Non-typical defects on surfaces of ceramic and roof tiles: Nature and the causes

Abstract

This research was conducted to identify the nature and the cause of non-typical defects which appeared on the visible surfaces of ceramic and roof tiles. Microstructural analysis was conducted via optical microscope and scanning electron microscope coupled with energy dispersive spectrometer. Ceramic tiles contained black spots and dark brown clusters with yellow halos. Black spots originated from carbon contained in starting glaze raw materials. EDS analysis of clusters of dark-brown color in the pores showed the presence of Fe, which is found to affect the quality of the visible tile surface. Non-homogeneities on the roof tiles surfaces appeared in the form of stains and manifested after immersions in water or aspersing water on the tile surface. The cause of inhomogeneities was a local phenomenon due to the porous structure of micro cracks caused by coarse metallic grains that are imported with the raw materials.