I have tried all type of cleaning techniques to get my concrete driveway clean. The problem I am having is that I had a company put down a sealant on my driveway after thoroughly power washed and it must not have been a good product. It left several parts of my driveway rather blotchy and stained looking. That was about 3 years ago and now this summer it still looks blotchy, but, I believe alot of the old sealant is gone. These are just old stains that I want to get up. What is the safest and most effective technique to use to get the driveway clean like new again and then what is a good sealant to put on the driveway therafter?