Ceramic tile is a clay based, semi vitreous, product with a fired glass surface. The clay is either red or white bodied.
 
 As a general rule the red body clay is used for floor tile as it is stronger than the white body clay, which is used almost exclusively for wall tile.

 The glass surface varies in hardness and is rated by PEI codes 1 through 4+.
 PEI 1 is wall only,
 PEI 2 is for walls and residential bathroom floors only,
 PEI 3 is residential floors 
 PEI 4 and above is rated for commercial floors.

 The absorbancy of clay tile is usually too high to be considered frost proof and would normally be used in interior applications only. Outdoor use can and will result in damage to you Tile.

Grades of Ceramic and Porcelain Tile.
 
 There are three grades of fired tile, standard (STD or Class 1), Seconds (STDII or class 2) and builders grade (unclassed).

 Standard grade tile has met all the size, finish, color and dimension requirements and will have defective rating of 3% or less.


 Seconds grade tile are tile that have been culled out of standard grade runs due to variations in size, finish, color or dimensions.


 Builders grade tile is uninspected and will usually have more than the standard 3% defects.