Choosing the Right Tiles
The Definition of Porcelain
So, exactly what is porcelain tile, and is it really better than ceramic tiles? Let’s see if we can de-mystify porcelain tile.
Let’s start with this basic fact: porcelain and ceramic are not different kinds of tile. They are both ceramic tile. Porcelain is just one of many varieties of fired clay or ceramic tile. Ceramic tile, including porcelain, is made out of clay, some additives (such as feldspar, petuntse, and quartz sand), and water. Tile clay or “china clay” contains a high proportion of a mineral called kaolinite; for that reason, it is called kaolin clay or just kaolin.
How Tiles are made
The term “porcelain” has been used at least since the late 13th century to describe ceramic tile made of light-colored clay containing only a little iron oxide. To medieval Italians, the resulting tile had the color and luster of the porcellana cowrie shell. Therefore, they called it porcellana. The French corrupted the word to “porcelain” and we adopted the French word.
Tile clay is combined with other materials such as feldspar, silica, alabaster, bone ash and water into a mix called a “paste”. The paste is formed into a “biscuit” or “bisque” — the body of the tile — and heated to a very high temperature (usually between 2,000° and 2,500° Fahrenheit) in a kiln using a process that is at least 3,000 years old.
All clay tiles are fired the same way.
It is not the proportion of kaolinite in the clay that matters, but the proportion that is vitrified by firing. Firing drives out water and hardens the clay while transforming some of the molecules in the paste into a form of low-order glass. The molten glass fills up the spaces between the clay particles. The process is known as verification; once all of the spaces between the clay particles are filled, the resulting ceramic becomes essentially waterproof.
How much of the mix is vitrified depends on how long and how hot the bisque is fired.
If fired for a long time at a high temperature, more water is driven out and more vitrification occurs: resulting in a denser, harder tile more resistant to water absorption. Light-colored clays can be hard-fired, as can common red, brown or terra cotta clays. The color of the clay makes absolutely no difference to the firing process.
Tile for use in wet areas like a bathroom floor should highly slip-resistant. The tile may be hard, or not; fired for a long time, or not; and highly vitrified, or not. As used in this traditional sense, the term porcelain tells us nothing about the quality of the tile. It tells us only that the tile is made out of light-colored, porcellana clay rather than red or brown terra-cotta clay.
In the U.S., there are essentially three separate and distinct ceramics industries: ceramic tile, dishware/pottery, and sanitary ware. There is almost no overlap. Makers of fine china do not make toilets, and toilet manufacturers do not make floor tile. This is a little curious; because all three industries use basically the same raw materials and roughly the same manufacturing process; a clay paste shaped into a product — a salad bowl, sink, vase, or floor tile — and then fired at high temperature to harden the clay. Then the product covered with an impenetrable, baked-on, glass coating.
When American tile makers needed a word to describe their better-quality tile, the word “porcelain” was available and already well established in the minds of the buying public as describing ceramic products of exceptional quality. Therefore, they borrowed it, and porcelain, over time, became the term reserved for better quality American tile.
Testing & Rating Ceramic Tile
What the standards care about and do test extensively is how well the tile functions. Standards used to rate fired clay tiles are all performance standards. If a tile performs to a certain standard, it is rated for that standard no matter what it is made of; how it was made, or what color it is. Ceramic tile is subjected to a great many tests. It is tested for slipperiness, resistance to cold, heat, and chemical damage; breaking strength, wear resistance, and water absorption tests.
There are literally hundreds of thousands of tile styles, textures, finishes, and colors from which to choose. Below, we have provided a table with the most important terms and aspects that you need to understand before you purchase tiles. If you are doing the project yourself, take time to talk to the professionals at the home improvement centers and ask them for their expert advice. If you have hired a contractor, have him explain why he recommends the ones they have chosen—be comfortable with the choices and pricing before you commit.
|Group I||The softest tile – Suitable for walls and hobby crafts only, no floors.|
|Group II||Residential use in low foot traffic areas – In rooms where there is usually no through traffic, this tile might work. But, in kitchens, where there is often a lot of through traffic, this tile would be suspect|
|Group III||All residential, medium commercial, normal foot traffic (interior only) – Any bathroom or kitchen, mudroom, laundry room or hallway, but nothing outside|
|Group IV||Heavy commercial – Any interior use; suited for residential floors that get a lot of use and for exterior applications where there is not a hard freeze in winter.|
|Group V||The most wear-resistant tile – Extra heavy, high traffic, commercial (interior or exterior use)|
Choosing the Right Tiles
ANSI Rating: Resistance to Water Penetration
The rating developed by The American National Standards Institute (ANSI A137.1) is a test of resistance to permeability by water. It consists of boiling the tile in water and measuring its gain in weight from the original dry state. Four ratings resulted from their studies of clay-fired tiles. These are, from lowest to highest:
|Non-vitreous||Water absorption of more than 7.0% by volume||Tile for non-wet areas—Around fireplaces, walls, hobby and crafts use|
|Semi-vitreous||Water absorption of more than 3.0 percent, but not more than 7.0 percent||Tile for areas that may get wet on occasion, but are unlikely to see constant or standing water—Kitchen back-splashes or counter-tops, for example|
|Vitreous||Water absorption of more than 0.5 percent, but not more than 3.0 percent||Virtually any indoor application including shower walls and floors—Outdoors in areas that do not freeze—Although|
some vitreous tiles will pass the frost test, and can be used outdoors
|Impervious||Water absorption of 0.5 percent or less||Any indoor or outdoor application|