# Factors Affecting the Efficiency of Hydrophobic Coatings--Experience from Application on Sandstone
## 5 Conclusions  
Two types of hydrophobic coatings, Antipluviol S and Funcosil SNL, were applied on the highly porous Horice sandstone to test the impact of both the coating's curing time and the number of applied coating layers. Two and three layers were compared. The coating medium penetrated deeper with three layers, but without any significant effect upon the efficiency of the coating compared to two layers. The curing time of 2 days turned out to be insufficient for both coating types. The curing time of 2 weeks was long enough, leading to ca. 90% reduction of the water absorption by capillarity with Antipluviol S. It represents a good protection against water absorption. Reduction of this parameter with Funcosil SNL reached only 20%. Notably, the test of water absorption by capillarity proved to be suitable for a fast first check of the coatings' efficiency. Two days of this test is sufficient for that purpose; it is not necessary to perform longer testing. Though the water content absorbed by capillarity constantly increased (with rates <1% per day) for the next 28 days in all stone samples, the non-resistance of the protective coating could be recognized after 48 h in water.  
The higher efficiency of Antipluviol S was also confirmed by the underwater saturation over 30 days. The coating cured for 2 weeks remained in the treated sandstone even after such a long leaching time. This can be seen on the higher dry masses of those samples (series 2x/2w and 3x/2w) compared to the initial dry masses, i.e., before the application of Antipluviol S. Identical treatment and testing of samples with Funcosil SNL showed the loss of the already limited protective effect after 30 days of full immersion in water. The total water absorption was not reduced, nor was any dry mass increase observed when compared to untreated samples. Despite 2 weeks of curing, the Funcosil SNL coating must have been dissolved and leached out. This makes its application in humid climates with frequent heavy rains questionable. Resources in the Podhorni Ujezd quarry guarantee future production and application of the popular Horice sandstone as building and decorative stone. Therefore, findings presented in the paper are directly applicable in practice.  
The following supporting information can be downloaded at: [[https://www.mdpi.com/article/10.3390/app14114541/s1](https://www.mdpi.com/article/10.3390/app14114541/s1)]([https://www.mdpi.com/article/10.3390/app14114541/s1](https://www.mdpi.com/article/10.3390/app14114541/s1)), Table S1: Raw data.  
**Author Contributions:** Conceptualization: T.D. and L.D.; methodology: L.D., R.A. and T.D.; formal analysis: R.A.; investigation: L.D. and T.D.; writing--original draft preparation: L.D., T.D. and R.A.; writing--review and editing: R.A.; visualization: L.D. and R.A. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This research was partly financed from the project VEGA1/0182/23 granted by the Scientific Granting Agency of the Ministry of Education, Research, Development and Youth of the Slovak Republic, and was supported by the Comenius University in Bratislava through the Grant for Young Scientists UK/28/2022.  
**Institutional Review Board Statement:** Not applicable.  
**Informed Consent Statement:** Not applicable.  
**Data Availability Statement:** The original contributions presented in the study are included in the article and Supplementary Material; further inquiries can be directed to the corresponding author.  
**Conflicts of Interest:** The authors declare no conflicts of interest.