New colors of clay roof tiles became possible primarily through the use of engobe and lacquer. In both cases we receive not only an interesting colour effect, but also much smoother surface of shingle providing greater resistance to environmental factors. Initially, shade of individual items from a single batch may differ, because clays are rarely found in isotropic deposits. In addition, excessive porosity causes quick dirt accumulation, mosses and lichen germination, especially if the house is located near forest. But commonly daubing allows manufacturers to eliminate color mismatch.
Porcelain tiling – engobed or vitrified?
Clay roof tiles’ production technologies are developed in order to create a broad palette for the existing products, as well as for improvement of its technical characteristics. Engobing and glazing are contemporary methods of tile painting, based on applying respective substance (such as argillaceous liquid mass of enamel paint), so that product becomes available in various shades – brown, green, blue, black or gray.
In context of technical features, engobe significantly affects tiles’ durability against influence of various environmental factors, such as contamination, acid rains, hails and ultraviolet radiation. Terms “engobing” and “glazing” are often used as synonyms related to coloring technology. Despite similar functions and properties, there are differences to keep in mind when purchasing building tiles. They are associated, for example, with their different chemical composition. Engobe consists of specially prepared liquid argillaceous mass with admixture of corresponding minerals or metal oxides. In contrast, porcelain enamel is foremost pulverized previously melted enamel dye, enriched with inorganic additives.
Daubing does not create close texture on tile’s surface, but leaves the pores open, thus preserving good diffusive properties of roofing material. Vitrified tiling is characterized by glossy top layer, which blocks the voids. Closed structure of glazed shingles promotes that compared to daub it is characterized by even greater resistance to external agents. Smooth, almost non-porous surface of this type of tile-work substantially hinders process of dirt formation, and facilitates cleaning not only from dust and mud, but also from moss and mold.
Hue of clay shingles depends mainly on color of basic raw material. That is why mostly associated coloration for ceramic housetops is brick-red. Creation of wide tint spectrum requires, in its turn, using precious species of earthenware applied to shingles’ superficies. Engobing layer is sprayed in form of fluid mixture on dried-up shingles yet before baking in furnace. Chemical compounds are activated under the influence of high temperatures, giving workpieces colored and glance finish.
Similar process occurs in case of vitrifying, with only difference being that glazing compound partially penetrates the tile-work, creating an additional intermediate layer. Unlike engobe coating, at which coloration of finished products is based solely on thickness of applied coat, shades created with glazing are result of mineral pigments variety.
It is also necessary to remember that daubing and glaze utilization affects not only colour effect, but also responsible for item surface’s smoothness. Luster produces more homogeneous structure characterized by considerable reflection. However, if enameling ingredients are added to stoneware mixture, we obtain a precious engobe with same glitter, that porcelain enamel has, but still retaining the porous structure.