EFFECT OF THE QUALITY OF GLAZE COATING ON THE FROST RESISTANCE OF FACADE TILES.

During the standard frost-resistance as well as under the actual service conditions, destruction of facade tiles starts most frequently from the glazed surface. The nature of its fracture varies, but, according to use, three main types of fracture can be identified. The first type is characterized by minute shallow cracks over the entire glaze surface in the form of crazing. The second type is distinguished by rounded cracks leading to tear-out of the material and sometimes penetrating deep into the ceramic base. The third one is represented by rounded microcracks spreading (transforming) into minute shallow splits (chips) in the glaze. The aim of the authors' investigation is to delineate the reasons for this third type of fracture. It is found that during repeated frost-defrost cycles, there is an increase in the void volume accessible to water penetration. The mass of frozen water increases leading to increased stresses. The increased stresses during repeated frost-defrost cycles lead in turn to crack formation in the glase coating. It is also shown that one of the ways of increasing the forst resistance of facade tiles is to improve the quality of glaze coatings.