Got my veralgten flagstones first cleaned on the sidewalk with scrubbing brush and water, let it dry and then sprayed with MEM-stone impregnation. Since then, the plates remain clean, it put no more algae-resistant and water runs off - as it is described on the container. That's why I decided to treat my patio slabs so. It has incidentally proved to be very inconvenient to handle the plates with a pressure washer: You Serden superficially rough, it is made up of dust in the pores from the algae and provides the best support. Therefore, one should his plates rather not deal with the pressure washer, except spraying them afterwards immediately after drying with stone impregnation. Then rest.
