Ceramic tiles are thin, flat tiles that are usually shaped with beveled edges. They are used for lining or covering a surface, and may provide corrosion resistance, thermal protection, wear resistance, and/or surface decoration. Ceramic tiles come in many different shapes, sizes and colors. They are secured to a surface such as a subfloor with mortar. The spaces between the tiles are filled with group. In flooring applications, cross-shaped plastic spacers are used to separate the tiles prior to grouting. There are many different types of ceramic tiles, both in terms of categories and features. Examples include waterproof, mosaic, ribbed, vitrified, quarry, saltillo, terra-cotta, earthenware, stoneware, and others.
Ceramic tiles are durable and hard wearing, making them suitable for covering surfaces such as roofs, floors, walls, table tops, bathroom showers, and other objects. Most ceramic tiles are categorized by the Porcelain Enamel Institute (PEI) according to their wear resistance. For example, PEI Class 1 tiles are only for wall applications; they are not suitable for foot traffic. PEI Class 2 tiles can handle light traffic, such as in residential bathrooms. PEI Class 3 tiles can handle light-to-moderate traffic, and are suitable for residential floors. PEI Class 4 tiles are for moderate-to-heavy traffic, and can be used in medium commercial or light industrial settings. PEI Class 5 tiles can handle heavy to extra-heavy traffic, making them suitable for all types of commercial and industrial floors.
Ceramic tiles are rated for scratch hardness according to the Mohs scale, which was named after German mineralogist Friedrich Mohs. The Mohs scale measures the ability of ceramic tiles to withstand scratches from a variety of minerals, ranging from the softest (talc) to the hardest (diamond). Ceramic tiles that are designed for residential use typically have a rating of 5. Ceramic tiles that are designed for industrial or heavy traffic areas have a rating of 7 or higher.
Manufacturers of ceramic tiles may use proprietary mixtures of elements to make products. Typically, however, all of these mixtures include clay mixed with sand, feldspar, quartz, and water. All of these ingredients are mixed in a mill to create a substance called body slip. The body slip contains approximately 30% water at this point, until it is heated and dried to reduce the moisture content to about 6%. The body slip has the appearance of dust or powder and is compressed into the ceramic tile shapes using a high pressure electric or hydraulic press.
After pressing, the formed tile shape is called bisque. The bisque tiles are dried to remove the remaining moisture. Some ceramic tiles remain unglazed, but most are glazed using a glassy substance that contains a mix of pigments that give the ceramic tiles their color and surface characteristics. Glazed ceramic tiles are fired in tunnel kilns or roller-hearth kilns at temperatures of approximately 2000 degrees Fahrenheit, permanently fusing the glaze to the surface of the tile.
There are two special types of ceramic tiles for use outdoors. Vitrified tiles have been treated to have very low porosity, making them strong and stain resistant. Impervious or porcelain tiles are fired at very high temperatures, making them very dense. Porcelain ceramic tiles have a high impact resistance to minimize breakage. Both vitrified and porcelain ceramic tiles are able to withstand the freezing and thawing conditions of outdoor applications. Other specialty types include pre-grouted ceramic tiles, which come from the manufacturers in large, pre-assembled sheets for quick installation.