Stone Tile Gurus - Granite Darkened After Mortaring

OrchidOCDOctober 24, 2011

Cross-posted from Flooring, because I'm not sure which forum Bill V and Mongo (the BR and tile gods!) check most often - this forum seems more active. :-)

Hello Stone Tile Gurus,

Yesterday I laid my first self-installed granite floor - moderate size bathroom, 1/16" spacing for 12" x 12" Beige granite tiles - and the tile darkening that I assumed yesterday was just due to the tiles absorbing fluid from the thinset has only lightened marginally in the past 24 hours. I used Mapei white unmodified tile mortar (thinset) mixed with Mapei Keraply latex additive (instead of water) to get the (hopefully) strongest bond possible to the substrate. I was careful to select white, not grey, thinset to insure that the natural stone color wasn't darkened.

The lippage is minimal, the grout lines pretty well straight with the 1/16" spacing, and the thinset seems to be cured from the little I can access between the grout lines and at the edge where I've yet to install the transition. My fear is that the darkening of the tiles may not be self-correcting as they dry. The tiles were unsealed (I was planning on sealing before grouting, but didn't want to seal before laying for fear it would negatively impact the bond with the thinset) and only the ones cut by a wet saw were moistened before laying. Does the darkening mean that the tiles have absorbed the latex additive and been permanently stained from beneath, or are they just taking longer to dry than I've seen on granite counters?

I'd really hate to have to take them back up - the bond seems reallly good and the spacing/levelness I'm really happy with, so I'm hoping time will cure what ails them. How long should it take for 12"x12" porous granite tiles to dry out to their final color? These were purchased to coordinate with the vanity counter that's going in, so I'm really hoping the thinset hasn't darkened them permantly. Thoughts?

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I just had my granite guy here yesterday to once again polish and seal my bathroom granite. You can see my new post I just submitted.

I think you have to let the granite dry well and it may lighten back up.

My guy said that if you seal over a wet spot then it will stay darker.

    Bookmark   October 25, 2011 at 10:35AM
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Give it time, it can take days...a week...even longer. Depends. Example, over Ditra or another type of membrane, that can take longer than over cement board since with a membrane the moisture can only escape "up". Modified thinsets (chemical cure plus air drying) can take longer than non-modified (chemical cure) due to the air drying requirement.

Drying will usually lighten it right back up. White thinset was the wise choice. The latex modifier shouldn't be an issue, but it can sometimes effect a slight change, it really depends.

Most "splotchy" problems arise when mastic is used, those stains are indeed stains. Oil, etc.

If you intend on sealing, don't seal the granite until you're happy with the lightening. Just like bamboosmom advised. Realize that a sealer can darken it too.

If you can, also hold off on grouting. That'll give the moisture not consumed by hydration extra time to escape, for it to dry out as needed.

A lot of variables. But time will tell...

    Bookmark   October 25, 2011 at 2:01PM
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Thank you both for very encouraging and knowledgable replies - tremendously appreciated! I'll hold off on both sealing and grouting until it's dried, as suggested. I'd much rather have my timetable stretched by waiting for it to dry rather than by having to re-do! Thank you again!

    Bookmark   October 25, 2011 at 6:36PM
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This is to be expected. it'll take about 2-3 weeks to completely dry out, but it WILL dry out.

Most "splotchy" problems arise when mastic is used,

or when it's been spot set:

Difference is with thinset, the splpotchiness will pass within a couple of weeks as I said above. if it';s mastic, it'll be there for months before it disappears.

    Bookmark   October 25, 2011 at 9:37PM
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Thank you very much for the further confirmation, Bill. I'll plan on painting the walls this weekend instead of sealing and grouting, and will hold off on those until it's back to the tone of the 'pre-laid' tiles I have left over. I've got until Christmas when DD and her DH visit to get this bathroom finished, so I'll let the tile dry at it's own pace before doing anything further to it. Thank you again, I really appreciate the expert opinions!

Your and Mongo's expert advice got me successfully though 2 bathroom remods earlier this year, and I have complete faith in the advice on this final remod - want to thank you both for your wonderful FAQ's on tile and plumbing fixtures - I'd have had sooo many more problems with these bathrooms if not for the wonderful info you've both posted. Thank you both - you are a true GW treasure!

(waiting patiently for my tile to dry now....)

    Bookmark   October 25, 2011 at 11:03PM
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Glad to have been of help. Enjoy your rest while things dry out.

    Bookmark   October 26, 2011 at 1:57PM
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Yeah-- what he said. :-)

    Bookmark   October 26, 2011 at 9:19PM
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What he said --

bill and mongoct, you two guys are so terrific. I get a lot of information out of your responses, even though they're not directed at me. Keep up the good work!!

    Bookmark   October 27, 2011 at 2:23PM
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Well, while I appreciate the accolades, I have to deflect a lot of the "tile appreciation sentiment" to Bill. On GW, Bill is "the man" when it comes to all things tile.

I can answer most of the common problems we encounter here on GW, but Bill has technical and materials knowledge way beyond what I know.

One of these times when I head up to Maine I'll have to buy Bill a beer, a cup of coffee, or a bag of thinset. His choice.

Hey, coffee and donuts at Congdon's Donuts! We can get caffeinated and get a sugar high at the same time. Actually I'll pass on a donut but go for an apple fritter. Or two. Or three. lol

Best to all!

    Bookmark   October 27, 2011 at 5:59PM
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I never say no to coffee, and there's a diner right across the street. :-)

    Bookmark   October 27, 2011 at 10:13PM
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