Ceramic and Porcelain Tile Information Resources

Ceramic tiles are constructed from a few basic ingredients that are blended together into what is referred to as clay or a bisque.  This is usually a mixture of natural sediments like gypsum, talc, shale, and sand.  This mixture is blended together with water to create the resulting clay.  The clay is then pressed into a mold of the shape and size desired.  After the tile hardens it is fired in a kiln.  This process hardens the tile further.  How long and at what temperatures will depend on what purpose the tile is being produced for.

Ceramic tile comes in many different finishes. Most are glazed using a thin layer of glass over the clay tile surface. Other types of ceramic tiles are not glazed or are un-glazed. These tiles have a more natural earthy appeal.  Un-glazed tile usually have a matted look like natural clay. Tile color will be determined by either the clay used or colored mineral that are added.

The processes by which tiles are created determine the intended uses for that type of tile. There are two processes for creating tiles. One is called monocottura or single fired. The other is called bicottura or double fired. A single fired tile has the clay and the glazed baked at the same time. A double fired tile has the clay baked first. Then the glazed is applied and the tile is baked again.

Not only is the single fire process a time saver but it also creates a stronger more durable tile. Tiles that are fired twice or more times are generally used on walls. Backsplashes are a good example of a common use for double fired tiles. Otherwise indoor used only is recommended with low foot traffic due to the softer nature of these types of ceramic tiles.

Un-glazed tiles are very good for outside tile installations. Stain resistant, low moisture absorption rates, frost proof, fire proof, and slip resistant. These characteristics make un-glazed ceramic tile very durable.

About Ceramic Tiles

To help you in deciding whether or not that tile you just love is right for you ... there is a system of measurement that defines the durability called the PEI or PE rating. This comes from the Porcelain Enamel Institute. Basically all ceramic tiles are placed into groups according to strength and so the suggested usage. The greatest emphasis of the measurement is on foot traffic. Basically the PEI tests the resistance to wear and scratch. The Ratings goes from one to five. One being the lowest strength and five being the highest strength. Below is a chart that indicates what the suggested usage is for each strength number 1 - 5.

PEI Rating Guide Chart

PEI 1 Very Light Traffic
Tiles should be used on interior applications only. For use in areas like kitchen countertops and backsplashes.  Can be used in very light foot traffic residential floors.
Not recommended for areas that will have any type of frequent or heavy foot traffic.
PEI 2Light Traffic
These types of tiles should be used for interior walls, interior countertops, light foot traffic residential interior floors.
Not recommended for use in rooms like kitchens, stairs, doorways, entryways, or areas with any type of frequent or heavy foot traffic.
PEI 3Moderate Traffic
This type of tile should be used on interior walls, interior countertop, residential interior floors.
Not recommended for commercial use.
PEI 4Moderate to Heavy Traffic
This type of tile should be used on interior walls, interior countertop, residential interior floors. and light commercial projects.
This tile should not be used for heavy commercial projects.
PEI 5 Heavy Traffic
This type of tile should be used on interior walls, interior countertop, residential interior floors. and light commercial projects. This tile is good for Industrial projects where durability is necessary. 


Shade/Color Variations Industry Standard Codes Chart:

(V1) Uniform Appearance:
Basically little to no difference among pieces from the same production batch. Ceramic tile are manufactured using the same finish applications.
 (V2) Slight Variations:
Barely noticeable differences in color ranges or patterns within similar colors.
(V3) Moderate Variations:
Notable differences in color ranges or patterns within similar colors.
 (V4) Dramatic or Random Variations:
Extreme color variation, one tile may have totally different colors and look very different from that of the other tiles.  Clients should look at many different pieces of tile to get a good idea of the and color and or pattern variation involved. This type of tile should be laid out and sorted before installation proceeds in order to ensure what the final look will be.

Rectified Tiles:

Rectified tile is tile that has been finished mechanically on all sides to consistent dimensions.  An extra step is included in the production of rectified tiles to grind them down to precision cut sizes. Usually the most sought after benefit of rectified tile is that the uniform tile sizes allows for extra narrow grout lines.  The narrow grout lines create a more seamless look. In order to really achieve a seamless look grout lines for rectified tiles should be at the very least 1/8 wide in order to benefit from the seamless appeal.

Non-Rectified Tiles or Calibrated Tiles

Non-rectified tiles are known more by the name calibrated tiles.  The majority of all tiles sold is of this type.  They are different than rectified tiles in that the dimensions for each individual tile will vary slightly.   The biggest differences stem from different production runs of the same tile.  No extra procedures are taken to ensure consistent dimensions.   Depending on the size differences between tiles ... wider grout lines are needed for uniformity of the grout lines during the installation process.

Porcelain Tiles:

This type of tile is usually constructed by a pressed method of porcelain clays.. The result is a tile which is much denser than ceramic, impervious, fine grained with a smooth surface face. Porcelain tiles have a much lower water absorption rate (less than 0.5%) than non-porcelain. This quality improves durability and makes porcelain tiles frost resistant. Glazed porcelain tiles are even harder and can tolerate much more wear and tear. Porcelain tiles are suitable for any application from light traffic to the heaviest residential and light commercial traffic.

Full body porcelain tiles carry the color and pattern through the entire thickness of the tile making them virtually impervious to wear. Full body porcelain tiles are suitable for residential to the highest traffic commercial or industrial projects. Porcelain tiles are available in a matte, unglazed, and a high polished finish.


The information contained in this document represents the current view of Duval Tile & Stone on the issues discussed as of the date of publication.

This White Paper is for informational purposes only.

Duval Tile & Stone, http://duvaltileandstone.com/ MAKE NO WARRANTIES, EXPRESS OR IMPLIED, IN THIS DOCUMENT.