The efficiency of three commercial hydrophobic coatings applied on two types of sandstones was subjected to the tests of water absorption by capillarity, water absorption by complete immersion, and frost resistance. Two days of the curing time of coatings on samples were chosen for the laboratory tests. The effects of the used coatings were different (ambiguous). Two coatings proved their effectiveness and thus, relevance of their use, but different coatings were effective on each type of sandstone. The coating F showed the best efficiency for the Hořice sandstone and coating A for the Malé Skalky sandstone. The third testing coating H was ineffective on both types of sandstone. The water absorption tests by capillarity showed a loss of the coating effectiveness over time. By completely immersing the samples in water, all three coatings lost their effectiveness and the hydrophobic effects disappeared. Applied protective coatings helped to preserve the frost resistance of the Hořice sandstone when looking at the uniaxial compressive strength after 25 freeze–thaw cycles, regardless of their fading hydrophobic effect. In addition, a penetration depth test for Hořice sandstone was performed. The impregnation depth reflects the effectiveness of the coatings and confirmed the results obtained by the water absorption tests by capillarity. The findings presented in the article are also useful in practice, as Hořice sandstone will be mined and frequently used in the future as well.

Protecting stone on facades or exterior art works from deterioration is primarily about protecting them from rainwater. Hydrophobic coatings are widely used for this purpose. Here, two factors affecting the long-term efficiency of some coatings applied on stones were investigated: the number of coating layers and the curing time after their application. Tests of water absorption by capillarity, absorption at total immersion in water, and a visual check of the penetration depth have been carried out. The coating’s efficiency coefficient C_ef was defined as the ratio of the maximum water absorption of a treated sample to an untreated one. Two commercial silicon-based coatings were applied on the highly porous Hořice sandstone alternatively. Curing times of 2 days vs. 2 weeks, and 2 coating layers vs. 3 layers were compared. The experiments showed that the coating’s efficiency is affected more by the curing time than by the number of applied coating layers. The curing time of 2 days after coating’s application is too short, but 2 weeks proved to be sufficient for both tested coatings. There was no big difference regarding the number of coating layers; two layers seem to be sufficient if a long rain-free curing time can be guaranteed.