# Porcelain Enamel Coatings for Building Facades
## 3 Results and Discussion
### Damage Induced by Human Activities  
In addition to the deterioration due to service exposure, building exteriors are often damaged by human activities. The application of graffiti on building facades is a common practice with very severe consequences. Indeed, in addition to the costly procedures for cleaning, building exterior surfaces may also be irreversibly damaged [45]. The use of a material able to resist both graffiti and aggressive solvents used for graffiti and surface cleaning would thus be an advantage for the building designers. Figure 8 presents the results of the graffiti resistance test, specifically focusing on the variation in gloss and color parameters. The enamel coatings showed excellent resistance against graffiti and the aggressive solvents used for cleaning (MEK and xylene), maintaining unchanged gloss and color parameters. On the other side, the paint coatings suffered during this accelerated test. Indeed, after two cycles of graffiti application and removal, the paint detached from the substrate due to the interaction of polymeric matter with the organic solvents. The removal of the graffiti spray from painted surfaces proved to be challenging, either with MEK or with xylene solvents. Instead, already after just a few passes of the solvent-soaked cotton on the enamel surface, the graffiti spray easily detached, facilitated by solvent uptake, without causing damage to the appearance of the samples. The use of xylene appeared to be more aggressive on the red paint than the use of MEK, as in the former case a steep gloss reduction was observed already after the first use  
Figure 8: Variation in (**a**,**b**) gloss and (**c**,**d**) color during the graffiti resistance test using MEK and xylene solvents. of the solvent (Figure 8a,b). Conversely, the white paint seems to be more sensitive to the MEK solvent. These results highlight the superior performance of enamels in cases of contact with graffiti and aggressive organic solvents, which makes them a more favorable option for designers of building cladding. Abrasion is one of the most frequent mechanical damages that enamel coatings must withstand. In an outdoor environment, abrasion is frequently induced by the action of wind; small particles of dust and sand carried by the wind may indeed damage surfaces due to long-term rubbing. Additionally, cleaning procedures also contribute to surface abrasion damage. Different studies have proved that the composition of the frit influences the abrasion resistance of enamels [46; 47]. In this work, the abrasion resistance of the porcelain enamel coatings under study was evaluated through two abrasion tests, i.e., the Taber and the PEI tests, as they are employed for the study of the abrasion resistance of paints and enamels, respectively. The Taber and the PEI abrasion tests imply different abrasive processes, and they provide different information on the resistance of the coating. The two-body abrasion Taber test is generally used to investigate how abrasion mechanisms influence the aesthetic properties of organic coatings [48; 49]. Abrasive particles present in the abrasive grinders induce sub-superficial damage with the formation of cracks on the coating surface. In the Taber test, debris accumulates in the areas of the enamel coatings that are comparatively weaker, specifically where sub-surface pores exist. This debris has the tendency to infiltrate the porosity to some extent while also contributing to surface abrasion through sliding wear by positioning itself between the grinding wheels and the substrate. The damage induced by the alumina together with the steel balls during the PEI test is instead more uniform, also thanks to the presence of water acting as a lubricant [46]. In the latter case, the damage is more uniform, with no formation of cracks. By comparing the mass loss during the Taber abrasion test (Figure 9) and the PEI abrasion test (Figure 10), it is evident that paints suffer more during the Taber test, while enamels suffer more during the PEI test.