What is Porcelain Tile and what are the different kinds of porcelain tiles?
According to the the Tile Council for North America, porcelain tile is defined as an impervious tile with a water absorption of 0.5% or less as measured by the ASTM C373 test method.
What are the differences between porcelain tiles and non-porcelain tiles?
Porcelain tiles are typically made with "porcelain" clays that have specific properties. Typically, these tiles are dense and by definitio, they have water absorption of 0.5% or less. Non-porcelain tiles have water absorption greater than 0.5%.
Because porcelain tiles have a low water absorption, they are usually frost resistant, although, not always. To know if a tile is frost resistant, you should check the manufacturer's literature.
There are also many non-porcelain tiles that can be used in freeze thaw environments and that are manufactured with properties similar to porcelain tiles.
There are both glazed and unglazed porcelain tiles. It is important to know the difference, as the glazed variety is usually a little easier to clean. Typically, glazed porcelain tiles have filled in microscopic holes that could be present in the unglazed tile. On the other hand, unglazed porcelains may have better slip resistance.
Non-porcelain tiles cover a wide range of properties. Typically they are glazed (unglazed quarry tile is the exception), and the glaze layer can be extremely durable. However, as there are differences from one glaze to another, it is important to check if the tile has been tested and to make sure the glaze hardness is suitable for your application.
In general, non-porcelain tiles are easier to bond to the floor and usually easier to cut. Porcelain tiles are harder to bond and harder to cut. While this can be relevant to the tile installer, it generally makes little difference to the end-user, so long as the installer uses the right materials.
Some people refer to unglazed porcelain tile as "through body" ( i.e., the color on the top goes all the way through). Even in extreme applications, these tiles tend not to show wear as the porcelain is quite durable (harder than granite), and the color goes all the way through.
Many glazed porcelains also have extremely good durability. Although the color in the glaze layer may be different from the body, the surface is usually sufficiently resistant to abrasion to not show wear in typical applications.
Since 1999, U.S. and European manufacturers have been using the same testing method for determining glaze wear resistance - with a value of 4 (on a scale from 0 to 5) being good for almost all applications except the most abrasive and dirty environments. However, lower ratings are also fine depending on where the tile will be used and how much traffic and outside dirt (especially sand, because it is abrasive) will be present.
A rating of 4 can be achieved if there is no visible wear (under test conditions) after 2100, 6000, or 12000 revolutions of the test equipment. A value of 3 can be achieved by passing 750 or 1500 revolutions. Usually the product specifications will indicate which value was passed when the testing was done (for example, one tile might be rated Class 3, passing 1500 revolutions, another tile could be Class 3, passing only 750 revolutions).