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Unread 06-16-2020, 10:13 AM   #1
jim_d
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Need some help - water penetration under floor tiles

Hi folks,

So I completed a custom shower build - porcelain tile over kerdi board, preformed kerdi shower pan with ditra heat, and kerdi line drain.

Grouted using mapei Ultracolor+ FA.

After a week of use, I am seeing discoloration around some of the grout joints (Pic attached). I did not seal the grout, as the Mapei instructions indicated that doing so was not necessary, although I now realize I should have done it anyway. Still this seems odd to me that this would happen in just one weeks time.

Just wanted to get the community’s thoughts on this and hopefully some advice. I am assuming the problem is water penetration at the grout joints, but I am uncertain. I’ve been running a dehumidifier and plan to continue doing so to help dry it out (if this is actually the problem), then either seal the grout or possibly regrout the shower floor altogether.

Has anyone run into something similar and if so, any recommendations on how to proceed? Is there anything that could be causing this other than moisture? Thanks.

* just a note on the picture - the gray discoloration is not water on the surface - the tile is bone dry here.
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Unread 06-16-2020, 03:43 PM   #2
Tiger Mountain Tile Inc
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Not unusual and there are a good amount of threads here with similar issues.

Unfortunately, this seems to be a thing with natural stone over bonded waterproof membranes such as the Kerdi system. My guess is that you have a very slight depression there in the middle. With overlaps on the edges and an overlap for the drain it would make sense.

I don't really think there is a cure for it and this is why I discourage my customers from using natural stone in a shower.
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Unread 06-16-2020, 04:57 PM   #3
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Jim, I believe he says it's porcelain but it's doing the same thing natural stone does. To me, looks like the clay is absorbing water and showing thru the glaze.

Some people say these type showers dry out after each use. You can see that's not so. Not all porcelain tiles would show moisture thru the glaze like that. The moisture would still be there but it wouldn't show thru on maybe a different color tile. Seems like every time we have a thread on this problem, it's with white tiles. I don't think sealing will help long term.
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Unread 06-16-2020, 04:59 PM   #4
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Is the Ditra Heat also in the shower? Did you cover it with Kerdi? While the membrane is waterproof if you deal with the seams correctly, it will hold water since it can't get over the top of the towers and flow out.

A sealer won't help this issue. It isn't waterproofing, it's job is to slow absorption of things that can stain so you can clean it up prior to it soaking in. There will be a little water resistancy for a short while after installation, but that doesn't last and is not total.

The slope on the preformed pans relies on the floor being perfectly level prior to installation, otherwise, all bets are off.
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Unread 06-16-2020, 05:28 PM   #5
jim_d
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To confirm, yes these are porcelain tiles, not natural stone. And yes, I put ditra heat in the shower and covered it with kerdi as prescribed.

I’ve had the dehumidifier running nonstop on full power for 24 hours at this point. I also turned on the ditra heat, hoping that would help speed the drying process. So far, no improvement in the discoloration.

I know that some moisture is expected through the tile and grout. I’m just very surprised with this result after only one week of use. Is it possible that there is a problem with the tile? Am I wasting my time trying to dry it? I guess ultimately I’m concerned about too much moisture/mold growth between the tile and waterproofing.
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Unread 06-16-2020, 08:51 PM   #6
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Mold requires three things:
- moisture
- food
- the spores themselves

There's no food in Ditra or unmodified thinset

Moisture is tougher

Spores, probably not, but with no food, they won't reproduce.

There will be some that catches on the grout.

You didn't answer whether the floor was perfectly flat prior to installation of the pan...
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Unread 06-17-2020, 05:24 AM   #7
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Yes the floor was level.
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Unread 06-17-2020, 08:39 AM   #8
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Quote:
Originally Posted by Davy
Jim, I believe he says it's porcelain but it's doing the same thing natural stone does.
Thank you and I missed that. This is an odd one then. Jim, do you have any information on the tile that is installed? It'd be nice to look up the specs if there are any.
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Unread 06-17-2020, 09:50 AM   #9
jim_d
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Link to the product is below. The 12x24 glossy version was installed.

https://happy-floors.com/products/alaska/
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Unread 06-17-2020, 01:10 PM   #10
Lou_MA
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What size trowel did you use to set tile?

Did you trowel in one direction only?

What brand thinset?

Did you pull tiles to verify coverage? Adequate coverage meaning notches were fully collapsed and 95% of tile supported.
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Unread 06-17-2020, 03:29 PM   #11
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It's REALLY hard to get the required minimum thinset coverage on a large format tile like that. At 12x24", that's a rigid rectangle of 288sqin. If you weigh say 150#, that's barely 1/2# per sq in when you press down on the tile. To collapse all of the trowel notches, you'd have to shuffle that tile back and forth a LOT.

It sounds like you probably do not have the minimum recommended thinset coverage on the back of the tile, allowing moisture to accumulate in the spaces.

On a wet surface like the shower floor, the spec calls for 100% of the edges and at LEAST 90% of the rest of the back of the tile to be fully covered in thinset.

Over a waterproof membrane, you can't now pull one up and check without lots of other damage although you need to do that when laying the tile at least periodically to verify you're getting proper coverage for the tile, the thinset, and your technique.

The Europeans have been using a slant-notched trowel for awhile now, and they are available here if you look. Same amount of thinset for similarly sized notches, but the shape means that they are tall and narrow, and literally fall over flat after you've combed out the thinset. MUCH easier to get the full coverage on the back when you use one of those.

I was in a class and we were setting clear glass tile. These tile were like 4x8" and it took a lot of pressure and moving back and forth to work all of the thinset flat underneath.
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Unread 06-17-2020, 05:15 PM   #12
jim_d
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Definitely a lot of thinset required to set these tiles - yes, I periodically checked coverage aiming for 100%. Thinset used was mapei kerabond-t.

Used directional troweling technique with a euro notch trowel. Just as Jim described, I selected that trowel because it is supposed to allow the ridges to collapse more evenly and is ideal for large format tiles. I really don’t think tile coverage is the issue here. I was pretty careful about it.
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