A hydraulically setting mortar composition containing at least one hydraulically setting component, at least one lightweight filler, at least one cellulose ether, at least one setting retarder and optionally further additional additives, particularly fillers and/or dispersion powders. In addition, a premix for producing a hydraulically setting mortar composition is described containing at least one lightweight filler and at least one cellulose ether and/or a setting retarder. As a result of the inventive ratio of these components, it is possible with much lower lightweight filler contents to obtain more cost effective mortar formulations and/or improved use characteristics, such as e.g. increased adhesive tensile strengths and/or an increased open time. The hydraulically setting mortar composition can be used in gypsum, gypsum-lime, lime-cement, cement and/or thermal plasters, tile adhesives, masonry mortars, full heat protection mortars, surfacers, self-levelling floor materials or repair mortars.