Can an impregnator be used to waterproof stone?
No. Be careful, the idea of an impregnator is to make the stone water resistant, not waterproof. In order to make the stone waterproof we would need to completely block the pores of the stone. If this is desired I would recommend a topical coating.
CAUTION If a coating is used to provide waterproofing it may cause the stone to break apart and rot. It is important that the stone be allowed to breathe, otherwise moisture can become trapped below the surface causing pressure within the stone.