Abstract: The method for applying a heat insulation layer to an area is characterized in that alpha-hemihydrate or beta-gypsum or lime-alpha-hemihydrate or a mixture thereof is mixed as hydraulic binder with a pore former consisting of aluminum powder, mixed with ground limestone, and citric acid with addition of water and is cast in liquid or pasty form onto the area. The mixture has a pH of 11.8 or more. The constituents are preferably mixed on site, namely in such a consistency that the mixture is self-leveling. Placement on the laying site can e.g. be carried out by means of a floor screed pump. The material expands to the desired total thickness, yielding a homogeneous insulation layer of uniform thickness and quality and of high strength that will reach its high final strength after about 24 hours. The material can also be applied in a pasty consistency to a wall.