Recently I had the chance to demonstrate my service to an area manager for a fast food chain. He's in a store less than a year old, and the concrete is white in less traveled areas. The back dock is stained with embedded cooking oil, the drive through is oil stained. Another washer has been there twice, and could not remove this grease stain. There are short,white fiber threads coming out of the concrete. I used a heavy degreaser (1 gallon in a five gallon container), 200 degrees heat, worked on it for an hour but the result was not impressive. Can this concrete be white again?