Going to try out this path/patio cleaner. It's currently half price instore and online and has good ratings. My previous patio cleaner Swarfega only removed a bit of surface dirt and even that I think was down to my 160 bar pressure washer.
According to the reviews it's easy to apply. Just mix in a watering can, pour over the area to be cleaned and leave for ten minutes. Then work in with brush followed by pressure washer.
Powerful cleaning non-acid fluid for exterior hard surface.