What would you guys do in this situation. We were cleaning a job in a commercial building and all the areas come perfectly clean and we were using grout master Robert Allen. When we got to the last room I did it like I did all the rest and I couldn't get anything to clean this grout. The tile came clean as you can see to the right of the picture but grout was unchanged no matter what I used. I had a trailer full of my go to products nothing would phase it. Any suggestions?