Recently we completed a challenging project refinishing the stone floor of a large hotel lobby and dining area. The stone was not marble – it was a slate that was smooth on the surface, unlike some of the rough texture slate tiles.
The main problem was that the grout lines had not been installed correctly, so the grout color was inconsistent. In order to fix the situation, a previous contractor had done a colorsealing job on the grout lines, but it had not covered the grout uniformly. So the grout had a patchy, inconsistent look. NOT what you want in the main lobby of a hotel!
This is a close up of the grout they didn’t like and the overall look in a corner: