Grout in shower floor discolored - tile experts please weigh in!

PipdogAugust 13, 2012

Our shower floor was installed middle of last week and was grouted on Thursday. The grout color is a very light gray (Winter Frost - C-Cure), but after a day or so, the grout in the shower floor has taken on an inconsistent, discolored look. It is particularly darker around the drain and is covered with a white, chalky substance. The floor material is Calacatta marble. Unfortunately, the hex marble almost looks like something is eating away at the tiles, as the edges look jagged. This is getting worse over time and after a few days, it does not look like a brand new shower.

My contractor is off for a few days, but we have been researching this and came across a few older threads about inadequate sloping, weeping, and pre-sloping. Our contractor subbed out the hot-mopping and tile installation, and I would expect we will need to meet with all of them to determine what is causing is.

But based on these photos and the fact that the shower has never been used (the shower head was installed on Saturday afternoon and it was turned on briefly to make sure it worked properly), does anyone have any thoughts as to what could possibly be causing this?

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You shouldnt use the shower right after it was grouted it needs time to cure

    Bookmark   August 13, 2012 at 10:14PM
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The shower was grouted on Thursday morning and the shower head was installed on Saturday afternoon. So it cured at least 48 hours. Is that not enough time for the grout to cure? Also, what's strange is the other tile that got wet in the shower (on the walls) looks fine.

    Bookmark   August 13, 2012 at 11:05PM
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We're not entirely sure, but we think the sub used a mortar mix as opposed to a sand mix. For those that are experienced with tile installation, does this look like lime precipitating out via the joints?

    Bookmark   August 13, 2012 at 11:28PM
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That was going to be my question...what did he use for the mud bed.

When the thickness of the mud bed gets wet, a portion of the drying occurs upwards via evaporation. You have porous grout. Minerals can be carried upwards with the moisture through the grout, and when the water evaporates, it leaves the minerals behind: efflorescence.

Lime in the mortar mix could exacerbate the problem.

Having the hot mopping done on a flat surface slows water movement out of the mud bed and down the drain. That is a negative too.

    Bookmark   August 14, 2012 at 1:21AM
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thanks, mongoct. If the mud bed is indeed mortar, would our solution be ripping up the marble and laying a new sand bed? I've read that efflorescence can generally be a temporary condition that may diminish over time as the soluble salts work their way out of the substrate and setting system. But this is not based on experience, only from what I've read online.

    Bookmark   August 14, 2012 at 10:53AM
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Pip - has the tile setter returned to cleanup the grout and seal it? Our contractor is waiting 72 hours for everything to dry/cure and then he will do the final cleaning and seal the grout and marble.

    Bookmark   August 14, 2012 at 11:07PM
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The tile setter hasn't returned yet -- he's on another job and isn't available until Sunday, so it will be more than a week after he's grouted. We'll see what happens. Thanks for your reply.

    Bookmark   August 14, 2012 at 11:32PM
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