Light Weight Flooring Concrete FL400 How to use First, clean the surface to remove loose particles or anything that may reduce adhesion. Then, splash some water onto the surface. Prepare the concrete by mixing the powder and water based on the suggested ratio. Add the powder to the water gradually to reach the desired consistency. Use a trowel to apply the concrete. The constructed floor is ready to use after at least seven days. The minimum thickness of applied concrete is 5 millimeters. This product can be used to construct thick layers. Since this product benefits from LECA aggregates, the heat of hydration, which is one of the problems of mass concrete, will not occur. Proper curing is required to get maximum strength and durability.