Porcelain tile has a water absorption rate of 0.5 percent or lower as defined by the American Society for Testing and Materials (ASTM) section C373. To test this, the fired tile is first weighed, then it is boiled for five hours and left to sit in water for 24 hours. Then it is weighed again. If the tile weighs less than half of one-percent more as a result of water-absorbing into its surface, it is considered impervious porcelain. To achieve this density, a special kaolin clay mixture is used, which is finer and purer than most ceramic clay. It usually contains notable levels of quartz and feldspar mixed in. Porcelain tiles are fired at temperatures ranging from 2,200 to 2,500 degrees Fahrenheit. To the consumer, it generally suffices to say that porcelain is a dense, fine-grained, smooth tile that is impervious to water than ordinary ceramic tile. Porcelain tile typically receives a surface glazing treatmentâ??a coating of liquified glass materialâ??while some forms of ceramic tile are left unglazed. As a rule porcelain tile is more impervious than ceramic tile and is thus subject to less water infiltration.
