An analysis of the main types of basic building mixtures for 3D printing and the requirements for their basic properties is presented. Using the mathematical planning of experiments, a complex of polynomial models of the properties of cement-ash fine-grained concrete mixtures for 3D printing was obtained. These properties included their “open time” extrusion suitability, the structural strength required for layering the mixture after a certain time after mixing, tensile strength during splitting characterizing the adhesion of layers and the compressive strength of extruded concrete. As mineral admixtures, the concrete included fly ash and the hardening accelerator: building gypsum. A laboratory printer was designed and used for the research. On the basis of the obtained models, an analysis of the factors of the composition of cement-ash concrete mixtures for the investigated properties is carried out. The article shows a solution to the optimization problem according to the criterion of the minimum cost of the composition of a fine-grained concrete mixture for 3D printing using computer software.