# Factors Affecting the Efficiency of Hydrophobic Coatings--Experience from Application on Sandstone
## 3 Results
### Results of the Water Absorption Tests
#### 3.2.2 Efficiency of the Funcosil SNL  
Saturation profiles without and with the Funcosil SNL coating are presented in Figure 8. Raw data from the tests are again in Table S1. The samples from the series 2x/2d reached WAC = 8030 g\(\cdot\)m\({}^{-2}\) within 48 h and from that moment they behaved like the untreated ones. This shows that the impregnation effect disappeared within 1 day only when the curing time was too short. Sample series 2x/2w and 3x/2w yielded quite similar saturation profiles. Certain increases in saturation rates after 8 h indicate partial loss of the hydrophobic effect. However, at the end of the tests (30 days), WAC equals only 8600 g\(\cdot\)m\({}^{-2}\). This is a value that was already noticed in untreated samples after 2 days. Comparing these two sample sets, coatings with 2 weeks of curing brought a decrease of 20% of the WAC found in untreated samples. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Sample Series** & **Sample** & **m\({}_{1}\) (g)** & **m\({}_{2}\) (g)** & **m\({}_{3}\) (g)** & **m\({}_{3}\)–m\({}_{1}\)** & **Mean** \\ \hline \multirow{4}{*}{2x/2w} & H-17 & 234.45 & 235.02 & 234.76 & 0.31 & \\ \cline{2-6}  & H-18 & 236.40 & 236.93 & 236.64 & 0.24 & \\ \cline{2-6}  & H-19 & 236.33 & 236.77 & 236.44 & 0.11 & \\ \cline{2-6}  & H-20 & 239.30 & 239.88 & 239.57 & 0.27 & \\ \hline \multirow{4}{*}{3x/2w} & H-29 & 238.41 & 238.98 & 238.67 & 0.26 & \\ \cline{2-6}  & H-30 & 239.45 & 239.99 & 239.68 & 0.23 & \\ \cline{2-6}  & H-31 & 242.36 & 242.92 & 242.55 & 0.19 & \\ \cline{2-6}  & H-32 & 236.86 & 237.42 & 237.07 & 0.21 & \\ \hline \hline \end{tabular} \(\text{m}_{1}\)—initial dry mass of untreated sample, \(\text{m}_{2}\)—mass of sample with Antipluviol S after 2 weeks of curing, \(\text{m}_{3}\)—dry mass of sample with Antipluviol S after all water absorption tests.  
\end{table} 
Table 4: The mean dry mass of the coating remaining in the samples after all water absorption tests—Antipluviol S. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Parameter** & \multicolumn{5}{c}{**Samples**} \\ \cline{2-6}  & & **Untreated** & **2x/2d** & **2x/2w** & **3x/2w** \\ \hline \multirow{4}{*}{Water absorption by capillarity \(N_{WAC}\) (\%)} & average & 11.48 & 8.32 & 1.10 & 1.17 \\ \cline{2-6}  & max & 11.92 & 8.54 & 1.60 & 1.51 \\ \cline{2-6}  & min & 11.17 & 8.16 & 0.83 & 0.79 \\ \hline Efficiency coefficient \(C_{\mathit{effWAC}}\) (-) & & - & 0.73 & 0.10 & 0.10 \\ \hline \multirow{4}{*}{Water absorption by complete immersion \(N_{WAI}\) (\%)} & average & 12.16 & 9.57 & 2.63 & 2.74 \\ \cline{2-6}  & max & 12.71 & 9.77 & 3.44 & 2.97 \\ \cline{2-6}  & min & 11.83 & 9.31 & 2.33 & 2.23 \\ \hline Efficiency coefficient \(C_{\mathit{effWAI}}\) (-) & & - & 0.79 & 0.22 & 0.23 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Efficiency parameters of Antipluviol S.  
Results of \(N_{WAC}\) are compared to \(N_{WAI}\) in Table 5. Funcosil SNL totally lost its protective effect when cured only for 2 days; those samples finally reached similar values of N\({}_{WAI}\) to the untreated sandstone (the small absorption increase is within the accuracy limits of the method). However, this coating type seems to be less effective than Antipluviol S after 2 weeks of curing time, as fully immersed samples contained a higher amount of water. Already the capillary absorption was much higher, which is visible when comparing Figures 7 and 8. The efficiency of 20% that was reached after 2 weeks of Funcosil SNL curing and observed in the test of water absorption by capillarity disappeared after 30 days under water; the hydrophobic effect was lost and N\({}_{WAI}\) of fully saturated samples became close to that of untreated samples. The dry masses of both series, 2x/2w and 2x/3w, are also the same or even lower than before treatment. All of this indicates that Funcosil SNL was significantly dissolved and washed out when fully immersed in water for 30 days (Table 6). Figure 8: WAC curves—samples with Funcosil SNL coatings compared to untreated ones.