Abstract: A method of producing gas concrete. Water, lime, cement and sand are pre-mixed. A calcium sulphate-containing component is subsequently mixed in and a rising agent is later admixed to form a castable mass suitable for making gas concrete by the conventional steps of pouring into a mold, permitting the mass to rise and harden sufficiently to be cut to size, and hydrothermally cured. By following the indicated procedure for making the castable mass, the calcium sulphate-containing component can be advantageously used.

Abstract: Improved building compositions are prepared by including in CaO-containing components/SiO.sub.2 -containing components admixtures a small amount of chemically precipitates silicic acid containing flourine as an impurity.A steam-cured building material preferably prepared by first pre-grinding sand with the chemically precipitated silicic acid and water, storing the resulting slurry for at least 0.5 hour and then mixing it with the CaO-containing component. The wet grinding and storing steps have been found to have a surprisingly favorable effect on the viscosity of the pumpable sand slurry and on the behavior of the risen mixture at the cutting.