Abstract <p>The paper presents the results of mechanical (tension and interlayer shear) tests of basalt plastics and the results of experimental evaluation of residual stresses depending on the appret concentration and its application technology. As the apprets, we used 3-aminopropyltriethoxysilane solutions in concentrations from 0.1 to 5%. We discover that the appret in the concentration of 0.1–1% makes it possible to increase the strength of basalt-reinforced plastics under interlayer shear up to 25%, but this has in fact no effect on its tensile strength. Increasing the appret concentration insignificantly affects the mechanical properties of basalt plastics and the rheological properties of the binder. We prove experimentally that use of the appret caused an increase of the basalt plastics’ resistance to alkali solutions, as well as to distilled and seawater.</p>