When you lay block paving surely you have to lay it with cement rather than just sand as it hold the block down securely.
So why is this?
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A properly prepared sand base for the paving blocks provides a level surface, a support for the expected loads on the pavers and a means of allowing rain and other water run-off. The blocks are held in place by gravity and by properly preparing the perimeter of the paving area, which can be landscape timbers, concrete borders or similar.
There are liquids known as landscape binders that can be applied to the sand, but they are primarily used where slopes are involved, preventing wash-away erosion. I'm not certain if applying binder to the sand would remove the ability for rain and water seep-through, but I suspect that it would.
Concrete does not give the same visual appeal and if used as a grouting material increases the labor involved in building a paved area.