I've had the same problem with our bathroom. The contractor thinks it was the underlying tile adhesive seeping through. He re-grouted several times, but it never got better. Not quite sure what the true cause was/is.

It could take a week or two for the cement-based thinset to fully cure/dry.

Blotchy colors can be due to myriad issues. From an uneven mix if multiple batches or bags were used, to too much water used when mixing the grout or too much water used during clean up. Usually too much water.

Thanks so much for the responses. Our contractors did use two batches of the same grout, but the darker patches are spread throughout the room, so perhaps it's the too much water thing.

So should we just wait it out another week or until they come back on Tuesday? I can't imagine digging out the grout to replace or fix it...there's just so much of it with the 1" hex. Maybe grout stain?

So should we just wait it out another week or until they come back on Tuesday? I can't imagine digging out the grout to replace or fix it...there's just so much of it with the 1" hex. Maybe grout stain?

Let them know of your concerns now. If it is moisture-related, the amount of moisture under the tile can be dependent on what's under the tile; thinset, or a thicker setting bed, for example.

If the patches of darker color are moisture, the size should shrink over time. You can mark the edges with blue painters tape placed on the tile (not the grout). See what happens.

Sometimes dark gray thinset can wick into light grout, darkening some areas. Depends.

Light "powdery" areas can sometimes be efflorescence. That doesn't sound like your issue.

Some discoloration can be caused by minerals in well water or even treated city water. Oh, the possibilities!

Let the installer know to start a timeline with them, see what they say. But unless it's an obvious mechanical or installation error, I wouldn't touch the floor for a couple of weeks.

Thanks so much, mongoct.

So are you saying that some of the thinset they used to adhere the tiles to the subfloor could be coming up through the grout?

We have talked with our contractor about it already...he said it could be some dirt/etc. from the rest of the remodel and wants to wet down the floors when they return this Tuesday. We do have pretty hard water here and high iron content, I believe.

Back in January, they installed the same tile and grout in our hall bathroom with no issues at all. The room is much smaller (about 6x9 vs. 10x10), but the grout is uniform through out.

Re: Thinset...some of this stuff sounds sort of voodoo-ish, but...

If an excessive amount of thinset creeps into the grout lines during tile installation and the thinset partially fills the grout joint, and the excess thinset is not raked out prior to grouting...

1) The light grout can be sort of "stained" by the darker thinset, especially if the thinset isn't fully cured.

2) Even if the thinset is fully cured, if the thinset fills part of the grout joint and the grout becomes a thin 1/8" or so veneer over the thinset, then the darker thinset can sometimes shadow through the lighter grout.

If using a light colored grout, I'll usually use white thinset instead of gray thinset.

This topic is so full of if's, and's, but's, and maybe's.

Sometimes something bad simply happens, despite the best of intentions during installation.

If water quality is an issue. I don't use water from the building site. I'll bring my own, or use bottled distilled water.

An aside: Although it should not have been used and most likely wasn't, if a mastic is used to set the tiles instead of a cement-based thinset, then all sorts of issues can arise. The mastic can bleed into the grout, and if natural stone tile is used instead of a porcelain or ceramic tile, the mastic can bleed through the stone too.

Good news is that your guys are willing to take a look at it instead of giving you the "that's normal" reply.

Yes, our contractor has been a "stand-up" guy so far. He definitely takes concerns seriously. I'm almost positive they used a cement-based thinset. I asked for a light grey grout, so perhaps your thinset theory is at play here. I'll bring it up as a possible explanation.

Thanks again for your insight!

1) The light grout can be sort of "stained" by the darker thinset, especially if the thinset isn't fully cured.

2) Even if the thinset is fully cured, if the thinset fills part of the grout joint and the grout becomes a thin 1/8" or so veneer over the thinset, then the darker thinset can sometimes shadow through the lighter grout.

What it is, is that if there's an extreme difference in the depth of the grout joint (as Mongo said, if it's just a veneer of grout over a joint almost filled with thinset, next to an area where the grout joint goes almost all the whole thickness of the tile), the "veneer" area is going to dry faster than the area where the grout is full depth. This will cause a difference while it dries, and as Mongo said, it could take a couple of weeks to dry completely. Don't try wetting it or wiping it at all-- that'll just prolong the problem, if this is it. Wait another week, and if it still looks uneven, call your guy back to cut out the areas that don't look right. Keep in mind this may aggravate the problem even more (being that it's not being mixed at the same time as the rest of the grout. Either way, once again, you won't know for a couple- few weeks.

Thanks bill! Will do.