Foamed concrete or mortar contains up to 80% by volume of void space, with densities as low as 300 kg/m3 and 28-day strengths of between 0.2 and 20 MPa. It is typically produced by blending cement, fine sand or fly ash and water into a preformed foam or by mechanically foaming the appropriate mix using a foaming surfactant. For the low densities below 600 kg/m3, no fillers are included but for densities up to 1600 kg/m3, limestone dust and concreting sand may be incorporated. Foamed concrete is free flowing, may be pumped and requires no compaction. When set, the material offers good frost resistance and thermal insulation. It is therefore used for trench reinstatement, filling cellars or to provide insulation under floors or in flat roofs.