From the research I have done there is specialty cleaners for granite, and from what I understand you have to be careful with certain polished surfaces. I just did a web search on monument cleaning and found out very good info.
Probably the reason why it took close to an hour was I used a lot of elbow grease. I dont have a tank for my set up yet so I just hauled water in 5 gallon buckets in my truck. I am looking into getting a tank set up.