Have used this product both on block paving and on Indian stone slabs.
Just dilute according to instructions and apply to the surface using a fine rose watering can. Some effect can be seen quite soon on stone slabs. A section of block paving which looked ‘grimy’ gradually lightened after about two months and BlockBlitz does seem to inhibit growth of weeds. A sloping, shaded concrete slab path has remained moss free practically all year. I intend using the product every six months now to save a lot of time on jet washing!