Q. Sand layer vs. cement sand used as bedding of precast concrete paving units

Cement sand is a mixture of sand and cement and it behaves as a cohesive mass once mixed. Usually a 20mm to 30mm sand layer is laid beneath precast paving block units. Though in locations of steep gradients where it stands a high possibility that rain runoff will wash out in filling sand and sand layers, cement sand should be sued instead. Correspondingly when high pressure jetting is anticipated to be used frequently in routine maintenance, sand layers beneath precast paving block units isn't preferable due to the reason of potential washing out of sand.