An oversimplified way of defining porcelain tiles is to basically say it is a ceramic tile that has a water absorption rate of 0.5 percent or less. However, despite this sweeping statement, porcelain tiles can be separated into various types.
The characteristics of “unglazed” or “natural” porcelain tiles can be readily understood by considering the name. The tiles have not been polished, and no glaze has been applied. Natural porcelain can be full bodied, meaning that the surface and the body of the tile are the same, and the color permeates the whole piece. They can also be “double loaded”. This means that a second layer of porcelain with fine colored powered is applied and pressed together with the porcelain tile body under high pressure before it is sent off for firing.
Another variety of porcelain tile is polished. Do not be fooled by the gleam of its surface. These tiles are still unglazed or natural tiles. However the surface has been ground to a high polish with specialized material. Another misconception is that this polished surface is in fact non-porous. But the opposite is true. The process by which the porcelain tiles are polished, in fact, opens up pores on the surface. This makes the tiles susceptible to staining. To prevent this from happening, it is necessary to apply a penetrating or impregnating sealer before the installation is grouted. This sealing will also make the tiles easier to wipe clean.
Finally, glazed porcelain has had a protective glass coating applied to the surface. These tiles do not need to be sealed unless they have been polished as well as glazed. Glazed porcelain is classified as “impervious” because of its extremely low water absorption rate. This makes them a great choice for certain pools or spas. The coating also makes them resistant to damage from frost in certain exterior applications.