Abstract: A method of treating barren earthen areas for inhibiting air and sun spoilation is disclosed, the method comprising forming an aqueous slurry of calcium sulfate hemihydrate with a small amount of defoamer using a quantity of water about 25-56% above normal consistency, the hemihydrate particles having a surface area of about 4,000-16,000 square centimeters per gram; and spraying the slurry onto the barren area to form a set, substantially air-impermeable covering to the barren area that will substantially exclude outside air from the area. The method is particularly applicable to controlling burning coal spoils and inhibiting spontaneous combustion of coal refuse banks.