American Olean
Shaw Ceramics

Ceramic tile basics

Ceramic tile is simply a mixture of clays which have been shaped and fired at high temperatures resulting in a hard body. This hard body may then be left untreated or it may receive a glazed wear layer. To put it a different way, ceramic tile is nothing more than beautiful, baked clay.

Despite its apparent simplicity, there’s actually a great deal to know about tile before you make your selection and install it in your home or business. We’ve divided this article into five parts to make it easier to get through:

  1. Durability
  2. Tile Density
  3. Tile Variations
  4. General Tile Characteristics
  5. Substrates
  6. Ceramic Tile FAQ

Part 1: Durability

A discussion about durability should precede other basic information about ceramic tiles. That’s because it’s important that customers first access their needs and make sure they’re selecting a tile with the necessary durability. Luckily, tile is rated, which eliminates the guesswork when it comes to making a selection.

PEI Wear-Rating System

To avoid inappropriate installation, most manufacturers use the following PEI (Porcelain Enamel Institute) guide to rate the durability of their tile. In the PEI system, Group 1 represents the least durable tile and Group 5 signifies the most durable.

  • Group 1 Tiles suitable only for residential bathrooms where softer footwear is worn.
  • Group 2 Tiles suited to general residential traffic, except kitchens, entrance halls, and other areas subjected to continuous heavy use.
  • Group 3 Tiles suited for all residential and light commercial areas such as offices, reception areas and boutiques.
  • Group 4 Tiles suited for medium commercial and light institutional applications such as restaurants, hotels, hospital lobbies and corridors.
  • Group 5 Tiles suitable for heavy traffic and wet areas where safety and maximum performance are a major concern. Used in exterior walkways, food service areas, building entrances, shopping centers and around swimming pools.

IMPORTANT: The wear rating of tile has nothing to do with its quality or price, only its durability. Some of the most expensive and luxurious tiles in the world rate only a 1 or 2.


The glaze applied to some floor tiles is simply a liquid glass that has been sprayed or poured onto the surface of the tile. It is then fused and hardened by means of tremendous heat.

Glaze colors are created by mixing a variety of minerals, including gold, silver, zinc, copper, mercury, cobalt and many others. The strength and wear resistance of the glaze depends on its hardness. The harder the glaze, the better it will stand up to pressure and abrasion. Glaze hardness is determined by:

  1. Temperature - the higher the kiln (oven) temperature, the harder the glaze.
  2. Color - light-colored glazes are usually harder than darker-colored ones.
  3. Gloss Level - matte- or satin-finished glazes are generally harder. Shiny glazes are usually softer and less durable.

The Clay

The baked clay body, which is also called a bisque, is made up of various types of clay and other minerals. Combined, these raw materials give the bisque its strength and stability.

The strength of the bisque is also determined by its density. The strongest bisques have the greatest density, which is characterized by the smallest and fewest number of air pockets in the clay. High-density tiles are suited for heavy commercial installations as well as residential projects.

The density of the clay also determines if the tile is suitable for outdoor use. Low-density tiles that are too porous and absorb more than 3% moisture will freeze and crack if installed outdoors in cold climates.

Part 2: Tile Density

The density of the tile is measured by the amount of water it absorbs. Based on that amount, a tile falls into one of four categories. Those categories determine whether a particular tile is appropriate for indoor or outdoor use. Remember, a higher density bisque, one with only a few air pockets, results in a stronger flooring tile. High-density tile is also more suitable for outdoor use because it will absorb less moisture and be less prone to cracking in freezing temperatures than porous, lower density tiles (those absorbing more than 3% moisture).

Tile Density Classifications:

  • Non-vitreous tiles absorb 7% or more of their weight in water. They are suited for indoor use only.
  • Semi-vitreous tiles absorb 3% to 7% water and are suitable only for indoor use.
  • Vitreous tiles absorb 0.5% to 3% water and are considered frost-resistant. They are suitable for both indoor and outdoor use.
  • Impervious tiles are the strongest available. They absorb between 0 and 0.5% of their weight in water. These frost-resistant tiles are appropriate for indoor and outdoor uses.

Types Of Ceramic Tile:

Ceramic tile is available for flooring in both glazed and unglazed forms.

Glazed tiles are made exactly the same way as unglazed tiles, but they undergo an additional process. A glass wear layer is applied then subjected to tremendous heat in a kiln. This process liquefies the glass and fuses it to the bisque.

Glazes offer an unlimited array of beautiful colors and designs and create a surface that is practically stainproof. While appropriate for uses that range from light residential use to medium commercial traffic, most glazed tiles are not considered suitable for heavy duty commercial use.

There are a few glazes, thanks to recent technological advances, that are now hard and durable enough to stand up to the most demanding commercial applications.

Unglazed tiles are simply baked pieces of clay whose colors are determined by the mineral content of the clay. These tiles are the workhorses of the industry. Generally thicker and denser than glazed tiles, they include products such as quarry tiles and porcelains. The rugged surface texture and matte finish of the these tiles give them good slip-resistant qualities for use in wet areas.

The toughness of unglazed tiles make them ideally suited (but not limited to) extra heavy commercial installation.

Colors, which are limited to the natural colors of the clay, range from light sand to darker red brick tones. To increase the color range, manufacturers achieve a wide range of beautiful colors by mixing color pigment in with the clay.
Popular unglazed tiles include:
Quarry Tiles:

Made from natural clays and shale, these unglazed tiles are generally in earthtone colors ranging from light tan to reds. Some manufacturers have increased the color range by adding color pigments to the clay.

The body of a quarry tile is thick and dense with good slip resistance, making them a popular choice for both heavy commercial and residential installations.
Porcelain Tiles:

Porcelain tiles are made up of special clays and minerals similar to those found in chinaware. The special clays allow the tiles to be fired at extreme temperatures (2500 degrees F), resulting in a denser and harder body than most other tiles. Highly stain-resistant and strong, they are available with plain, rough or polished finishes.

The combination of beauty and durability makes them ideal for heavy commercial and residential installations.
Terra-Cotta Tiles:

Terra-Cotta Tiles are either handmade or machine-made.

Handmade terra-cottas are usually crudely made and not appropriate for outdoor use in all geographic areas except those that are hot and dry year-round. The most popular handmade tile is the Saltillo tile from Mexico. These tiles vary widely in size, shade and texture from one another, which many customers believe adds to their charm. Occasionally, they will even be marked with animal tracks.

When used indoors, they must be sealed and waxed in order to prevent staining and wear. Colors range from terra-cotta to yellow and brown. Additional colors can be achieved with stains.

Machine-made terra-cottas are much denser. Because their increased density makes them frost-resistant, they can usually be installed outdoors.
Mosaic Tiles:

Mosaic tiles are usually less than 6 square inches in size, and generally come mounted on perforated paper sheets or latex mesh for easy installation.

Very dense, tough and stain-resistant, mosaics are ideal for countertops and wall tiles. They’re also great for shower floors, because their small size gives them the flexibility to follow the contour of the floor as it slopes to the drain. The numerous grout joints also aid in slip resistance.

While most quarry, porcelain, terra-cotta and mosaic tiles are unglazed, all of them can be produced with a glaze.
Wall And Floor Tiles:
Wall Tiles:

Any ceramic tile is suitable for walls, but those that are very thin, high-glossed and decorative are most commonly used. The most popular size for wall tile is still 4 1/4" x 4 1/4" but there appears to be a trend toward larger, more luxurious tiles.

Wall tiles have a very soft glaze and porous body and therefore should never be used on floors or for outdoor applications.
Floor Tiles:

Glazed or unglazed floor tiles have sufficient strength, impact and abrasion resistance to withstand weight and foot traffic. They are usually thicker, denser and heavier than wall tiles.

If the substrate is strong enough to support the weight, floor tiles may also be used on walls and countertops.
Gloss Levels of Floor Tiles:

Glazed ceramic tiles vary in gloss levels depending on the look the manufacturer wants to achieve. Options include matte, satin and high-gloss finishes. Generally, the higher the gloss, the softer the glaze. Areas of the home that don't receive heavy wear, such as bathrooms, can use a higher gloss level than high-traffic areas such as kitchens.

The information on specific product labels or literature will always list the proper areas to install the tile.

Part 3: Tile Variations

Throughout the ages, ceramic tile has been praised for its versatility. While carpet and vinyl are produced mainly for floors, ceramic tile can be used in countless applications. These possibilities include:

  • Floors
  • Walls (interior and exterior)
  • Countertops and backsplashes
  • Patios
  • Pools
  • Fireplaces
  • Walkways
  • Exterior house trims

Sizes, Shapes and Finishes

  • Floor tile sizes range from small mosaics of less than a square inch to 24”x24” tiles. In the United States, most floor tile measures 8”x8” or 12”x12”, but there is a growing trend toward larger tiles.
  • The most popular wall tile sizes are 4 1/4" x 4 1/4" and 6"x6", but there is a trend toward larger tiles such as 6" x 8" and 8" x 10".
  • Square tiles still dominate the market, but there are many other available, including rectangles, hexagons, elongated hexagons, octagons and many more.
  • Tiles also come with a variety of shaped edges, including straight, scalloped and cushioned edges that are heavily beveled to simulate handmade Mexican tiles.
  • Ceramic tile is also available in various surface finishes. These include smooth surfaces, textured surfaces that simulate slate or stone, undulated surfaces that imitate handmade tiles, and gritty surfaces for slip resistance.

Production Methods

  • Monocottura:

    This term is an important one to know because many people relate it to quality. Monocottura is an Italian word meaning "single-fired." This new method shapes, glazes and fires the tile in one step.

    The development of the Monocottura technology completely changed the industry for the better. The process dramatically speeds up production resulting in cost savings passed to the customer. Prior to the development of the Monocottura method, some tiles were baked in the kiln for days. Today, these tiles can be produced in less than an hour.

    Monocottura tiles also have a denser body and harder glaze compared to previous methods of production, which results in a more durable tile.

    Single-fired products are produced with a flat back which makes installation much easier than the old-fashioned button- or lug-backed tiles.

  • Bicottura:

    Bicottura means "double-fired" in Italian. The clay body is baked on the first pass, and the glaze is applied on the second. Actually, Bicottura tiles may go through the kiln as many as four times. This method of production has been replaced by the Monocottura method for making floor tiles for many reasons.

    Bicottura floor tiles have a softer body and weaker glaze than Monocottura tiles and are generally not recommended for outdoor use. Bicottura floor tiles are also produced with lugs on the back making installation more difficult.

    However, the Bicottura method is still considered by many to be the best way to produce decorative wall tiles in multiple colors.

    There are other methods of production, but these two provide the basis of what you need to know when making a floor tile purchase.

  • White Body vs. Red Body

    The clay used in glazed tile production is characterized as either white body or red body.

    While some people claim that one color or the other is superior, the quality of a tile has much more to do with the quality of the manufacturing process and the care taken during production.

    Shading and Sizing

    Many tiles, both unglazed and glazed, are deliberately produced with a wide shade variation to capture the natural beauty of the product.

    A certain degree of shade variation is inherent in all ceramic tile. To limit the amount of variation within a carton, manufacturers simply sort tiles and package similar colors together.

    To minimize any noticeable shade variations, installers generally work out of several cartons at the same time and blend tiles together.

    Tile sizes will almost always vary slightly. This is inherent with most tiles, and is concealed by grout joints. Most manufacturers will keep sizing to an acceptable level by sorting the tile by size prior to packing it.

    Although most tiles are advertised and sold in nominal sizes such as 8" x 8" or 12" x 12", the actual sizes will be more like 7 7/8" x 7 7/8" or 11 7/8" x 11 7/8".

    A good installer will usually not install tiles with size or shading variations that are too pronounced.

    Part 4: Tile Characteristics

    All ceramic tiles share unique and exceptional qualities found in no other type of decorative building products. It’s important to consider these characteristics and their variations as you make your selection.

    Abrasion Resistance

    How a tile's glaze or surface will hold up under continuous wear is a very important consideration when choosing a glazed floor tile. Commercial areas, as well as areas of the home subject to heavy use (kitchens, foyers), require good abrasion resistance. If the right tile is chosen and properly maintained, it can easily last for the life of the house.

    Unglazed tiles naturally provide the abrasion resistance necessary for safety.

    Water Absorption

    The glaze on ceramic tiles is nonporous. When referring to the water absorption of glazed tile, the reference pertains only to the tile’s body. The water absorption of glazed tiles is also important to know when selecting outdoor tiles. Any tile that absorbs more than 3% moisture, glazed or not, is not suited for outdoor use in cold climates where it may freeze and crack.

    Frost Resistance

    Frost resistance goes hand in hand with water absorption. The less water the tile absorbs, the greater its frost resistance.

    Stain Resistance

    In general, ceramic materials are among the most stain-resistant building products. Glazed tile and even some unglazed tiles resist practically all solutions that could cause staining in other types of products.

    Slip Resistance:

    The slip resistance of ceramic tile in ordinary applications is comparable to most hard flooring materials. And it is significantly better than some. Unglazed tiles have greater slip resistance than glazed tiles and are recommended for areas subjected to frequent water spills. Many glazed and unglazed tiles also feature an abrasive grit on their surface, increasing their slip resistance substantially. These tiles are particularly suited to public areas with direct access to the outdoors.

    Color Permanence

    While most colored materials will be altered by long exposure to light, the colors in ceramic tiles will not fade from light exposure.

    Dirt Resistance

    Ceramic tiles do not retain dust or residues. Plain water or a damp cloth is generally all that's required to keep the tile clean. With the exception of tiles such as terra-cotta, which may be optionally oiled or waxed, no polishing or buffing is necessary to maintain the finish.

    Fire Resistance

    Ceramic tiles are completely fireproof at any temperature. They will not burn or feed a fire. Their surface will not alter, nor will they give off any toxic gases, smoke or fumes during a fire.

    In addition to being fireproof, tiles have been found to provide protection for structural surfaces during fires.

    Part 5: Tile Substrates

    Substrate is the term used to describe the subfloors, subwalls and subcountertop. Preparing a good substrate is the most important step in ensuring a beautiful tile installation.

    General Requirements

    • New concrete subfloors must be left to cure 28 days before tiling.
    • All floor and wall substrates must be rigid. Any spring in the substrates may crack the tile.
    • All substrates, particularly floors, must be structurally sound.
    • All substrates should be flat and level or plumb.
    • All substrates must be completely free of oil, grease, dust, loose or peeling paint, concrete sealers or curing compounds. If these contaminants are not removed, the tile will not adhere properly to the substrate.

    Suitable And Unsuitable Substrates

    Suitable tile subfloors include those that structurally sound and free of excessive movement. They include:

    • Concrete (in good condition) (cured 28 days)
    • Terrazzo or natural stone
    • Ceramic tile
    • Non-cushioned vinyl and linoleum
    • Cement backer boards
    • Double layered plywood (exterior grade) combined 1 1/4"

    Unsuitable subfloors for tile are those that tend to flex, expand and contract or warp. Any excessive movement will loosen the tile and pop the grout. These subfloors must be replaced or covered with a suitable underlayment. Unsuitable subfloors include:

    • Cushioned vinyl
    • Perimeter installed vinyl
    • Single layered plywood
    • Flake board
    • Particleboard
    • Chip board
    • Hardwood (strip) flooring
    • Luan plywood
    • OSB boards
    • Masonite
    • Sheet metal

    For detailed information about appropriate installation, substrate types and conditions, special installation requirements, and setting materials, read the iFLOOR.com article entitled Selecting The Right Installation Method.

    Frequently Asked Questions

    The following is a list of the most common questions asked by customers:
    Q: Will ceramic tile chip and crack?

    Prior to installation, ceramic tile is very brittle. Once it is installed, it becomes a permanent part of your construction, and will not chip or crack unless struck with a heavy object.
    Q: How durable is ceramic tile?

    If the right tile is selected and maintained properly, that is, kept free of grit and sand, it should last the lifetime of your home.
    Q: What is the difference between glazed and unglazed tiles?

    Glazed tiles are coated with a liquid glass which is then baked into the surface of the clay. The glaze provides an unlimited array of colors and designs, and will not stain or fade. Unglazed tiles are essentially the same as glazed tile, except that their surface is not coated. Unglazed tiles do not show wear because their color extends throughout the tile, making them ideal for heavy traffic.
    Q: What types of tiles are used for outdoors?

    Any tile that is frost-resistant may be used outdoors. For safety reasons, only unglazed tiles with a slip-resistant surface should be used on patios, walkways, pool decks, etc. Glazed tiles should only be used on vertical surfaces when installed outdoors.
    Q: Isn't ceramic tile slippery?

    Tile is about as slippery as vinyl or wood. Naturally, if the floor gets wet, any of these hard surfaced materials will become slippery. There are many tiles that have slip-resistant surfaces, but the more abrasive the surface is, the more difficult it will be to maintain. You might consider using a mat in wet areas.
    Q: Should ceramic tile be waxed?

    Glazed tile should never be waxed. The purpose of the glaze is to give you a maintenance-free floor. To keep your tile looking new, use a small amount of neutral detergent in warm water, plus a clean rinse.
    Q: Should sealer be used on ceramic tile?

    Glazed tile is already stainproof, so sealers are not necessary. You may put a penetrating sealer on your unglazed tile. The penetrating sealer is an invisible, stain-resistant shield that is absorbed into the surface of the tile. We do not recommend using a surface sealer because it wears unevenly and requires constant touching up in traffic areas.
    Q: Isn't ceramic tile cold on the feet?

    Many people assume this, but it is not true. Ceramic tile is a thermal product that absorbs both heat and cold, depending on the room temperature. The tile stays cool in the summer and warm in the winter.