A mortar mixture for horizontal surfaces or as casting mortar in molds has at least 20% of the mortar mixture by volume being balls composed of expanded silica sand or expanded perlite with the balls being glazed and closed at the surface thereof and filled with air. The expanded perlite balls are mixed with binding agents, additives as binders, an air-void forming agent, chemical admixtures as liquefiers, quick-setting binders, or a combination thereof, and composed of polymers. The method for producing the mortar mixture is performed by sorting perlite sand into various grain sizes by a grading curve. Each individual grain size is then expanded in a trickling channel having multi-stage temperature zones so that the surface of the balls is glazed. The glazed, expanded perlite so produced are mixed together into a homogenous mixture by adding binding agents and cellulose, air-void forming agent, chemical admixtures or a combination thereof.