This article presents scientific research on developing the optimal composition of ceramic wall materials based on local raw materials. The aim is to develop an optimal composition of a ceramic material with improved thermal insulation properties by adding a diatomite additive to the local raw materials to increase porosity and reduce density. During the research, the physicochemical properties of the raw materials, namely the clay from the Roman deposit and the diatomite from the Zhalpaq deposit, were determined. Test samples were prepared by adding 5–15% diatomite to the clay. Their physicomechanical, chemomineralogical, and structural properties were determined. For sample analysis, scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDS), equipped with a JSM-6490LV energy-dispersive microanalyzer, was used. X-ray diffraction (XRD); and Raman spectroscopy methods were used. According to the research results, adding 5-15% the addition of diatomaceous earth in the amount of 5–15% was shown to significantly affect the surface morphology, degree of porosity, structural uniformity, and agglomerate size of the studied samples, as well as the uniform distribution of elemental composition, The addition of 10% diatomite to the clay was shown to affect the change in crystalline phases and its physicomechanical properties. In conclusion, it was determined that adding 10% diatomite to the clay achieves the relatively highest degree of crystallinity, a uniform microstructure, and a relatively high compressive strength of 26.1 MPa. This showed that compared to other samples, the compressive strength increased by 15–23% and the thermal conductivity coefficient decreased by 1–11%. Thus, adding 10% diatomaceous earth to the clay was found to be an effective modifier.