It was proposed to use synthesized calcium hydrosilicates in lime finishing dry mixes as a modifying supplement. The effect of substances containing amorphous silica, which are used in the synthesis, on the activity of the modifying supplement was established. The effect of the synthesis mode of supplement on the structure formation of lime compositions was illustrated. It was found that the injection of supplements of hydrosilicates accelerates the increase of mechanical strength. The efficiency of the using of modifying supplements of amorphous silica, such as diatomite, in the synthesis was shown. The evaluation of hydrophysical properties of coatings based on lime dry mix with the using of supplements synthesized in the presence of calcium hydrosilicates was provided. It was shown that the injection of supplements of hydrosilicates accelerates the increase of water resistance and frost resistance of coatings. It was found that the adhesion of the lime compositions with the supplement based on calcium hydrosilicates, synthesized in the presence of diatomite, is higher than that of the compositions with the addition of calcium hydrosilicates synthesized without diatomite.