Wet white marble shower floor turned gray!

TerzenOctober 25, 2013

During my bathroom remodel, I had Green Ming Basket Weave mosaic marble installed on shower floor. The pan was properly installed w/Portland cement, cured for a few weeks before mastic & tile was layed down. The white marble looked beautiful for weeks. I believe it may be thassos marble. After the plumber turned the water on, the tile darkened to a soft gray. After weeks, the outer areas of the floor returned to white color but the center area is still gray. I used a heat gun on a few tiles, they turned white but the next day they were gray. Could this be a moisture problem? We have tried blowing a space heater over the floor for 2 days, but no change. Has anyone had a similar problem? Thanks.

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I had/have the identical problem with our carrera mosaic shower floor. :( my tile setter blames the sealer and I blame the tile setter who can't articulate how he constructed the shower. It's being ripped out (at our expense). We tried everything to dry it out and after months it has not changed. So sorry to hear this has happened to you as well.

    Bookmark   October 25, 2013 at 8:14AM
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Find out EXACTLY how this shower was constructed. How do you know the pan was properly installed? (Just because they say so, doesn't make it true) What do you mean it was installed with portland cement? Did they REALLY use mastic? How was the shower waterproofed?

    Bookmark   October 25, 2013 at 9:02AM
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Catbuilder is correct.

"Portland cement" can be different things regarding semantics. But if they actually used a no-kidding honest-to-goodness STANDARD portland cement mixture, it's the wrong thing for a shower pan. It should have been "dry pack" or "deck mud", which is a sand-cement mixture with much more sand than cement, and very little water.

The difference between the two is that deck mud will allow water to drain or percolate through it.

If they used a no-kidding "mastic", again, that's the wrong product. Mastics can absorb water, hold water, and re-emulsify (soften) when exposed to standing water. And a shower floor will see standing water. A cement-based thinset should have been used to set the marble on the floor.

Again, it could be semantics at play. Some people erroneously swap "mastic" for "thinset". If your floor tile was adhered with something that came out of a re-sealable plastic bucket, it was "mastic" and it was the wrong product. If it came in dry powdered form and they mixed it up on site, then it was "thinset". Again, thinset should have been used.

Lastly, "the pan was properly installed". You already wrote that "The pan was properly installed w/Portland cement...". You didn't mention a topical membrane, so I'm supposing they used a CPE or CPVC membrane buried in deck mud?

Let's assume they used proper deck mud instead or portland cement. What they should have done is install a sloped layer of deck mud, with the slope going to the drain. Then install the waterproof membrane over the sloped deck mud. That way the membrane is sloped to the drain, and that is required by code. Then on top of the membrane, they install another layer of deck mud, that layer follows the slope of the membrane. Then the tile goes on top of that layer of mud.

If they installed the membrane flat on the subfloor and then installed a sloped layer of deck mud on top of the flat membrane, and then tiled? That's wrong, because you have a flat membrane.

A non-sloped membrane flat on the floor can hold water underneath the tile.

    Bookmark   October 25, 2013 at 11:27AM
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Three Apples- I'm so sorry you have the same problem. Our tile supplier is willing to replace the tile for free but I need to make sure it's not faulty tile.

Mongoct & Catbuilder - I will forward all your questions concerning the tile prep to my GC. We are not living in the house during remodel so I wasn't able to observe the applications but was assured their tile layer uses correct procedure for laying shower floor tile.

Tell me aint so, Mngoct, that if somewhere in the process an incorrect underlayment was used, the GC may have to pull everything out & start from scratch?

    Bookmark   October 25, 2013 at 3:54PM
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The thing is that what you are experiencing is not unique. Marble is a natural stone, it is porous, so water can move through it.

On the other hand, I also see installers using the wrong products, the wrong methods, etc.

Everything in your shower could have been done correctly, and it could simply be the choice of material; the marble.

There are also grades of marble that are better than others in terms of porosity.

I will say that whenever I see that anyone is going to use marble on a shower floor, I recommend that they use a topical membrane on the sloped mud underneath the marble. That puts the membrane right beneath the tile. Since the deck mud is protected by the membrane, there can be no deep wetting of the deck mud beneath the marble. With a topical membrane, if the marble does absorb water, it tends to dry out quickly.

    Bookmark   October 25, 2013 at 7:24PM
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Mongoct- here is copied response from our tiler:

"I used dry pack. Thinset(no mastic) and hydro ban. Did pre slope. Water proofed, then pan. Then tile with thin set. I have no idea what could be going on"

When we first noticed graying, we flushed the entire shower floor. It all turned gray but next day the outer perimeter whitened probably due to a steeper slope. Also, I soaked a surplus sheet of this tile overnight, & it never grayed. Go figure...

    Bookmark   October 25, 2013 at 10:01PM
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Terzen, we did the identical thing with a surplus sheet and ours didnt gray either. :(

Did you have this tile sealed?

I'm pretty close to getting a synthetic for our shower floor because I don't want to risk going through this again.

    Bookmark   October 26, 2013 at 8:34AM
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Threeapples- The shower floor hasn't been sealed yet as the plumber needs to return. Hmm, if your surplus tile didn't gray after soaking sounds like we both have the problem of what is going on underneath our tile. I'm checking now to see what color thinset our tiler used. If all the tile grayed & remained that way, I could live with it, but the partial graying makes my floor look dirty. We used Carrara in another bathroom & it's fine. Good luck on your synthetic floor; sounds like a good plan!

    Bookmark   October 26, 2013 at 1:26PM
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Mongoct - Our GC removed the drain cover, tiles & drain pack to see if weep holes were clear (which they were). Underneath the tile was wet & the dry pack layer was dry. The water must have gone through tile & grout (it was never sealed). My question to you is are you recommending a membrane between the two layers of deck mud & then another topical membrane directly under the tile? DH doesn't think the topical membrane would help since we need to find out why the moisture under the tile in center of shower did not evaporate after 3 weeks.

    Bookmark   November 1, 2013 at 1:46AM
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"My question to you is are you recommending a membrane between the two layers of deck mud & then another topical membrane directly under the tile?"

No, my previous wording was probably a bit vague.

What I recommend is really a method that I consider to be a "best practice" for showers, especially those with natural stone. Starting with a flat subfloor, after proper prep you put a sloped later of deck mud on the subfloor with a flanged drain set flush into the deck mud.

Then on top of the sloped mud you put a topical membrane; Hydroban, Kerdi, for example. Those at the two systems that have flanged drains.

Then you tile directly on the membrane.

The thing I like about the flanged drain is that when compared to a clamping drain, the physical structure of the clamping drain creates a small 1/4" high dam where the membrane is clamped by the drain's ring.

That 1/4" obstruction shouldn't restrict drainage, because the weep holes should allow any moisture that hits the flange to flow through the several sets of weep holes built into the drain. In the above photo, you can see the weep holes to the left and right of the 6 o'clock position on the flange. There's another set in the bolt holes.

The clamping drain system should work fine. But sometimes it doesn't. And sometimes there is no logical or apparent reason why it doesn't give optimal performance.

Compare that to a flanged drain, where the slope of the membrane is smooth from wall to drain pipe itself. There are no vertical obstructions.

I have to consider myself fortunate that I've never had "wet ring" moisture issues like you, stacy, and threeapples, even when using clamping drains.

One other comment. I hadn't seen this thread for a while and I just noticed your tiler's response to you:

"I used dry pack. Thinset(no mastic) and hydro ban. Did pre slope. Water proofed, then pan. Then tile with thin set. I have no idea what could be going on"

The part that confuses me is the "Did pre slope. Waterproofed, then pan."

I don't understand the "...then pan" part that follows "Waterproofed...". Is it supposed to be "Waterproofed the pan."? That would make sense.

With Hydroban, you do a sloped layer of deck mud. Then hydroban over that deck mud. No "pan" goes over that waterproofing. You tile right on the Hydroban.

I don't know what kind of drain he used. If he used the Laticrete flanged drain (which is designed to work with Hydroban) your GC shouldn't have been able to get to any "drain pack", here are the layers he would have found during his excavation:

If your tiler used a clamping drain with Hydroban, which he probably did since your GC was able to remove some tile and "dig through some mud to see weep holes", then he probably did it using the "divot method".

You do a mud preslope, then carve out a bowl or "divot" around the clamping drain.

Then hydroban the sloped mud, the divot, and the drain flange:

Then install the top part of the clamping drain over the base flange:

Then thread the drain grate assembly into the drain base.

Add a small handful of pea stone (or other "debris") over the weep holes so mud doesn't pack into the weepholes and clog them. Then fill over the pea stone to fill the divot with mud, then tile:

Sorry I can't be of more help, but it's time for me to run. Hopefully you can get things figured out.

    Bookmark   November 1, 2013 at 11:05AM
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Mogoct - I think tiler meant "waterproofed the pan." DH says according to your instructions & photos, our tiler did everything correctly. He thinks our marble is too porous & creates pathway for water to sit underneath it with no place to go. I'm afraid threapples is right & I will have to pick out another tile. I'll let you know how this is resolve.

Lastly, thank you for taking so much time (to include photos) in giving me such an informative response! I'm always humbled by Gardenweb members generosity & kindness in rallying round to help.

    Bookmark   November 1, 2013 at 12:48PM
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Even though I do not currently have a shower with this issue, thank you so much mongo for such a detailed and thorough explanation of waterproofing around the drains. It is really incredible to have someone with your knowledge patiently share that information with those of us outside of the industry. Thank you.

    Bookmark   November 1, 2013 at 2:13PM
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Some marbles can be like that. The global economy has been good and bad. There's so much more product out there, but some of it can come up short performance-wise.

You wrote that your marble didn't discolor when you soaked a sheet of it in water. That can happen sometimes. The tile by itself won't really absorb moisture. But once it's bonded to thinset, the thinset sort of wicks water over.

About the only other thing I'll write is that when using marble I'll use white thinset instead of gray. Some marbles can be a bit translucent and the white just performs better with a white stone like marble.

I do hope you get this resolved. Weird things sometimes happen.

I'm glad the photos and descriptions have helped.

Best to all.

    Bookmark   November 1, 2013 at 7:26PM
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Terzen, we are having another tile setter come and give us an opinion about our shower. I'm hoping to start demolition of its floor soon after and will take photos every step during "Excavation" in order to learn (hopefully) what went wrong and how to help lessen the chance of error the second time around. I'll post all we learn and our photos in case it might be of use to you or others here. I am really looking forward to showering in our own shower in this house already!!!!

    Bookmark   November 1, 2013 at 8:55PM
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Threeapples - It will be interesting to see what you discover during your "excavation." I look forward to the photos & the final reveal. Good luck!

Got a good chuckle from mongoct's last reply. There was a World Series? There is life after a remodel? Can't wait to move back home & take my first shower, too!

    Bookmark   November 1, 2013 at 10:07PM
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I see these issues with mosaic or basket weave too often.
But also there are many installs that it never occurs.
Seems to be a gamble on results. In all the cases I have seen it is the moisture from under the stone that is causing the problems. Its possible the moisture is coming in from so many grout lines and change of plane joints that haven't been caulked properly. Sealing stone in the shower stall is an issue as well. I think if the top of the stone has sealer applied it can make these issues worse.
I know everyone says you must seal your shower stall.
The sealer is breathable to some extent but will slow down vapor transmission or the evaporation of moisture under the stone. The only performance of an impregnating sealer is to temporarily inhibit staining.
What can stain stone in a shower stall.
Like mongoct said its all about the installation and specifying the correct product(s).
We also see from time to time white marbles that have turned yellow in wet enviroments. Something consumers should be aware that white marbles can have an iron content in their mineral composition . They are capable of rusting from prolonged exposure to moisture. Again something a sealer cannot prevent. Thank you mongoct for a great explanation of pan construction and the pics!

    Bookmark   November 3, 2013 at 9:46AM
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I just started an install of White Carrara 3 x 6" marble for my kitchen backsplash in a subway tile set. I have experienced the same problem - once tiles began to absorb the moisture from the thinset, they have changed color. Any grey veining has turned really dark grey and some of the white tiles are now this awful yellow. I have been reading several blogs and realize it is likely due to iron oxide or pyrite mineral within the tiles. My wish was for a beautiful WHITE with subtle grey veining and cherry-picked each tile to obtain that. However, now I am ready to tear out what has been set. I'm considering changing to a ceramic tile to avoid this hassle. Any ideas from anyone?

    Bookmark   June 12, 2014 at 10:27PM
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I'm considering changing to a ceramic tile to avoid this hassle.


    Bookmark   June 13, 2014 at 12:33PM
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What a shame that the thinset changed the color of the marble tiles. Why don't we hear about this more, given the popularity of marble tile backsplashes?

Could they be sealed first, the way people seal crackle tile to prevent grout migration into the crackles?

    Bookmark   June 13, 2014 at 12:42PM
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The grey portland ceement crystals will still grow into the marble and darken it.

Sealant isn't armour. It simply gives you more time to clean the tile and grout.

    Bookmark   June 13, 2014 at 7:08PM
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