The material for the bedding layer should be coarse concrete sand. Do not use stone dust or screenings; they do not allow the pavers to “seat” properly and do not allow for drainage. The sand should be an even 1″ thick layer. Do not compact the sand setting bed. Do not mix portland cement into the sand used for the setting bed or the joints between pavers. It defeats the flexibility of the system, and it cannot be cleaned off the surface of the pavers.