Porcelain Tile vs Ceramic Tile: What Is the Difference?

One of the things we are fre­quently asked about when helping clients select flooring and countertop materials for kitchens and baths is the dif­ference be­tween porce­lain and cera­mic tile.
People have a sense that ceramic and porcelain tiles are different, and that porcelain tile is somehow the better of the two, but they're not sure why it is better. 1
So, exactly what is porcelain tile, and is it really better than ceramic tile? Let's see if we can de-mystify porcelain tile.

The Euro­pean Def­ini­tion of Por­ce­lain
Let's start with this simple, basic fact: porcelain and ceramic are not different kinds of tile. They are both ceramic tile.

Ceramic is a word derived from the ancient Greek "keramos" meaning roughly "of fired clay". 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.

But, not just any old backyard clay will do. Tile clay or "china clay" contains a high proportion of a mineral called kaolinite, and, for that reason is called kaolin clay or just kaolin. Kaolin results from the chemical decay of silica minerals, mostly feldspar. Pure kaolin is bright white, but white deposits are very rare. Most natural deposits of kaolin also contain iron oxide which darkens its color. A little oxide results in yellow, tan, pink or light orange clay. A little more iron oxide produces the more familiar red or brown terra-cotta clay. It takes very little iron to color kaolin. Typically iron content is below 3% in even the reddest of China clays.

The term "porcelain" has been used at least since the late 13th century 2 to describe ceramic tile made of light-colored clay containing only a little, if any, iron oxide. To medieval Italians, or so the story goes, the resulting tile had the the color and luster of the much admired shell of the porcellana cowrie. So, that's what they called it: porcellana. The French corrupted the word to "porcelain" and we adopted (the French say "purloined") 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 at least 3,000 years old.

All clay tile is fired the same way. Folk wisdom has it that porcelain clay makes a better tile because it contains a higher proportion of kaolinite than red or terra-cotta clay. But, that's nonsense. There is not enough iron in terra-cotta clay to have any significant effect on the firing process. The plain truth is that it is not so much 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 vit­ri­fi­ca­tion3 — which is just a fancy name for turn­ing some­thing into glass. If 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 more common red, brown or terra-cotta clays. The color of the clay makes absolutely no difference to the firing process.

So, our first definition of porcelain — the traditional or European definition — is a tile made from light-colored clay.

It is the color of the clay that defines porcelain for the traditionalists. 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 a red or brown terra-cotta clay.

The American Definition of Porcelain

The Firing Process

A bisque is fired in four stages. The temperature of the kiln is slowly increased until the desired firing temperature is reached, then the tile is slowly cooled until it reaches room temperature. The higher the target firing temperature and the longer the bisque is held at that temperature the harder and more water resistant the resulting tile.

Stage 1. Drying: (up to 480° F). Re­si­dual wa­ter re­moved. Tem­pera­ture is raised slow­ly to pre­vent ex­plo­sive va­pori­za­tion.

Stage 2: De­hy­drox­y­la­tion & Ox­i­da­tion: (480° to 930° F) Chemi­cally bonded or "lat­tice" water eva­por­at­ed (de­hy­drox­y­la­tion), or­gan­ic mat­ter burns off (oxi­da­tion).

Stage 3: Vitrification: (930° to 2,700° F) Kaolinite particles crystalize through several intermediate states as the temperature rises, finally trans­forming into mullite and cristobalite; glassy components of the bisque melt and flow into the spaces between the clay particles.

Stage 4: Cooling: (2,700° to room temperature) Tile is allowed to return to room temperature slowly to prevent cracking.
The traditional American definition of porcelain is very different — almost the exact opposite, in fact. It derives from the particular American experience with fired clay products.

In the U.S. there are essentially three separate and distinct ceramics industries: ceramic tile, dishware/pottery, and sanitaryware. 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 is 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 is covered with an impenetrable, baked on, glass coating.

In the early days, American tile manufacturers rarely made traditional porcelain tile. If someone wanted porcelain tile, he got it from Europe. But, the other clay industries adopted European porcelain very quickly, and their products soon earned a reputation for being of exceptional quality. By 1917 Lenox had replaced various European companies as the purveyor of fine china to the White House. American Standard had firmly established the "American standard" for nearly faultless porcelain bathroom fixtures by the turn of the 20th century.

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. So, they borrowed it, and porcelain, over time, became the term reserved for better quality American tile.

There is some evidence that American porcelain tile followed the European practice of using only light-colored clay for a few years. But, over time this limitation began to give way so that by the 1970s the term was applied to any high-quality tile no matter the color of the clay. Today, American porcelain may have a tile body that is red, tan, white, brown — any color so long as the tile is of good quality.

So, in the American tradition, the defining characteristic of porcelain tile is the quality of the tile, not its color. The tile may be of any color — color does not matter — but it must be a tile that is considered by its manufacturer to be a high quality product.

Full-Bodied and Through-Bodied Tile
The problem with the American definition is that it conflicts with the general public perception of porcelain. While most people don't know much about porcelain, they do know that it is a light-bodied tile, not red or brown. Consequently, tile sellers often meet with a lot of skepticism when they try to sell terra-cotta tiles as porcelain.

To overcome this problem, American tile manufacturers have come up with a clever distinction between red or brown and light bodied porcelain tile. Light-bodied tile is "full-bodied" or "through-bodied" porcelain. So, the salesman can tell you, with an absolutely straight face, that the wine red terra-cotta tile you are looking at is actually porcelain, it's just not "full-bodied" porcelain — implying that you must be an unwashed country hick for not knowing the difference.

Silly Porcelain Myths

A number of myths have grown up around porcelain, most of them utter nonsense. Here are a few of our favorites.

Porcelain glaze has a depth and luster not available on ordinary ceramic tile. The truth is that glaze is deep and lustrous if the manufacture applies a thick coat of lustrous glaze. It makes no difference what it is applied to. Glaze can be applied to clay tile, steel, iron, pottery, china, even concrete — in fact, just about any material that can stand the firing temperature. The notion that porcelain glaze is somehow deeper and more lustrous is just plain nonsense.

Porcelain tile is made from a special "refined" porcelain clay. Horse patootee! Of course, each manufacturer has its own "secret formula" for tile, but there is no universally recognized special clay mixture used to make porcelain tile. But, this fact has not slowed the many "composition" myths surrounding porcelain tile. These suggest that the clay formula used in porcelain has some special or unique properties. We have seen statements that porcelain contains "at least 50% feldspar", or is made of pure kaolinite "cleansed of all impurities", or consists of a "special sand-like substance" (a "sand-like substance", when heated in a kiln produces glass, not tile).

Here are some of our favorite variations on the composition myth found just recently on the web from folks who should know better:
“The only difference between Porcelain tile and regular ceramic tile is that the clay used in porcelain tile is more highly refined and purified. Consequently, porcelain tiles are denser than a standard ceramic tile.” “Porcelain tile is a tile that is generally made … from porcelain clays which result in a tile that is dense, impervious, fine grained and smooth, with a sharply formed face.” “Porcelain tiles are composed of fine porcelain clays and fired at much higher temperatures than ceramic tiles.”
It's all total balderdash, there is no special clay formula for porcelain tile.

Porcelain tile is harder to install than ceramic tile. Any well fired, dense, hard clay tile is more difficult to install than softer tiles not fired as long. Hard tiles are less porous and may, but do not always, require a special setting adhesive to bond well to whatever surface they are being installed on. They are also denser and harder to cut with diamond saws. These characteristics apply to any hard fired ceramic tile. Nor does porcelain require any "special tools" to install as suggested by some "experts"(See e.g. FastFloors.com. All the tools required are in any tile setter's tool box.

Irreconcilable Differences

So, we now have two almost opposite and conflicting definitions of porcelain:
So, if the tile store clerk claims that the tile you are looking at is "porcelain", what does he mean? Is it a high quality tile, or a light bodied tile? Both? When you buy a tile labeled "porcelain", just what are you buying?

Testing & Rating Ceramic Tile

Although some tile "experts" expound at length on the "special" and "unique" properties of the clay mix used to make American porcelain tile, there is, in fact, no such special clay mix (See sidebar). There are absolutely no composition standards at all for general-use clay tile. No one cares about the type or color of the clay used or just how much or how little kaolinite, or feldspar, or quartz sand, etc. is included in the mixture. Manufacturers can make tile out of any composition and color of clay, and include any additive that they think will produce a better tile. The standards don't care one way or another.

Nor does anyone particularly care about the process used to make the tile. Any manufacturing process that will work is just fine. The tile can be shaped by machine, or by hand; by using huge high-pressure presses, or as an extrusion, or by globbing the clay paste into a form. The tile can be fired using the old tunnel kiln, or the newer roller-kilns, or a kiln at the local high school. With rare exception (for special purpose tiles — the heat-shield tiles on the space shuttle, for example), the standards simply don't pay attention to how a tile is made.

What the standards do 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 gets rated for that standard no matter what it is made of, how it was made, or what color it is.

Ceramic Tile Performance Standards

Tile is subjected to a great many tests. It is tested for slipperiness, resistance to cold, heat, and chemical damage, breaking strength, and stain resistance, among others — and we will touch on a few more of these tests later in this article. But, the two most widely used — and certainly the most widely quoted and misquoted — tests of fired clay tile are the wear resistance and water absorption tests.

The wear resistance test, developed by the Porcelain Enamel Institute (PEI) reveals how well the tile resists damage from foot traffic. The absorption test, supervised by the American National Standards Instituted (ANSI), looks at how waterproof a tile is.

These distinctions do not necessarily make one tile better or worse than another, they merely help determine where and how a tile may be used. A tile that absorbs a lot of water should not be used outside where it freezes because the freeze-thaw cycle will crack the tile. But, it may be quite suitable as wall tile around a fireplace where water absorption matters little. A tile that is not very hard may not be suitable for floors or counter tops, but will be just fine for walls, backsplashes, and hobby crafts where surface wear is not an issue.

PEI Rating: Resistance to Surface Wear
The rating developed by The Porcelain Enamel Institute, is a test of surface wear resistance. It involves applying steel ball bearings and aluminum oxide (the grit used in sandpaper) to a tile. A tile is scored by how quickly it shows visible signs of wear.

The classification is colloquially known as the PEI Scale or "Wear Scale". The classifications are numeric. The numbers define the suitable uses for the tile. The higher the number, the more wear-resistant the tile and the more places it can be used. Rectified Tile
When the guy at the tile store tells you that the tile you are looking at is more expensive because it has been rectified, it sounds vaguely ominous — like someone's been naughty and sent to the principal's office. Just what does he mean?

Tile that is fired at very high temperature loses most of its moisture, causing the raw tile bisque to shrink. Shrinkage is very controlled these days so that the finished size or "caliber" of the resulting tiles is very uniform — usually less than 1/16th of an inch difference from tile to tile. But, if the tile has to all be exactly the same size, it is "rectified" by cutting all the tiles to exactly the same size on a saw or grinder. This extra step adds a little to the price of the tile

Rectified tile is for special applications and is just not needed for most home uses, so don't pay for it unless your tile installer insists you actually need it.

GroupPermissible Application
Group IThe softest tile. Suitable for walls and hobby crafts only, no floors.
Group IIResidential 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 IIIAll 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 VThe most wear-resistant tile. Extra heavy, high traffic, commercial (interior or exterior use).

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:

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 or countertops, 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. The frost test is discussed later in this article.)
Impervious Water absorption of 0.5 percent or less. Any indoor or outdoor application.

As we explained earlier, "vitreous" just means "glass-like". So, don't get waylaid by the fancy name. A vitreous tile is less porous than a semi-vitreous tile because more of the tiny spaces between clay particles have been filled with glass. A semi-vitreous tile is less porous than a non-vitreous tile.

An impervious tile is the least porous — in fact, it is essentially waterproof — but instead of calling it super-vitreous or waterproof, the creators of the test settled on "impervious". It's not really impervious in the common meaning of the English word. Hit it with a hammer, it will shatter. Sounds impressive though — like it will stand up to almost any abuse. It won't.

There is a relation between the two ratings, at least for unglazed tile such as quarry or saltillo tiles. Tile that is harder and thus more wear resistant is tile that was fired longer or at a higher temperature, or both. This is also the tile that tends to be more resistant to water penetration. With glazed tiles, however, the relationship breaks down. If a tile has a surface glaze, the glaze becomes the wear layer, and it is the glaze that is subjected to the PEI wear test, not the body of the tile beneath the glaze. A very hard glaze can be applied to a very soft tile body, so, with glazed tiles it is possible to achieve a high wear rating with a low water-resistance score. More about tile glaze below.

The ANSI Definition of Porcelain Tile

We already have two different definitions of porcelain tile: the traditional or European definition, and the newer American definition. And, just to make things even more fun, there is yet a third generally accepted definition: the ANSI definition of porcelain.

Under pressure from American tile manufacturers and seeking to clarify once and for all time the burning issue of what is a porcelain tile, the American National Standards Institute in 1988 adopted what it hoped would become the only official U.S. definition of porcelain tile in ANSI A137.1 which declared a tile to be porcelain only if it is:
"…generally made by the dust-pressed method of a composition resulting in a tile that is dense, impervious, fine-grained, and smooth with sharply formed face."
While this is definitely written in engineer-speak, what it does is define two different tests for identifying a porcelain tile. The first is the same performance test used to rate all tile. A porcelain tile must perform at the highest, "impervious", standard in the ANSI water-absorption test (See above). The second is something rarer — a "process" test. To be called porcelain, tile must be made by the "dust press" method or process.

What is the dust or "dry" press method? It's a process for manu­fac­turing tile that has very lit­tle to do with tile quality. It is mostly a measure for con­trol­ling tile shrink­age.

In 2007 the Tile Council of North America and the Ceramic Tile Distributors Association formed a joint venture called the Porcelain Tile Certification Agency (PTCA) to test and certify ceramic tile as meeting the American National Standard Institute's (ANSI) definition for porcelain tile.

To be considered porcelain under the ANSI definition, the tile must score as “impervious” on the ANSI water absorption test (see above). If the tile passes this test, it is given a certificate indicating that it is “porcelain” under the ANSI definition of porcelain.

The certification mark may be used on the tile's packaging and marketing materials to show that the tile is considered porcelain as defined by ANSI. So, if you see this mark on the tile box you may be sure that the tile is water-resistant enough to be used in any indoor or outdoor application. Of course, if all you are tiling is a shower wall or a backsplash, this is much more durability than you actually need, so why pay more for it? See “How to Actually Buy Tile”, below.
All fired clay tile shrinks when it is fired and water in the biscuit evaporates. If there is a lot of water, there is a lot of shrinkage. Controlling shrinkage is important if the resulting tiles are to be the same finished size, or "caliber". Caliber is important. If tiles vary too much in face dimensions they are much harder to set in a pleasing, uniform manner and often require a wide grout line to mask the unevenness of the tile. Tiles that are very similar in finished size can bet set more easily with a narrower grout line.

The dust press method uses very little water to dampen the clay mix which is then pressed into shape in a machine press. The high pressure helps the clay particle stick together so the bisque retains its shape. With so little water in the mix, shrinkage is minimal and the resulting tiles are likely to be of a more uniform size.

The other, more widely used method, is the extrusion process in which slightly wetter clay is fed into a mold that extrudes a ribbon of biscuit that is then sliced into individual tiles. In the past, shrinkage was a little less controlled using this method.

However, since 1988 tile chemists and engineers have made enormous strides in controlling shrinkage using the extrusion process — primarily by reducing the amount of water needed in the paste — so much so that extrusion now produces very uniform tile. Recognizing this change ANSI dropped the requirement that porcelain be made by the dust press process in its later versions of A137.1. Any manufacturing process can now be used to make porcelain tile as long as the tile rates "impervious".

The effect is that "porcelain" under the ANSI standard has become just an alternate name for an "impervious" tile. If a tile meets the criteria for being rated "impervious" to water penetration, it may be called porcelain.

American tile manufacturers welcomed the new standard with warm applause and great enthusiasm. European, South American and most Asian tile makers greeted it with a great big yawn, and cheerfully ignored it.

Imported tile is generally rated under a different set of standards published by the International Standards Organization (ISO), which had until recently, very wisely, stayed out of the fray over what is or is not porcelain tile. Consequently, imported tiles generally adhered to the European tradition — tile is porcelain if it is made with light-colored clay and its manufacturer elects to call it porcelain.

The ISO Definition of Porcelain Tile
But, not having an "official" definition of porcelain caused problems for the ISO. The U.S. market for ceramic tile is huge, about equal to the entire continent of Europe, so most foreign tile manufacturers want to export to the U.S. But, in order to get an official porcelain designation for their qualifying tile, they needed to be certified by ANSI. This started costing ISO customers as more manufactures shifted to ANSI for tile certification. So, in 2012 the ISO finally caved in. The ISO 13006:2012 standard that defines and classifies ceramic tile announced a definition of porcelain tile, adopting with minor variations the same definition as ANSI — a tile may be called porcelain if it absorbs less than .05% water by volume, or is, in other words, rated "impervious" in the ANSI water absorption test. (Actually, the ISO has its own slightly different test — why let the ANSI guys have all the glory, right?)

So, finally, everyone is on the same page and there is a universal definition of porcelain that every tile maker has to observe. Right?

Not a chance! Sorry! Wish it were that easy.

If ceramic tile was required to be rated by law, then a standard defining porcelain would eliminate any issue about what is or is not porcelain tile. The question would then be which of the competing standards to use. But, both ANSI and ISO standards are completely voluntary. No tile maker is bound to observe them. And, many don't. Ceramic tile may legitimately be called porcelain even if it is not "impervious" as long as it does not claim to meet the ANSI (or ISO) standard for porcelain.

So, this attempt by the standards organizations to create a universal standard for the use of the word porcelain as applied to ceramic tile has really had very little effect except to further muddy the waters.

Many tile makers ignore these new standards, especially traditionalist manufacturers in Europe and South America who still adhere to the older color-based, definition of porcelain tile. And, while American tile manufacturers have tried mightily to get the ANSI definition enacted into federal law, our honorable congress-people4 have so far been busy with much weightier matters — primarily getting re-elected and calling each other names.

How to Actually Buy Tile
As the situation now stands, the use of the word porcelain to describe ceramic tile has been left entirely to the discretion of individual tile manufacturers. How and when they use it is completely up to them. As a result, when the word appears on a box of tile it is often not possible to discover what it actually means. It may legitimately mean ...

A light bodied tile of any quality,
A high quality (in it's manufacturer's opinion) tile of any color,
A tile rated "impervious" under ANSI standard A137.1
A tile meeting the definition of porcelain under ISO 13006.

So does the word "porcelain" printed on the box actually help you select a suitable tile? It tells you nothing about the color of the tile — porcelain in the American tradition can be of any color. It does not reveal anything about the quality of the tile — porcelain in the European tradition may be of any quality. In fact, it does not tell you much of anything useful about the tile. The term "porcelain" is ambiguous. If the tile meets any of the many definitions of porcelain, and its manufacturer elects to call it porcelain, then it is — legitimately — porcelain.

Glaze vs. Enamel
In the tile world, the glass finish applied to ceramic tile is called the "glaze". In the bathroom fixture industry, the glass finish is called "enamel" — hence the term "enamelware". The two terms mean exactly the same thing, but there is an historical basis for the different names.

Enamel Broach Contemporary Silver and enamel broach in the Art Nouveau style. Available from Amazon. The traditional term, going back to the 15th century in the jewelry-making trades, for glass applied to metal was "enamel". The process involves grinding glass into a powder (called "frit") which is applied to the metal, then fired to melt the frit. It is not only beautiful, but is the ideal material for protecting steel and iron from damage by water.

With something small like a broach or finger ring, enameling metal is fairly simple, but what about something the size of a bathtub? Industrial scale enameling was not possible until 1880s when American Standard and Kohler separately developed processes for coating large iron objects — giving birth to the modern bathroom fixture industry.

Following the old tradition, the glass coating was called enamel. When sanitaryware manufacturers began applying over-glaze to ceramic bath fixtures like toilets and sinks, rather than iron fixtures, like tubs, they kept the term "enamel" instead of adopting the pottery term, glaze.

Enameled bath fixtures were an immediate success. They were so superior to the earlier wood and metal products, that the old products were literally driven from the market within a decade.

Enamelware was durable, very sanitary, and easy to maintain; and became an instant hit with American homeowners of the late 19th century who were avid for anything hygienic and sanitary (See Arts & Crafts Styles: Craftsman, Prairie and Four-Square Architecture for more information).

Paint manufacturers soon took note of the reputation of sanitary enamelware in the public mind, and seeking to capitalize on the name, started calling some varieties of their more durable paints "enamel".

Fixture manufacturers were a little miffed when the paint guys tried to steal their glory, and fought it for years. They lost. Paint companies can call their paint "enamel". Today, sanitary fixture manufacturers refer to their glazing as "porcelain enamel" or "vitreous enamel" to distinguish it from that other enamel the paint companies sell.

Our best advice: ignore the term porcelain altogether when shopping for clay-fired tiles. Disregarding the largely made-up distinction between porcelain and other ceramic tile actually makes choosing tile much, much easier.

Concentrate on the size, pattern, price and color that works best for you in a tile rated for the use you intend it for. Ignore whether the tile body is tan, orange, red or brown. After the tile is installed you will usually never see the actual body of the tile. What you will see is the tile's glaze.

The Tile Glaze
Some fired clay tiles, quarry and saltillo tiles, for example, are not glazed. The color of the tile body is the color you see, so it makes a difference what clay was used to make the tile.

But, most ceramic tiles have a coat of opaque, glassy material on the face of the tile that we call the glaze.

There are emerging one-step (or "monocottura") processes in which the tile and glaze are fired at the same time. But, traditionally, glaze is applied after the biscuit is fired, then the tile is fired again to set the glaze. This is called a "bicottura" or double firing method. It's this glaze that gives the tile its color and texture, not the composition of the tile body. The glaze is the tile's paint.

Think of wood siding. You don't see the wood in your siding. What you see is the coating on the wood — the paint. Most likely you don't even know what kind of wood was used for your siding, or if it was wood at all. It may be Masonite® or one of the more contemporary products, fiber cement siding, for example, which is a wood fiber and portland cement composite.

The same is true of glazed tile. Once tile is installed you can't see the tile body, you see only the glaze. So what difference does it make if the tile body is white, sand, terra-cotta or puce? If you need to go around a corner where the edge of the tile will be exposed, there are special edge tiles made just for that purpose. And, if you can't find a matching edge tile, your tile setter has a few tricks to disguise the edge.

By the way, we have heard mentioned from time to time that the glaze on good porcelain tiles has more "depth" than that on ceramic tiles, but that's just another nonsense myth. 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 yet another of those fables surrounding porcelain tile that just won't go away.

How to Read a Tile Label
Once you have found the color and pattern of a tile that you like, then all the other information you need to assess the usefulness of the tile is printed somewhere on the box, often in the form of icons. These icons tell us all about the tile, and since their use is regulated, the information in the icons is probably not going to be just marketing hype.

Let's see just what these icons can tell us.

Tile Grade
Grade Icon
Tile grade is the result of a visual inspection. The range is 1 to 3, the lower the number the better the tile. A grade 1 or Standard Grade tile exhibits no obvious imperfections when visually inspected at a distance of 3 feet. A grade 2 tile shows no visible imperfections at a distance of 10 feet. Almost all tile in a tile store will be grade 1. Sometimes you will find grade 2 tile on a "special purchase" sale — often at quite the discount. Grade 2 is just fine for many applications. The durability of a grade 2 tile is usually not suspect, it merely has visible imperfections. We sometimes use it in historical renovations to simulate 19th century tile that often had many visible flaws. Grade 3 tile is rarely seen in retail stores. It usually has major aesthetic problems including wide variations in tone and sizing. Let the tile professionals buy this tile. They know where and how to use it.
Wear Resistance
PEI Icon
This is the result of the PEI wear test that we introduced earlier (See chart above). Many manufacturers use this test only on floor tiles. The higher the rating, the more wear-resistant the tile. A tile used as flooring or on a countertop should be rated at least in Group II (light traffic floors). A higher rating is even better for floors with medium or heavy traffic. It should also be at least 1/4" thick. Thicker is generally better. If the tile is glazed, then it is the glaze coating that is tested. If the tile is un-glazed, such as in quarry tile, the tile body itself is tested. The tests are slightly different. If this rating is missing, the tile is probably not intended for floors — and will usually say so right on the box.
Water Absorption
WA Icon
This is the score the tile received on the ANSI test for resistance to water penetration (See chart above). A tile that is installed outdoors where there is a real Winter should not absorb water. Otherwise, water trapped within the tile may freeze, fracturing and cracking the tile. Almost all tiles rated impervious will work outdoors, but so will some vitreous tiles. Look for the frost rating (see below). For indoor applications, semi-vitreous and vitreous are strong enough for floors, and non-vitreous for walls.

All tiles called "porcelain" do not necessarily rate "impervious". Don't rely on the word "porcelain" on the box, look specifically for a frost rating or a W.A. score of "impervious". Some hardy tiles intended for use outdoors will have both. If there is a PCTA certification of "porcelain", then the tile has been tested for water absorption and found to be impervious, and this certification is a substitute for a W.A. rating of "impervious".
Slip Resistance
COF Icon
For floor tile, this Coefficient of Friction (COF) ranking is important. The test establishes how much force is required to move an object across the face of the tile, dry or wet. It tells you how resistant a tile is to slipping. The higher the score, the more slip-resistant the tile. Tile COF can be rated "wet" or "dry". For a general floor, both ADA and OSHA require a dry rating of 0.6 and above for a dry floor to be considered "safe". For a bath or kitchen, where the floor is likely to get wet, a wet rating of 0.6 or greater is required and 0.7 or higher is better. Some tiles specifically designed for wet floors are rated above 0.85 wet.

COF is an important consideration, especially in wet areas. One of my neighbors ignored COF when selecting impervious tile for his front stoop, and now, on wet days, you have to tip-toe over the tile with a death-grip on the handrail to avoid major injury.

There are problems with this test, however. The testing process involves pulling a weighted board with a Neolite (rubber) sole (used to simulate the bottom of a shoe) along the surface of a test tile. This is called a static slip test. However, the way we walk involves more than just slip-sliding along. There is both downward and outward force applied with each step we take. The standard slip test tells us nothing about the effects of these forces.

To test downward and outward force, what's needed is a kinetic or "dynamic" test. There are a number of dynamic resistance tests, but none has yet been approved for testing tile in the U.S. The most widely accepted test in Europe is the ramp test (DIN 51130) developed in Germany. The test involves a person walking along a platform of tiles that are being tested. The incline is then increased to a point where the person slips. Obviously, since people react differently when anticipating a slip — including changing their stride and walking more carefully — and some acrobatic individuals can airily skip down slippery slopes that would kill us clutzier types, this test has some basic reliability problems. It has not been adopted outside of Europe.
Breaking Strength Breaking strength is important for floor tiles. When you step on a tile, you don't want it to crack. The tile industry uses ASTM C648-04 to determine the strength of the tile. A force is applied to an unsupported portion of the tile specimen until it breaks. The tile's breaking strength is stated in pounds of force applied. A tile for use on floors must have a breaking strength of at least 250 lbs. Higher is better. This rating is typically not printed on the tile box or data sheet. It is simply assumed if the tile is intended for floors. You may have to telephone the tile company to get this rating.
Chemical Resistance Chemical resistance is measured using ASTM C650-04. A tile sample is placed in continuous contact with a variety of chemicals for 24 hours, rinsing the surface and then examining the surface for deterioration and visible color or texture variations. This is a pass/fail test. If there is any change in the tile, it fails and is usually not even put on the market or it is sold subject to limitations printed on the box or specifications sheet.
Stain Resistance Stain resistance of ceramic tile is testied using a process specified in ASTM C 1378. Various staining agents are placed on a minimum of five sample tiles. Each staining agent must remain on the samples, for at least 24 hours. They are then removed. The tile is rated by the strength of the cleaner required to completely remove the stain.
ClassStain completely removed with ...
5Hot water
4Weak cleaner
3Strong cleaner
2Solvent specific to the staining agent
1Stain not removed
Tile must test at class 3 or higher to pass — the stain must be completely removed with, at most, a strong cleaner. Typically the result is reported as merely pass/fail.
Freeze Resistance
If present, the "Frost" icon merely tells you that the tile is able to withstand repeated cycles of freezing and thawing. If there is no frost icon, it may mean that the tile is not suitable for use outdoors in any place where it might freeze, or the tile maker did not bother to order the test. Some tiles rated "vitreous" in the water absorption test will pass the frost test, and almost all "impervious" tiles will pass.
Tone & Shade Uniformity
The tone and shade rating is an indication of how much variation there is in the color and shade of the tile. The range of ratings on this V-scale is V0 to V4. V0 (monochromatic) indicates no visible color or shade variation among the individual tiles.
V1 Rating V1 (Low) indicates low visible shade and texture variation within each carton. V3 Rating V3 (Medium) indicates a medium shade and texture variation within each carton.
V2 Rating V2 (High) tiles show distinguishable differences in texture and pattern within each color. V4 Rating V4 (Random) file contains random variations of shade and texture within each carton.
Grades V3 and V4 need to be continually blended during installation to insure optimum appearance. This generally results in higher installation costs. Also, examine more than one tile, and more than one box of tiles to see if you like all the various tones. There may be considerable variation between cartons.

Some Informal Quality Tests
How did we tell good tile from not-so-good before there were these helpful package ratings? There are traditional tests that can be used to help judge the quality of a tile. Here are some rule-of-thumb tests that have been around for many years.

The Weight Test Hard fired tile is generally denser and therefore heavier than softer tile. You probably can't judge comparing single tiles, but heft the boxes. The heavier box is usually the harder tile.
The Ring Test Hold a tile between your thumb and forefinger at one corner and let it dangle. Snap near the opposite corner with your fingernail. A well-vitrified file with a high crystallization content will ring like a lead crystal glass. The sharper and higher the ring, the more vitrified the tile. If it goes "thunk", think of it as wall or backsplash tile.
The Color Test Hard fired terra-cotta tile is generally browner. We don't know why. It may be the composition of the clay or the fact that high firing turns the clay browner. And, it's not always true. But, generally hard fired tile is browner.
The Completely Unofficial and Totally Unap­proved Kinetic Slip & Fall Field Test The COF rating indirectly tells you whether a tile is slippery, but it's not 100% reliable. The most accurate test is our "Completely Unofficial and Totally Unapproved Kinetic Slip & Fall Field Test". It is a simple two part test.
  1. Carefully place several tiles on a hard, level floor, well supported so they do not tilt or wobble.
  2. Walk on the tile.
If you slip and fall, the tile fails the test. Don't buy it, and call your lawyer. If you need a wet kinetic slip test, toss some water on it first. The tile store clerk will probably go batty when you do this, but if you want to be completely satisfied that a tile is not slippery, do it anyway. We do.
The Informal Moh's Scratch Test In 1882 a German mineralogist, Friedrich Moh's, developed a table of relative hardness of minerals which has since become well-known as the Moh's Scale. Each mineral was given a number, with talc, the softest mineral ranked as 1, and diamond, the hardest, ranked 10. The minerals are:

Test Material
Test Material
10Diamond 5ApatiteWindow Glass
9Corundum 4FluoritePocket Knife Blade/Steel Screw
8Topaz 3CalciteCopper Penny
7QuartzCase-hardened Steel File 2GypsumFingernail
6Orthoclase 1Talc 

Each mineral in the table will scratch any mineral ranked lower in the table, but will not scratch any mineral ranked higher. Since most of these minerals are a little hard to come by in daily life (just what is "fluorite" or "orthoclase" anyway?), substitutes are generally used for the informal Moh's scratch test. These are shown in the table above. The substitute will scratch any mineral lower than its place in the table, but will not scratch any material higher than its place in the table.

Wall tile should have a Moh's scratch resistance of at least 4. You should not be able to scratch it with a copper penny. Floor tile should be at least 6 (7 is better in high traffic areas). You should not be able to scratch floor tile with a piece of ordinary window glass. If even a case-hardened steel file does not scratch the tile, it's some kind of alien super-tile, possibly escaped from a secret government lab in Area 51. Check for radiation!

Test Material
Test Material
10  5Natural GraniteWindow Glass
9  4Ceramic Wall Tile, MarblePocket Knife Blade/Steel Screw
8Engineered Quartz 3Site-Finished Wood FlooringCopper Penny
7 Case-Hardened Steel File 2Vinyl FlooringFingernail
6Ceramic Floor Tile 1  

For comparison,
  • Vinyl floor tile and vinyl sheet flooring is Moh's 1-2. You can dent it with a fingernail.
  • Site-finished wood flooring is Moh's 3-4 and can be scratched by a steel screw or pocket knife, but not with a fingernail, and rarely with a copper penny.
  • Marble is also typically Moh's 3-4.
  • Engineered quartz countertops are around Moh's 7-8 — tough stuff that can be scratched only with a case-hardened file.
  • Natural granite tops out at Moh's 4-5. Some can be scratched with window glass, but not with a pocket knife.
  • Do not scratch a tile without the store clerk's permission. If the clerk does not give you permission, buy just that one tile, then see what will scratch it before committing to more.

    You may not have to scratch it at all if the tile maker has conducted a formal Moh's test and printed a Moh's rating right on the box, and many tiles do. The rating is stated as a number from 1 (softest) to 10 (hardest). Values of 4 or more are suitable for walls and backsplashes, 5 to 7 for most floors. For very highly trafficked areas, of if hubby wears his golf shoes in the house, consider a Moh's value of 8 or higher.

    These rule-of-thumb tests should not be relied on by themselves. Read the ratings on the box. But, you can use these to impress the sales clerk with your deep and comprehensive knowledge of fired clay tiles. It also helps to throw around words like "monocottura" and "bisque" while you're at it, and refer frequently to ANSI A137.1 and wet and dry COF. You'll have the guy on the run after just a few minutes.

    Choosing the Right Tile for Your Application

    So, now you know a lot of rules and a few little tricks about ceramic tile, but you are probably asking yourself how you can apply the rules to make the best decision about buying tile for your bathroom, kitchen or sun room. Do you need PEI Group II or Group III, Vitreous or Semi-Vitreous? And, how about that Coefficient of Friction thing?

    Well, here's the table that shows how to put your new, in-depth tile knowledge to practical use in selecting the right tile for the particular use or application you have in mind. keep in mind that the table depicts the ideal tile for each application. Some of the combinations are probably not going to be found in the tile store. For example exterior walls call for a water absorption rating of "impervious", but a wear rating of just group I or II. Most likely you will have to move up to a Group III or IV because it is almost impossible to manufacture a tile that both impervious and soft. Chemically it cannot be done. So the lowest wear grade you are likely to find in an Impervious tile is probably Group III. More wear resistance than you need, but it's what's actually available.

    Ceramic Tile Application Guide
    Minimum ratings for the application specified.
    You can always step up to a higher rating, but expect, then,
    to pay more for features you may not need.
    Applica­tion Environ­ment Foot Traffic ANSI Water Absorp­tion Rating PEI Wear Resis­tance Rating2 Minimum Coeffic­ient of Friction For Use In…
    Dry Area   Non-vitreous Group I or II3   Tile wainscots, fireplace surrounds. Areas that rarely if ever get wet.
    Wet Area   Semi-Vitreous Group I or II3   Kitchen backsplashes. Areas that may get wet on occasion, but are unlikely to see constant or standing water.
    Very Wet Area   Vitreous Group I or II3   Shower walls. Areas that may get wet frequently and/or are likely to see constant or standing water. Exterior walls in areas that do not experience a hard freeze (and in areas that do experience a hard freeze if the tile is frost rated).
    Exterior4   Vitreous (if frost rated) or Impervious1 Group I or II3   Exterior areas that experience a hard freeze in winter.
    Dry Area Light Non-Vitreous Group II 0.60 (Dry) Bedrooms. Rooms where there is usually no through traffic.
    Medium Non-Vitreous Group III 0.60 (Dry) Family rooms. Areas of through traffic or normal use.
    Heavy Non-Vitreous Group IV 0.60 (Dry) Hallways. Areas of constant through traffic or heavy use.
    Wet Area Light Semi-Vitreous Group II 0.60 (Wet) Laundry rooms. Areas where there is usually no through traffic that get wet on occasion, but are unlikely to see constant or standing water.
    Medium Semi-Vitreous Group III 0.60 (Wet) Kitchens. Areas of through traffic or moderate use that get wet on occasion, but are unlikely to see constant or standing water.
    Heavy Semi-Vitreous Group IV 0.60 (Wet) Kitchens with heavy through traffic. Areas of constant through traffic or heavy use that get wet on occasion, but are unlikely to see constant or standing water.
    Very Wet Area Light Vitreous Group II 0.60 (Wet) Guest baths. Rooms where there is usually no through traffic, that may experience constant or standing water.
    Medium Vitreous Group III 0.60 (Wet) Master or main baths. Areas of through traffic or normal use that may experience constant or standing water.
    Heavy Vitreous Group IV 0.60 (Wet) Busy bathrooms and shower floors. Areas of constant through traffic or heavy use that may experience constant or standing water. Exterior decks, patios and walkways that do not experience a hard freeze (and in areas that do experience a hard freeze if the tile is frost rated).
    Exterior4 Any Vitreous (if frost rated) or Impervious1 Group IV or V 0.60 (Wet) Decks, Patios, Walkways. Exterior areas that experience a hard freeze in winter.
    1. Impervious tile may also be called porcelain, but does not have to be. It's entirely up to the manufacturer.
    2. When in doubt about a rating, select the next higher rating. For example, if you are not sure whether your kitchen qualifies as a moderate traffic or heavy traffic area, go with heavy traffic and choose a Group IV tile over a Group III tile — just to be sure. Almost all tile is now glazed, and almost all glazed tile rates at least Group II on the PEI wear test.
    3. You will rarely find Group I tile at a tile store. It is usually sold for hobby and craft applications.
    4. Some tile rated "vitreous" in the water absorption test will also work outdoors in a hard freeze climate. Look for the "Frost" rating on the package.

    When Do You Really Need Porcelain?

    Porcelain is far too much tile for most applications, and just not worth the higher price for features you don't really need. When do you actually need porcelain? Well, it depends on what you mean by porcelain, but here is a rough guide.

    If You Mean High-Quality, Impervious Tile

    There is no indoor application that requires impervious tile. That's worth saying again: there is no indoor application that requires impervious tile. None. nada, zip, zero, zilch, bupkus. Outside, it's a different story.

    Outside the House

    If you are using tile on a patio or deck in the Yukon (or Nebraska), you need a tile rated for frost resistance so it will withstand the repeated freeze/thaw cycles of northern winters without cracking. Some tile rated "vitreous" in the water absorption test will stand an exterior environment in hard freeze areas — look for the frost rating. A tile rated "impervious", will almost certainly be suitable for exterior use, frost rating or not. but it does not necessarily need to be called porcelain. Ignore the word "porcelain", look for "impervious" or the frost rating to be sure of what you are buying.

    Inside the House

    Inside the house, impervious porcelain is simply more tile than you need. If you examine the Application Guide, above, you will find that the best grade of tile you are likely to need is "vitreous" with a wear rating of Group IV for your floors in high traffic areas (hallways, kitchens, entries).

    …If a tile is rated for the ap­pli­ca­tion you have in mind, it will out­last you, your house, my 1968 VW mi­cro bus (maybe), and your great-great-great-grand­child­ren's great-great-great-grand­child­ren. Any extra dur­abil­ity is just a waste of mo­ney… Even this level of durability is more than is needed for low traffic floors, walls, backsplashes, and other surfaces that are not heavily walked on. Semi-vitreous and Group III are likely more than enough. If the tile is on a wall in an area other than a bath or kitchen, then most likely non-vitreous and Group I or II will work well enough, although, frankly, you will seldom find a tile rated in Group I in a tile store. You will have to go to a hobby or craft store to buy this grade.

    You can, of course, buy impervious tile for inside your house. Just expect to pay more for durability features you won't need. It's like buying a car. If you need to get to work, to the store and to church on Sunday (or Saturday, as the case may be), you don't need a Ferrari. It would be nice to own one, and you can certainly buy a Ferrari if you don't mind the budget-walloping cost of a Ferrari, but you are not likely to use the extra features you are paying for, like 200 m.p.h. on the flat or zero to 100 in 3.4 seconds. For what you are going to use it for, a Chevy is car enough.

    The same is true of ceramic tile. The most economical approach is to buy just the features you actually need. Sure, impervious tile is harder and more durable and will last nearly forever — it's the Ferrari of tile. But, do you need a tile that will last nearly forever, or can you get along with one that will last a mere 500 years or so?

    If a tile is rated for the application you have in mind, it will outlast you, your house, my 1968 VW micro bus (maybe), and your great-great-great-grandchildren's great-great-great-grandchildren. Any extra durability is just a waste of money that you could be using to upgrade your faucet, buy a better bathtub, or splurge on a romantic dinner for two at Vincenzo's. Don't forget that ceramic tile found in Pompeii has lasted over 2,000 years, survived at least one volcano, and, by today's standards, is truly crappy tile.

    If You Mean Light-Bodied Tile

    If by "porcelain" you mean a light bodied tile, then whether your need it depends on whether the tile is glazed or unglazed.

    Glazed Tile

    Glazed light bodied tile has absolutely no place, purpose or function in the world. We have never in 40 years of remodeling found a use for a through- or light-bodied glazed tile. Not once. Not ever. If the tile is glazed only the glaze will show once the tile is installed, so the color of the tile body makes absolutely no difference whatsoever to the appearance of the installed tile.

    Unglazed Tile

    If the tile is not glazed, then it's a different story. The color of the body is the color you will see, and if you need a light colored tile, traditional light-bodied porcelain may be your answer. One common interior application is mosaic floor tile which is often not glazed (to reduce slipperiness). This was a tile frequently used for bathroom floors in Victorian and Craftsman bathrooms — most often in bright white — so we use a lot of it in reproductions. Light-bodied porcelain used to come primarily from Italy, and it was pricey. Now days its made almost everywhere, and the price has dropped dramatically.

    The Bottom Line

    So, here's the bottom line:
    1. There is no indoor residential application that actually requires impervious porcelain tile — absolutely none. If your tile seller says different, he is a big fat liar, liar, pants on fire.
    2. Light bodied porcelain is appropriate where the body will show and a light body color is desired. If the tile is glazed, however, the color of the body makes no difference. It it will not be seen after the tile is installed. So, paying extra from full-bodied or light-bodied glazed tile makes no sense whatsoever.

    The Three Tile-Buying Do's and Don'ts
    So, at the end of all this discussion we end up with just three simple rules for buying fired clay tile.
    Don't pay any attention to the word "porcelain" on a box of tile. It does not tell you anything particularly useful.
    Do read the ratings on the box. Even if there are no handy icons, the ratings are probably in the fine print somewhere. If there are none, pass it by. You do not want to buy untested tile because you have no idea what you are getting. If you have questions about a rating or whether a tile will work for the application you have in mind, ask them of the manufacturer, not the clerk. The clerk probably knows less about it than you do after reading this article.
    Don't buy a better tile than you need. If you buy an impervious tile for your shower walls, you have probably paid more for features you don't need such as very high wear and frost resistance. A semi-vitreous tile would work just as well, and most likely cost less. Of course, if you just found the tile sale of a lifetime, forget all this and splurge, splurge, splurge.

    So, is it Porcelain or is it Ceramic?
    We don't actually care, do we?

    As we have seen, a tile deemed "porcelain" by its manufacturer is not necessarily better, harder, more durable, more scratch resistant or even always more expensive than a 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 game that dates back beyond the ancient Greeks to the even more ancient Chinese.

    The only two things that actually matter are whether you like the look of the tile and whether it is rated for how you intend to use it. A tile rated for the application you have in mind will work whether the manufacturer chooses to call it porcelain or not.

    So, if the tile salesman tries to "upgrade" you to a more expensive "porcelain" tile, look bored and yawn a lot. You know that there is no practical difference between ceramic and porcelain tiles. Ah, what the hell, "accidently" drop a box of tile on his toes for trying to trick you — deceivin' scoundrel that he is.

    A Little Something to Take to the Tile Store
    OK, so now you know how to buy tile. If you read this article carefully, you also know more than 95% of tile store clerks. So now for the piece-de-resistance, here is our handy How To Read a Tile Label crib sheet that you can download and print to take with you to the tile store.

    And, don't forget your "tile expert" testing materials: pocket knife, small shard of window glass, copper penny and the ever necessary tap water, cleverly disguised as bottled drinking water. No one will suspect. (By the way, don't try to go through airport security or into a federal building with this stuff in your pocket or purse. At very least you will be asked a lot of questions by large, humorless men in blue blazers.)

    Happy tile hunting. Let us know how it works out. And, don't forget leave your comment, below. Also, take a look at our other in-depth articles on remodeling topics and issues. The complete list is in our Index to Articles. Have fun. We do.


    1. This confusion is not new. Over 100 years ago William Burton was already complaining that the word porcelain was being applied to such diverse materials that it had lost all meaning. See: Burton, William, Porcelain, Its Nature, Art and Manufacture, B. T. Batsford Ltd., London 1906, pp. 47–48. Available on line and as an e-book, courtesy Google Books.

    2. The Venetian explorer, Marco Polo is reputed to have been the first to use the word porcellana in print to describe ceramic pottery c. 1298.

    3. The process of transforming a clay paste into ceramic tile through firing is one of the most complex in industrial chemistry, involving a number of what chemists call "structural transformations" of kaolinite and silica materials. Kaolin becomes metakaolin at about 1,100° F begins to form mullite at about 2,000°. As the temperature continues to rise, silica in the paste is is transformed into molten glass. Mullite and glass in its various forms are the major constituents of fired ceramics. The Kaolin clay transformed into mullite gives the tile its characteristic strength, structure and shape while the glass helps it resist water penetration.

    4. "In my many years I have come to the conclusion that one useless man is a shame, two a law firm, and three or more a Congress." -- Attributed to John Adams, second President of the United States.

    Rev. 02/15/15

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