# Porcelain Enamel Coatings for Building Facades
## 1 Introduction  
One of the main issues in the sector of facade engineering is the selection of materials able to guarantee long-term structural durability [1]. Within the realm of architecture, the primary role of cladding is undeniably to shield the building from environmental elements, yet its significance extends beyond mere protection. Indeed, the exterior coating also shapes the building's visual impression, a crucial factor given that buildings influence the value of their surrounding urban landscape. Hence, aside from representing a protective barrier, architectural cladding must present pleasing hues that harmonize with the external surroundings, along with aesthetic qualities. Moreover, it should possess the flexibility to accommodate diverse architectural structures, enabling architects to explore varied design strategies. Changes in the exterior appearance of buildings are an obvious consequence of natural exposure, with a negative impact both on their functional and aesthetic properties. In addition to the construction costs, a large economic outly is thus needed to preserve the building exterior, and a large fraction of all the money invested in the construction sector is spent on maintenance [2, 3]. The goal is thus to exploit durable materials resistant to aggressive conditions to extend the service life of buildings, reducing the need for intervention for maintenance. Another aspect to consider for materials selection in the architectural field is the ease of cleaning. Indeed, a significant fraction of the total maintenance costs is attributed to the removal of soiling caused by environmental pollutants and contaminants [4] and graffiti [5, 6]. Ultimately, panels designed for the exterior of buildings should meet two specific requirements. First, they should prove long-term durability and resistance, withstandpotentially damaging environmental conditions, and be easily cleanable. Secondly, they ought to exhibit favorable aesthetic qualities, as the visual appeal of a structure is significant and should not be overlooked. Currently, the predominant materials employed for the realization of building facades are coil coatings, painted panels and components, anodized aluminum, and stainless steel. While these materials offer viable solutions, they also possess inherent drawbacks and limitations. Coil coatings and painted panels are largely applied in the architectural sector, mainly thanks to the low cost of construction. These coatings may, however, undergo degradation after UV exposure, which is dependent on their composition [7]. The resistance of coil coatings was found to be reduced after natural exposure, as well as after the accelerated laboratory salt spray test [8]. Furthermore, to maintain low usage costs and facilitate the bending of components, the protective thickness of coil coatings must remain relatively low. The construction of facades made of stainless steel, including colored stainless steel, is cost-effective in the long run and allows combining the brightness of the surface with high resistance to corrosion and to aggressive conditions, such as acid rain [9; 10]. Some issues are, however, related to the heavy weight of this material, which may be mitigated by the use of composite materials [11]. Moreover, anodized aluminum finds application in facade engineering, mainly for its long-term durability and the protection from corrosion conferred by the oxide layer. It has been recently shown that the anti-corrosive properties of anodized aluminum remain intact even when the material is mechanically deformed [12]. However, there is an increasing demand for a wide range of color options, and this represents a limitation for the use of anodized aluminum, which is generally available only in a limited color palette. Among the organic coatings, paints are the most commonly used for the cladding of buildings. Self-cleaning paints with a superhydrophobic surface are available and employed to prevent the excessive accumulation of air pollutants and dust [13].