# Porcelain Enamel Coatings for Building Facades
## 3 Results and Discussion
### Accelerated Weather Tests
The enamel coatings showed good adhesion with the substrate, as no delamination was observed. Differently, complete delamination was obtained for the painted samples, pointing out a complete absence of adhesion between the coating and the substrate. Enamels offer effective protection against the contact of Cl\({}^{-}\) ions and aggressive solutions with the substrate due to their non-permeable characteristics and the strong adhesion with the substrate generated through chemical reactions during the firing process. Conversely, the higher permeability of paints, as well as the lower adhesion strength, allow the Cl\({}^{-}\) ions to penetrate more easily and reach the substrate. The good adhesion of enamels  
Figure 4: Variation of (**a**) gloss and (**b**) color during test of resistance to concrete products. during the salt spray test seems to be in contrast with the impact test results, during which a weak adhesion was reported for the red enamel. Nonetheless, this is explained by the fact that the loss of adhesion during the impact test involves mechanical aspects, while the loss of adhesion during the salt spray exposure is linked to chemical degradation. Continuous exposure to solar radiation may alter the aesthetic properties of a surface. To investigate the resistance of enamel coatings to solar radiation, panels were exposed for 1000 h to UV-B radiation, and changes in surface properties were evaluated through color and gloss change measurements. Both the white and the red enamel coatings showed stable gloss values upon exposure to UV radiation. Differently, the paints experienced a significant reduction in gloss (Figure 6a). Furthermore, the paints displayed significant color changes following exposure in the UV chamber, with color change \(\Delta\)E values exceeding 3 points (Figure 6b). The color change in the white paint primarily manifested as a shift towards more positive b* values, while the red paint exhibited a reduction of b* and a* parameters. If the white porcelain enamel shows extremely high color stability, the red one is more susceptible to UV-B exposure, with \(\Delta\)E close to 1. This color variation in the red coating was primarily attributed to a decrease in the a* color parameter, indicative of a shift towards the green spectrum. Figure 5: Enameled (**a**) and painted (**b**) samples after the salt spray test. In fact, Se-based pigments tend to undergo photochemical reactions when exposed to UV radiation, which can result in color variation. Air pollution poses a major threat to the preservation of architectural structures. Different studies agree on the fact that air contaminants and pollutants significantly contribute to the degradation of buildings [41; 42; 43; 44]. Thus, an ideal coating for panels of buildings should resist dust and pollutants present in the service environments. To assess the effects of weathering and soiling on enamel coatings, the procedures outlined in the ASTM D7897 standard [34] were followed. This involved the fouling of samples with a solution that mimics the presence of salts, particulate organic matter (POM), powders, and soot present in the service environment. After each cycle of weathering--soiling--weathering, color, and gloss measurements were performed to evaluate changes in the aesthetic of the surface. A significant gloss variation was observed for paints but not for enamel coatings (Figure 7a). Moreover, in this case, the white enamel demonstrated higher color stability than the red enamel (Figure 7b). The latter indeed shows \(\Delta\)E values higher than 1 already after one soiling cycle, with a shift of a* and b* toward more positive values and a decrease in the L* parameter. Due to their instability and reactivity, red pigments may have reacted with chemicals present in the soiling solution, exacerbating their degradation under the influence of UV radiation. Figure 6: Variation of (**a**) gloss and (**b**) color during the exposure to UV-B radiation. Figure 7: Variation in (**a**) gloss and (**b**) color during the soiling and weathering test.