We had 3" octagonal Alabama white honed marble tiles installed as a kitchen backsplash on August 1,2007. About two hours after the installer finished grouting the tile, the tiles began to turn varying shades of grey. They are still grey two months later and the veining appears as dark smears instead of veining. The installer did use white Versabond thin set and the tile was installed over newly installed dry wall. The tiles have not been sealed to date.
Can anyone tell me what happened and what we need to do?