The grout in my rental hadn't been cleaned in three years and was close to black. Valley Wide Stonecare came in sprayed a solution on the tile surfaces and that's when I left. After only about an hour, they had finished. Although the grout did look cleaner, it was difficult to assess the outcome since the tile was still wet. I was assured that the grout would lighten even further as the cleaning solution dried, and it did - mostly. Overall, I was very happy with the results. Why only four stars? For one, because they use a machine, they were unable to clean the three inches of tile in the kitchen perimeter around cabinets as the machine can not reach these areas. They should have hand cleaned these areas. Otherwise they were prompt, polite and professional and would recommend.