The objects of the research is plaster cement dry mixes with a modifying organomineral additive. The additive includes ground expanded clay dust as a pozzolan component and high-molecular polyethylene oxide PEO-S as a water-retaining component. The purpose of this work is to investigate the basic properties of plaster cement dry mixes with the use of a modifying organomineral additive in order to identify the effectiveness of the application of the additive. Method. Preparations of the organomineral additive were carried out by grinding the components in a laboratory planetary mill. Tests of dry plaster mixes were performed as per standard methods to GOST 33083, GOST 31357, GOST R 58277. The additive composition was optimized via the method of central composite rotatable design during of a two-factor experiments. Results. The dependences which indicate the impact of the additive components upon the compressive strength and the bonding strength to the base of dry plaster mixture-based solutions have been established. The increase in compressive strength and adhesion strength to the base of plaster mortars with an optimal content of ground expanded clay dust is explained by its high pozzolan activity; high-molecular polyethylene oxide PEO-S with a molecular weight of 4×106 provides a water-retaining effect. The dependencies that were established have served as the basis for developing dry plaster mixes which conform to regulatory requirements and are competitively viable as compared to other industrial counterparts owing to a reduction in the consumption of expensive Portland cement achieved through replacing a portion of it with ground expanded clay dust - industrial waste - and also thanks to the application of a water-retaining additive of locally produced high-molecular polyethylene oxide PEO-S instead of more expensive imported water-retaining additives.