I just had a new tiled walk-in shower installed by a local contractor with antique white grout. The tile was set on thinset with a Denshield tile backer. We applied Stone Tech Professional Heavy Duty Impregnator-Pro grout sealer a couple of days after grouting and allowed about two days for the sealer to dry. After using the shower for a couple of days, there were several places (on the floor and towards the bottom of the walls) where the grout turned a mopwater gray color. We did not use the shower for two weeks and most of the original color returned. I guess it dryed out. We then reapplied the sealer. After a day or two of using the shower (5 or 6 times) the discoloration is back and seems to be getting worse.
Can anybody tell me what is going on here and what can I do to stop it?