Nicolas has a time proven method for drive cleaning. After clearing away any obvious debris from the site, he applies a treatment to loosen the lichen's grip on the block surface, then uses a high pressured turbo lance, inch by inch to get that lichen off and the worst of the moss. After that comes a surface cleaner directs high pressure jets straight down deep cleaning every crack and crevice. When everything looks spotless, it isn't as there are bound to be the black spots of Aspergillis mould which can range from a few dots to large black areas under trees. Nicolas gets rid of them too.
It's not over yet. You get a sparkling clean and usable drive. After a couple of days to dry, Nicolas will turn up again to re-sand it. This isn't just a cosmetic thing. He uses a special kiln dried sand. Powdered engineering which holds those blocks together to counter subsidence.