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Discuss White grout dries brown after a few hours in the Tile Cleaning and Restoration Forum area at TilersForums.com.
Aren't these the tiles that had preformed grout lines in that were grouted in when fixed?
If so then it is possible that you could just rake out the the grout back to the tile backer and regrout.
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Reply to White grout dries brown after a few hours in the Tile Cleaning and Restoration Forum area at TilersForums.com