Sand play in children's play areas - RoSPA
Sand depth should be at least 450mm and 75-150mm from the top. The top edge should be smooth and suitable for sitting on (by parents) or for building on. The base should be a gravel base (100-150mm) draining to a field drain, a 20-25mm of charcoal (if available) or geotextile material (i.e. Terram 1000 grade) and an open weave of bricks 10mm apart.