I have seen this before and it is possible it is iron or some other mineral. One way to find out is to use a product from Alpha called RSR2000. This works great as a reagent. place a small amount on the stone and if it turns purple you have iron. Getting rid of it is another problem. A grout release may help but you may have a problem with the grout adhereing to the stone. One solution is to use an epoxy grout or you can try a grout with pure latex additive with no water.

On Mon, Dec 28, 2009 at 8:37 PM, Roger Konarski <qm144@yahoo.com> wrote:

All,
Would appreciate input on what’s causing this problem. Please see attached picture. This floor were just installed and grouted. The problem is the red stains on the edge of the tiles. What is causing the problem? My thoughts are that the moisture from the grout is oxidizing minerals in the stone. If that is the case, would applying a sealer before grout stop this from happening? They have already laid 600 sq.ft. of the tile, any suggestions on removing the red spots? I my thoughts is to try to see if it is iron that is oxidizing and taking the appropriate steps. Or trying poultice with a hydrogen peroxide.
Thanks in advance for your help.
Roger Konarski

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