Why is my New Marble Floor Tile Discoloring?


Hello- We are in the middle of a bathroom remodel in our home. The tile I selected for the floor is either a grey marble or limestone (2" hexagon). The bathroom is on the 2nd floor of our house and the tile installer used Ditra over the subfloor. He used Schluter All set for the setting material for the tile. The tile was installed on 9/15/20. Since installation there has been much discoloration in many tiles. We have reached out to many people in the industry and the consensus is that it is moisture. There has been some improvement since 9/16/20 but there is still a lot of discoloration in the tile. I live in Arkansas and am looking for some expert help to problem shoot and resolve this issue. Do you all provide consulting for this type of problem? The feedback I have heard is that it could take up to 45 days to see if the moisture will dissipate if it is going to dissipate. I am trying to find out additional information to see if this is indeed a moisture problem. If so was the correct setting material used for the tile installation. If it is moisture how long does it take to dissipate and correct and is there a chance that it will not correct? We ran short on tile and had to order more. I told the installer to wait to install to make sure we can get this resolved. If we are able to get it resolved is there a setting material that should be used to finish the installation? I do have pictures that I can send. Any help or a referral to someone who can help us would be greatly appreciated. Thank you so much!


ANSWER - The marble may in fact be retaining moisture and maybe it will go away after it dries out.  On the other hand natural stone has various minerals within it that can react with moisture and leave stains that may or may not be removable.

Considering the marble is installed over the Ditra mat that is impervious so moisture can't be pulled away from the wet Schluter thin-set mortar adhesive and the marble is impervious so it can only absorb very little of the moisture in the thin-set mortar adhesive.  So depending on how thick the Schluter adhesive was applied it will take longer for it to cure/dry the thicker it was applied.  The Schluter All Set is an ANSI A118.15 polymer modified mortar so it will even take longer to dry because of the water retaining polymers it contains.  It is unlikely that the All Set is causing a problem in terms of some stain from it is migrating into the marble.

So without doing an expensive forensic investigation, your best bet is to see if it will diminish over time.  You put a fan in the room to help the moisture in the thin-set to evaporate.  If the stains don't go away you can try using a poultice to pull the stains out.  If the stains were caused by something from the surface of the marble you might be able to grind and refinish the surface to remove them.  If the stains are caused by minerals within the marble they might not be removable. If that is the case you can try using an enhancer sealer that might even out the coloring so the discoloration isn't obvious.

2 thoughts on “Why is my New Marble Floor Tile Discoloring?

  1. Keryn Fishman says:

    Hi! I just had 12×24 ombra grey marble tiles installed for a shower. They used a cement material that has made circle stains on the marble. It’s been 3 weeks with fans and the stains are lightening but not gone. Is there a chance they are still drying or is this a lost cause? Once they do dry to my liking should I seal and grout or grout and then seal?
    Very upset!!

    • Donato Pompo says:

      Marble is very dense. Per ASTM C503 a true marble cannot have more than 0.2% absorption that makes it impervious. So it should absorb very little moisture.

      To have circle stains makes me think that the marble may have been etched by the cementitious material or some other acidic material. If that is the case it will not go away. Although you can repolish the marble and that should remove it.

      Although marble is very dense and low absorbing it is worth while to seal it to help prevent any kind of etching or staining as long as the condition causing those stains are removed right away. Sealers do not last that long so every 6 months or so you might need to reapply if water doesn’t bead up on the surface.

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