There are three types of sub base most popularly used for block paving - consolidated reclaimed crushed concrete, MOT Type 1 crushed stone and lean-mix concrete. Having completed many drives over the past 20 years, we always use a lean mix concrete base of 100-125mm for a driveway. We have this delivered on site semi dry, rake to levels and consolidate with a vibrating plate. The bedding sand is then spread, consolidated with the plate to a depth of approx. 50mm and screeded to the required levels, allowing the blocks to sit no more than 6mm proud of the finished job. A pass with the wacker will settle the blocks to the required level. Sweep in top sand with a final pass of the waker and job done. In all that time, we have never had a drive rut or sink as so often happens with the other two methods.