HELP! Car wash that has 6 inch square tiles with 20 years of buildup

[gbattle]

Carwash interior walls cleaning

I did a test spot on a self service car wash with subway tile and white panels. I wanted to bid on it and was trying to see what it would take to clean it. I tried several products but nothing worked. I talked with the guy that was refilling the soaps and wax at the car wash, and he gave me the name of a product that worked. It was called Klean-Wall. I applied it with a pump sprayer at 4:1 and rinsed it before it dried using cold water. I purchased it at Premier Car Wash Systems in Macon,Ga. 86…