Dear Laura:
Most likely you water behind and under those tiles. Maybe it found its way through cracks in the grout. Or maybe the installer set the tiles butt-joint – whatever. You can't remove those stains, because they're coming from within the stone, not from without. Of course, matters have been enhanced by the presence of the impregnating sealer (stone in a wet environment should never be sealed), but it's too late to do anything about that at this point.
Check your grout lines and you will find the reason for the rusting of your stone.
And that is why, when somebody asks me about the suitability of certain stones for a shower enclosure, my constant answer is that the best stone is the installer that will set them in place!
May I ask you now to please read and e-sign our Statement of Purpose at:
http://www.marblecleaning.org/purpose.htm?
Ciao and good luck,
Mauri
Article ID: 1170
Created On: Sun, Feb 10, 2008 at 10:16 AM
Last Updated On: Sun, Feb 10, 2008 at 12:00 AM
Authored by: Maurizio Bertoli [mail@mbstone.com]
Online URL: https://marblecleaning.org/knowledgebase/article.php?id=1170