Cleaning Monoblock?

[Bammer]

Hi.It has been a long time since I sought some advice but I am sure that the answer is here-as always. I usually use a karcher p/washer to clean my monoblock drive but wondered if there is a pre treatment that can acclerate the process prior to using the p/washer? I generally use sodium chlorate for the moss/weeds in between the blocks but would welcome advice as how to do a good job of the cleaning and also the type of sand to backfill with after using the p/washer. Many thanks. TC