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?• The European tradition that refers to any light-colored tile body as porcelain, no matter the quality of the tile; and• The American definition that refers to any high quality tile as porcelain, irrespective of the tile's body color.
|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).|
|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.|
"…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."
||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.
||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.
Floor tile 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.
||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".
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
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 — a floor you could not slip on even with great effort.
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 great bodily harm.
There are problems with this test, however. The approved testing process (ASTM C1028-07), 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. 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.
The static slip test has its own reliability problems. It often misreads the slipperyness of wet surfaces, showing them safe when in fact they are not. Both the Ceramic Tile Institute of America, and Tile Council of North America have acknowledged that the test is inadequate for assessing the slip safety of ceramic tiles. The most promising replacement is the Dynamic Coefficient of Friction test (DCOF/ACU). The testing protocol requires a BOT-2000 drag-sled meter that crawls along the tile under its own power at a constant speed measuring the resistance to slip of a standardized piece of rubber loaded into the bottom of the machine. The minimum acceptable DCOF test value for floor tile using this test is 0.42 wet or dry. Below .30 is considered unacceptable for floor tile.
At the moment many tile companies are using and reporting both the static slip test and the BOT-2000 test, but the expectation is that eventually the static test will be discontinued altogether.
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|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. And, if Uncle George, even after his last diet, still weighs in at a hefty 320 lbs. or so, higher is definitely required. 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 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 of ceramic tile is tested 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 24 hours. They are then removed. The tile is rated by the strength of the cleaner required to completely remove the stain.
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. Almost any glazed tile will easily pass this test. Of more concern are unglazed tiles such as quarry or saltillo tiles. When buying these tiles, you will want to know the tile's stain resistance class.
||The "Frost" icon merely tells you that the tile is able to withstand repeated cycles of freezing and thawing. And, that's how its tested. It is put through muliple freeze/thaw cycles to see if it will show damage. The result is reported as pass/fail. If it cracks, it fails. The body of a tile rated "impervious" in the water absorption test will almost always withstand repeated freeze/thaw cycles, but this may not be true of the glaze. Some glaze will "craze", i.e. form small cracks. This frost test subjects the glaze as well as the body of the tile to freeze/thaw cycles to see if both parts of the tile can withstand the stresses of Winter.
If there is no frost icon, it means that the tile is not suitable for use outdoors in any place where it might freeze. 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.
|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 Entirely 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 Entirely Unapproved Kinetic Slip & Fall Field Test. It is a simple two part test.
|The Informal Mohs Scratch Test||In 1882 a German mineralogist, Friedrich Mohs, developed a table of relative hardness of minerals which has since become well-known as the Mohs Scale. Each mineral was given a number, with talc, the softest mineral ranked as 1, and diamond, the hardest, ranked 10. The minerals are:
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 Mohs 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. So, a copper penny will scratch gypsum, but not fluorite, whatever that is.
Wall tile should be at least 4 on the Mohs Scale. 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!
You may not have to scratch it at all if the tile maker has conducted a formal Mohs test and printed a Mohs 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, or if hubby wears his golf shoes in the house, consider a Mohs value of 7.
Ceramic Tile Application Guide
(Minimum ratings for the application specified)
|Application||Environment||Foot Traffic||ANSI Water Absorption Rating||PEI Wear Resistance Rating2||Minimum Coefficient of Friction||Suitable For Use In…|
|Dry Areaalign="center" class="lead-paragraph"||N/A||Non-vitreous||Group I or II3||N/A||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.|
|Don't||pay any attention to the word "porcelain" on a box of tile. It does not tell you anything particularly useful.|
|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.|
|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.|