Porcelain or Ceramic: What is the difference?

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Photo courtesy Florida Tile. Tile bathroom An extraordinary tile bath. Tile used on the floor of a bath should be rated at least "Vitreous" and PEI 2 (light duty floor). The ratings are printed on the box. One of the things we are continually asked about when helping clients select flooring materials for kitchens and baths is the difference between porcelain and ceramic tile.

Here's the difference and the only difference:

     • Porcelain is a clay tile manufactured from light colored clay — white, cream, tan, gray or light brown.

     • Ceramic is a clay tile is made from a red or terracotta clay.

That's it. The only difference between the two is the composition of the clay they are made from.

Porcelain tile is not better, harder, more durable, more scratch resistant or even necessarily more expensive than ceramic tile; and if you paid more for a tile because it said "porcelain" on the box, you've just been had by a marketing trick that predates the Roman Empire. There is no generally accepted standard that distinguishes porcelain from ceramic tile for durability, longevity, clarity or water-resistance — although many manufacturers maintain their own internal standards. Tile is not "rated" porcelain, it is merely called "porcelain" by its manufacturer.

Porcelain and ceramic are both fired tiles. They start out as a clay mix, then are heated to a very high temperature in a kiln using a process at least 3,000 years old. Not every kind of clay can be used. Tile clay typically contains a high proportion of a mineral called kaolinite or "china clay". Pure kaolinite is bright white, but most natural deposits of kaolinite are red, orage or brown due to high concentrations of iron oxide Lighter concentrations result in yellow, tan or light orange deposits. Most kaolinite is red, terra-cotta or brown. Yellow and tan deposits are much rarer, and white rarest of all.

The "firing" drives out water and crystallizes some of the molecules in the clay. This makes the tiles harder and more water-resistant. How much clay is crystallized depends on how long and how hot the tile is fired. If fired hot for a long time, more water is driven out and more crystallization occurs, resulting in a denser, harder product less able to absorb water. These are the factors on which tile is actually rated. And it makes no difference whether the tile is called porcelain or ceramic. Relative hardness is important because a hard tile is less likely to wear and less likely to break. Water absorption is also important because the more water-resistant a tile, the more diverse applications it has. These distinctions do not necessarily make a tile better or worse than another, they merely determine where and how a tile may be used.

ANSI Rating: Resistance to Water Penetration

The rating developed by The American National Standards Institute (ANSI) is a test for the permeability to 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 tile. These are, from lowest to highest:

Rating Description Application
Non-vitreous Water absorption of more than 7.0% by volume. Tile for non-wet areas. Around fireplaces, for example. Typically intended for 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 backsplashes, 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.
Impervious Water absorption of 0.5 percent or less. Any indoor or outdoor application.

PEI Rating: Resistance to Wear

The second rating, developed by The Porcelain Enamel Institute (PEI), is the standard for abrasion or wear of the tile. These classifications are numeric. the numbers define the suitable uses for the tile. The higher the number, the more wear-resistant the tile.

Hard (Floor) vs. Soft (Wall) Tile

So, while we constantly hear the terms "hard" and "soft" applied to tiles by people in the building trades, the standards do not rate hardness or softness. A tile is either wear-resistant or not, and water-absorbent or not. As a practical matter however, the terms "hard" and "soft" do convey useful information. A wear-resistant tile resists wear because it is hard. A water-resistant tile does not absorb water because it is well crystallized and very dense. A hard, dense tile is made by firing the tile for a long time at a very high temperature. Softer, less-dense tile is not fired as long or at such a high temperature.

Glazing

Some fired-clay tiles, quarry tiles, for example, are not glazed, but most have a coat of the glass-like material on the face of the tile that we call glaze. Interestingly enough the glaze, which covers the wear surface of the tile, it not itself rated for wear resistance. Glass, however, is generally much more wear resistant than the tile it decorates. We have heard mentioned from time to time that the glaze on good porcelain tiles is "deeper" than that on ceramic tiles, but that's just complete nonsense. Glaze is "deep" if the producer applies a thick coat of glaze, it makes no difference what kind of backing material the glaze is applied to. This is just another of those persistent myths surrounding porcelain tile.

Where You Use It Is All That Matters

Tile kitchen cabinet Different types and sizes of tile in complementary colors make this a striking and very functional kitchen food preparation area. So in the final analysis, whether a tile is called porcelain or ceramic is not actually very important. A porcelain tile and ceramic tile with the same ratings are going to perform exactly the same way. All that actually matters is whether a tile is suitable for the application you intend.

Floor or Countertop

A tile used as flooring or on a counter top should be rated at least Group 3 for wear and semi-vitreous for water resistance. A higher rating is even better. It should also be between 3/16" and 1/4" thick, although smaller tiles and mosaics may be somewhat thinner, but not less than 1/8th inch.

Outdoors

A tile that is installed outdoors where there is a real Winter should be rated impervious to water penetration. Otherwise, water trapped within the tile may freeze, fracturing and cracking the tile. The wear standard makes little difference here since an impervious tile is almost certainly going to be rated Group 4 or 5 for wear just because it had to be fired at very high temperature for a long time to achieve the low absorption rate, and will be as a consequence be a more wear-resistant, i.e. "harder" tile.

Walls

For walls, a softer, more absorbent and thinner tile is appropriate. A rating of Group 1 is perfectly suitable for walls, but for use around water, an absorption rating of semi-vitreous or better is required. So for backsplashes, a rating of Group 2 or higher is probably safer since Group-1-rated tiles are seldom semi-vitreous.

The Final Analysis

Our best advice? Ignore the terms ceramic and porcelain when shopping for clay-fired tiles. Disregarding the artificial distinction between porcelain and ceramic tile actually makes tile choice much easier. Look for the size, pattern, glaze, price and color that works best for you in a tile rated for the application you intend. If the tile seller tries to switch you to a more expensive "porcelain" tile, look bored and yawn a lot. Now you know that there is no practical difference between the two.

End

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