A flooring composition for mixing with water to produce a self-leveling slurry that quickly hydrates to form a high strength floor underlayment comprising a dry mixture of (1) beta gypsum produced by a continuous method; (2) Class C fly ash; (3) a conventional water reducing aid such as sulfonated melamines, sulfonated naphthalenes and their related formaldehyde condensates, and (4) a conventional set retarder.