no idea what is causing it. Please help!

This pic is right next to the drain


Follow-Up Postings:

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RE: Bill V. & others- Help! Dark spots on new tile and grout?

Close up of another area


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RE: Bill V. & others- Help! Dark spots on new tile and grout?

And a pic of the entire floor.


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RE: Bill V. & others- Help! Dark spots on new tile and grout?

I will be interested to hear what Bill V and others say. I too used the kerdi/schluter system (pan, drain, water/vapor proofing) and will be using unsanded grout on the walls. regular grout on the floor with porcelean tile. Same drain as you.


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RE: Bill V. & others- Help! Dark spots on new tile and grout?

Did he do a traditional mud pan or use the pre-formed Schluter floor pan? Looks to me like a poorly-sloped mud floor. If that's the case, I suspect there are "birdbaths" that allow standing water under the tile in the dark areas.

Check the slope from the drain with a small level. If you don't have a healthy slope, there's your problem. You need a MINIMUM of 1/4" per foot from drain to walls.


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RE: Bill V. & others- Help! Dark spots on new tile and grout?

Aside from the problems you are having, I love your floor! I'm a big fan of hexagons, and the color variation is wonderful.


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RE: Bill V. & others- Help! Dark spots on new tile and grout?

StoneTech- I am pretty sure he used the preformed Schluter pan this time, though the first time it was a traditional mud pan and we had the same problem. I don't know what the slope is, so I will check that out tonight.

Williamsem- Thank you! I love the tile (we also have the larger marble hex on the main bathroom floor). This was really supposed to be my dream bathroom, and I'm trying not to let this whole drawn out mess affect how much I love it :)


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RE: Bill V. & others- Help! Dark spots on new tile and grout?

Anna 123- I don't have an answer for you but I do have a question if I may get your input. We have a shower that we will be having to replace with the Kerdi system. Currently we have a traditional mud pan which we've had problems with mildew. My question is what is involved with tearing out the old to replace with the new system? Is just the floor taken out or is the whole shower gutted? Thanks so much.


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RE: Bill V. & others- Help! Dark spots on new tile and grout?

Generally best to start with a "New Slate." It's difficult, but not impossible to just remove & replace the floor. At the very least, you would need to remove also the first row or two of wall tile so that there would be some hope of tying in the waterproofing wall system with the floor system. Much depends on exactly how the shower was waterproofed. Was it done with plastic sheeting or tarpaper on the studs behind the wallboard ....or was a surface applied membrane like Kerdi or Hydroban used on the face of the wall surface? Do you have matching, replacement wall tiles? If not, it will probably look like a patch job.


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RE: Bill V. & others- Help! Dark spots on new tile and grout?

sis2two- When the contractor redid this shower floor, he removed the floor and the bottom couple rows of wall tile.

SonteTech- Contractor did use the Kerdi membrane when he redid the tile 6 weeks ago. He is pretty adamant that the installation was done above and beyond industry standards, and that this is a product issue. I don't know if that's accurate (and I have someone from the tile shop coming out tomorrow to take a look), but either way we don't want to start over again without figuring out what the problem is and how to avoid it again. There is a slope to the floor and no water pools after a shower, but I don't know for sure what the actual slope is.


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RE: Bill V. & others- Help! Dark spots on new tile and grout?

Thanks Anna. I hope you will find out what the problem is soon and be able to remedy it. Good luck!


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anna-Did you find out anything yet?

Have been wondering if you ever found out anything about your shower?


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RE: Bill V. & others- Help! Dark spots on new tile and grout?

Been watchin' this at "JB," and I think that possibly you have SOME tile that is more conductive to "Water Entrapment," in other words, this marble MAY be more porous than the rest and absorbs more moisture and is, therefore darker. I dunno....just a thought.


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RE: Bill V. & others- Help! Dark spots on new tile and grout?

I'd prefer that more grout had been left in the joints. They look dished out a bit too much, where too much grout was removed during the cleanup phase. I'd have preferred the grout to be more flush with the face of the tile.

Looking closely at the first two photos, the darkened grout lines are all parallel to one another. In the first photo you can see the wet grout lines are all parallel to the edge of the drain. That leads me to believe that the "uphill" edges of the tiles are acting like mini dams and holding water, they are preventing water from easily flowing downhill to the drain.

The second closeup photo, you see the same effect. All the damp grout lines are again parallel to one another. Again, to me that reflects a drainage issue. Not necessarily with the amount of floor pitch, but with the grout lines being so dished out that they hold water and slow drainage.

Marble is porous and can absorb water. With the grout lines being a bit too raked out, the edges of the marble hexes are exposed. Water held against the tile edge can lead to absorption into the marble.

The crack in the grout in that second photo, you also wrote that there are other cracks. That's usually a sign of too much water used in the grout mix, or that sanded grout should have been used instead of unsanded. Unsanded should be used in joints less than 1/8" wide.

Cracks can also indicate movement in the floor, but that shouldn't be an issue with a properly set Kerdi Tray.

As far as him having used a preformed Kerdi-Tray, if he did, it appears that is was certainly cut down in an awkward manner. The drain is no where near centered in the shower. So if he did some filling here and there with mud or thinset to even out the floor pitch or edge elevations, that could have be part of the problem. But that's supposition on my part.

About the only other thing I could question is that often times with small tiles, when the sheets are set into the thinset, thinset can ooze up between the hex tiles and partially fill the grout lines. That thinset needs to be cleaned out so the grout lines can be completely filled with grout. If it's not, you can get uneven thicknesses of grout, think of it as a veneer of grout over a blob of thinset. That can result in uneven water absorption, the grout cracking, etc.

All that aside...with this being your second go-around, he should have install the sloped Kerdi Tray and thinsetted it to the subfloor. Then he should have set the Kerdi drain. Then he should have thinsetted Kerdi Membrane (an orange colored sheet material) over the Kerdi Tray, then tiled on the Kerdi Membrane.

I'd be interested in how he tied the Kerdi Membrane in with the wall membrane IF he used Kerdi Membrane over the Kerdi Tray.

Best. Mongo


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