Understanding Materials: Ceramic Tile
Ceramic products are varied and depending on their manufacturing processes, they exhibit their own special qualities and properties. The hardness of the ceramic material is directly attributed to its manufacturing process, and generally references the Mohs Scale to categorize its hardness.
The Manufacturing Process
Ceramic tile production begins with the excavation of clays to be used in the manufacturing process. Depending on the type of tile being produced, any number of two to six different types and colors of clay may be necessary to blend together in a mixture.
The selected bulk clays are mixed with water and this mixture is pumped into large, rotating cylindrical mills, where extreme grinding action pulverizes the clay into uniform and homogeneous particles. This substrate is called body-slip, and has the consistency of a milk shake.
Next, moisture from the body-slip is evaporated by a spray dryer burner, creating fine particles of uniformly sized dry clay called powder. The powder is then fed into molds within a hydraulic press, where it is molded under pressure (approximately 4,000 PSI) to form green ware (what the tile is called prior to being fired). The green ware is dried again to further reduce the moisture content, and then travels down glaze lines where various types of glazes are applied to the surface.
The glazed green ware travels through a kiln and undergoes a 45-50 minute firing where temperatures can reach 2300°F causing the glaze to fuse to the body. The tile that emerges from this process is very hard, durable and impact resistant.
Hardness of Ceramic Tiles
- Water absorption rate, glazes, compression and material all determine the hardness of ceramic tile
- The percentage of water absorption by the tile body determines whether the ceramic tile is Impervious, Vitreous, Semi-Vitreous, or Non-Vitreous. From Impervious, where absorption rates of 15% and higher, hardness factors change
- Most glazes fall in the 5 to 6 Mohs Scale range. However, certain types of floor and porcelain tiles can have compressive strengths of 10,000 PSI and a Mohs hardness factor of 8