The invention relates to a mortar mixture which can be embodied as insulating plaster, in the form of a plastering mixture, for insulating building envelopes, and which can also be embodied as final coat. However, the mortar mixture can be used for horizontal surfaces or as casting mortar in molds, including pressing molds. At least 20% of the mortar mixture by volume consists of balls composed of expanded silica sand or expanded perlite, which balls are glazed and thus closed at the surface thereof and are filled with air. Said perlite balls are mixed with binding agents, additives as binders, an air-void forming agent, and/or further chemical admixtures as liquefiers, quick-setting binders, and composed of polymers. The method for producing the mortar mixture is performed in such a way that perlite sand is first sorted into various grain sizes by means of a grading curve. Each individual grain size is then expanded in a trickling channel having multi-stage temperature zones such that the surface of the balls is glazed. Glazed, expanded perlite produced in such a way is mixed together into a homogenous mixture by adding binding agents and cellulose, air-void forming agent, and/or chemical admixtures. The mortar mixture is used to insulate exterior or interior walls or floors of buildings. For this purpose, the mortar mixture is sprayed through a hose (7) and through a nozzle (10), with or without the addition of water, onto a wall to be insulated, by means of a screw pump having a screw (1) and having a pump cylinder (3), to which pump cylinder air pressure or oil pressure can be applied from outside in the region of the screw (1) and which pump cylinder is housed in a pressure-resistant outer pipe (4). In the use of the mortar mixture as a final coat, an aqueous dispersion is used as binding agent.