Development of waterproof engobe layer for ceramic wall tiles

Ceramic wall tiles, which are the most popular wall coverings, are especially used for internal applications due to their high porosity and high water absorption. When the tile body absorbs water after laying, water mark problem, which is a common phenomenon in ceramic tiles, occurs. The aim of this study was to increase the current understanding about how the engobe characteristics (opacity, fusibility, permeability) and the type of frit used in engobe compositions influence the water mark formation of a wall tile body. For this purpose, mainly three different types of engobe compositions were developed by using diopside-based, zircon-based, and titanium-based frits. The sintering behaviors of frits and engobes were characterized by using a heating microscope. Water permeability features were measured by water drop test and ink test. The structural and morphological characteristics of the engobes were investigated. This study revealed that increasing engobe fusibility prevents the water mark formation. However, reducing the engobe porosity alone is not enough to solve the problem; the engobe composition should have sufficient opacity. Type and amount of the frit in engobe formulations determine the melting behavior, opacity, and permeability feature of the engobe layer. According to the results, the engobe composition with desired opacity and permeability could not be achieved by using diopside frit due to its melting behavior and dissolution of diopside crystals. On the other hand, engobe compositions using zircon-based and titanium-based frits contributed to minimizing the water mark problem with the formation of zircon and titanite crystals and their impermeable structures.