# Porcelain Enamel Coatings for Building Facades
## 2 Materials and Methods
### Characterization  
The thickness of the coating was measured using a Phynix Surfix FN thickness gauge (Phynix, Neuss, Germany). The roughness of the surface was measured through the MAHR Marsurf PS1 roughness tester (Mahr, Gottingen, Germany), with an evaluation length of 5.6 mm and a sampling length of 0.8 mm, according to the ISO 21920-2 standard [26]. Five measurements were conducted to find the surface average roughness values. The surface and a cross-section of enamel samples were observed at the scanning electron microscope SEM JEOL IT300 (JEOL, Akishima, Tokyo, Japan). Various accelerated tests were carried out, carefully selected to replicate the harsh conditions that building facades could potentially face. In fact, facades should ensure protection during a long service life, during which they can be worn and damaged due to environmental and atmospheric conditions. In this context, conventional assessments for gauging material deterioration were employed. Furthermore, adhesion tests were executed, as a robust adhesion between the metal substrate and the coating is pivotal in ensuring the elevated level of protection provided by the coating layer. Lastly, the capacity to resist abrasion was tested, given that this represents a conceivable form of mechanical damage that building claddings might encounter. The adhesion between the coatings and the substrate was evaluated through a direct impact test, following the ASTM B916 standard [27]. Despite this standard being the reference for the evaluation of the adherence of the porcelain enamel coatings to metals, the same parameters were also used to evaluate the adherence of the paints to the metallic substrate, so that there could be a direct comparison. Accordingly, after conditioning the samples at a temperature of (23 \(\pm\) 2) \({}^{\circ}\)C with a humidity of (50 \(\pm\) 5)% for 16 h in the Angelantoni climatic chamber DM340 C (Angelantoni DM340 C, Angelantoni Test Technologies, Perugia, Italy), a 1 kg weight was impacted on the sample surface with an energy of 9.03 J.  
Durability tests specific to enamel coatings are often lacking. Thus, the tests conducted in this study are inspired by a series of standards generally used to study the durability of paints. Given the probable coating-concrete contact in the architectural sector, the resistance of enamel coatings to the chemical attack by concrete products was investigated considering the EN 12206-1 standard [28]. Three spots of mortar (15 g Ca(OH)\({}_{2}\), 41 g of concrete, and 244 g of sand with water) were applied to the sample surfaces. The samples were maintained for 24 h at a temperature of (38 \(\pm\) 3) \({}^{\circ}\)C and humidity of (95 \(\pm\) 5)% in an Erichsen Hygrotherm 519 SA humidostatic chamber (Erichsen, Hemer, Germany). The mortar was removed, and surfaces were cleaned with water. Eventually, variations in the aesthetic properties were evaluated through the gloss and color change measurements. The gloss was measured with a Glossmeter Erichsen NL34 (Erichsen, Milan, Italy), for an angle of 60\({}^{\circ}\)[29], taking 5 measurements per spot, while color measurements were performed with the Konica Minolta CM-2600d spectrophotometer (Konica Minolta, Tokyo, Japan), with a D65/10\({}^{\circ}\) illuminator/observer, according to the CIELab color space method [30]. The entire procedure was repeated three times. The reported values of gloss and color changes are the average values of the three measurements for each sample. To evaluate the resistance to corrosion of the coated metals and to highlight eventual problems of loss of adhesion, samples were continuously exposed to the salt spray chamber (Ascott Analytical Equipment, Tamworth, UK) with a 5 wt.% NaCl solution at 35 \({}^{\circ}\)C, following the procedure of the ASTM B117 standard [31]. At the test endpoint, delamination around the scribe was evaluated as per UNI EN ISO 4628-8 [32]. The test was conducted on two samples per typology.