i am relaying the block paving on my drive [it had sunk in a couple of places and some of the edges had come loose] when i took it up the sand was building not sharp so i am changing it but it was only 25mm in places is this deep enough ? and how much will it drop when i put the wacker over it?where it had sunk the most [about 1/2 m2 where the car was parked]it is about 100mm deep can i fill and wack this with sand .thanks bampi