It's been almost a year since I power washed the concrete so today was the day. The dirt and mildew gets down deep in the concrete so it's more than a quick rinse to get it off. You have to hold it down close and do about a two inch strip at a time. Bottom line is that it took all afternoon to do the front drive. The back is great since I put the concrete coating down a few months ago. It only takes a quick rinse to get it clean.