## 3 Results
### Characterizations of the Coatings Applied on Raw Lecce stone
The curves of the amount of water capillary absorbed by the samples per unit area Qi (kg/m\({}^{2}\)) at time ti plotted as a function of the square root of time (in seconds) are shown in Figure 5. The data are averaged on five samples for each type of coating. The slope of the linear fit to the curve in Figure 5 in the first 60 min gives the absorption coefficient AC\({}_{60}\), reported in Table 3. No significant differences in the absorption behavior are observed in the coated samples. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Oxide** & **Uncoated (wt\%)** & **TP-Hy/N-TiA** & **TP-Hy/P25** \\  & **(wt\%)** & **(wt\%)** & **(wt\%)** \\ \hline SiO\({}_{2}\) & 4.41 & 28.56 & 31.68 \\ P\({}_{2}\)O\({}_{5}\) & 3.17 & b.d.l. & b.d.l. \\ CaO & 89.78 & 62.76 & 46.17 \\ TiO\({}_{2}\) & b.d.l. & 7.83 & 21.60 \\ FeO & 2.64 & 0.85 & 0.54 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Semi-quantitative composition of uncoated and coated _Lece stone_ samples obtained by EDS analysis on the areas of Figure 4. wt% = concentration of the oxide; b.d.l. = below detection limit. Figure 5: Capillarity water absorption tests carried out on _Lece stone_ before and after treatments: (**a**) uncoated and TP-Hy/N-TiA; (**b**) uncoated and TP-Hy/P25. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Lece stone** & \(L^{\star}\) & \(a^{\star}\) & \(b^{\star}\) & \(\Delta E^{\star}\) \\ \hline Uncoated & 80.9 (5) & 1.5 (4) & 14.3 (7) & - \\ Coated TP-Hy/N-TiA & 79.9 (8) & 2.1 (4) & 15.3 (9) & 1.5 (9) \\ \hline Uncoated & 82.3 (6) & 1.8 (3) & 14.6 (5) & - \\ Coated TP-Hy/P25 & 80.6 (3) & 2.5 (5) & 16.7 (4) & 2.8 (6) \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Colorimetric data of coated and uncoated _Lece stones_. In brackets is the standard deviation. As expected, the untreated _Lecce stone_, being characterized by high porosity, absorbs large amounts of water: in the first ten minutes, it reaches approximately half of the total absorbed water and continues to absorb water for the entire duration of the test (five days) without reaching a constant value. On the contrary, the two treatments show high effectiveness in reducing water absorption by capillarity. At the end of the test, the Q\({}_{\text{I}}\) values of the coated samples are approximately 50% lower than those of the untreated stones. _Lecce stone_ is characterized by high permeability to water vapor. The results of the reduction of vapor permeability on coated samples are reported as the variation in the mass of water vapor through the stone as a function of time measured at the steady state. Steady state was reached in 96 h for both treated and untreated samples. The two coatings show similar behavior: the reduction in vapor permeability is significant, about 40%, for both treatments. It is not unusual that hydrophobic coatings can result in a strong reduction in water permeability when used on porous substrates [16; 93]. Static contact angle (CA) measurements were carried out on uncoated and TP-Hy/N-TiA- and TP-Hy/P25-coated samples. On uncoated _Lecce stone_, due to its large porosity, the drop is immediately absorbed, making it impossible to measure the CA. On the contrary, the surface of the treated samples shows a high water-repellency, as evident from the photos of the water drops shown in Figure 6.  
Water repellence is a desirable property of the surface to reduce water-induced degradation in natural stone. Therefore, several studies are aimed at giving stone surfaces greater hydrophobicity (120\({}^{\circ}\) \(<\) CA \(<\) 150\({}^{\circ}\)) [30; 31; 32; 49; 93] or, even better, super-hydrophobicity (CA \(>\) 150\({}^{\circ}\)) [53; 85; 94]. Hydrophobic treatment is clearly very efficient in the protection of the stone by water. Both treatments show very high CA values, suggesting super hydrophobicity: for TP-Hy/N-TiA, CA = 150 \(\pm\) 3\({}^{\circ}\), and it is slightly lower in the case of the TP-Hy/P25 treatment (CA = 147 \(\pm\) 5\({}^{\circ}\)).