What is ceramic tile?
Simply defined, ceramic tile is tile made of clay. What is cement tile? Well you get the picture. Ceramic and cement based tile are similar in at least one respect, they both are often formed by similar means. That is where the similarity ends. After the formation of the tile body, ceramic tiles go through a firing process. Cement tiles are not fired.
All tiles start out in the earth. Raw materials are quarried and refined. In the case of ceramic tiles, this includes clays, talc, and other minerals. Obviously cement based tile include cements and sands. Great care is taken in the proper mixture of these materials, as each one is critical to the success, quality and characteristics of the product produced. Once the raw materials are quarried, prepared, and properly mixed, the tiles may now be formed.
The most common means of forming the tile bodies are:
This method is used for ceramic tile only. An almost dry mixture of clays, talc, and other ingredients are pressed into a mold at extremely high pressures.
This method can be used for ceramic or cement tiles. The ingredients are slightly wetter and are forced through a nozzle to form the desired tile shape.
SLUSH MOLD or WET POUR
This method can also be used for ceramic or cement tiles. A much wetter mixture of ingredients is poured into a mold to form the desired shape.
Cement or ceramic tile. Very similar to dust press method, except that the size of the tile shapes are generally much larger.
After the tiles are formed, they must be hardened. Generally this is where the cement tile manufacturing process separates from the ceramic. In the case of cement tiles, they harden through a process called hydration. The cement simply hardens. This includes whatever glaze the manufacturer chooses to use. In the case of ceramic tiles, they are fired in a kiln under very high (2000 degrees F.) heat to harden the tile body and to create the surface glaze, if any.
When ceramic tiles are formed, their moisture content can vary plus or minus 6%. Since moisture is the tile manufacturer’s enemy during the firing process, the tiles must be dried to within 1% prior to kiln firing. If the moisture content were not brought down to this level, the tiles would explode as the moisture within the tiles boiled and became pressurized gas. The drying process can be accomplished in ovens or in the open air. Once the drying process is accomplished, the tiles can be placed or moved through a kiln.
This brings us to an interesting point. Historically, unglazed tile was fired once. Glazed tile was fired twice. The first firing formed a tile body called a bisque then the tile was fired again after the application of the glaze material. In the automated world of tile manufacturing, a new process was developed by which the tile body and glaze could be fired simultaneously. This process was termed monocottura. Around the world tile is still manufactured using the single and double firing methods. The glaze, which is called frit, is essentially a glasslike substance and is applied by either spray or waterfall methods to the surface of the tile.
When the body of the tile does not possess as in the case of certain ceramic mosaic or quarry tiles, the use of an engobe is necessary. engobe is applied just prior to the glaze and imparts color or opacity to the tile body. The quality of the engobe is of paramount importance as it can prevent stains from reaching the visual surface of the tile from below the substrate or the surface the tile is mounted to. With this all said, we can move on to the types of kilns used today:
Oldest and slowest kiln in use today. The stacking of these tiles in beehive kilns makes the parallel lines you see on the edges of modern Mexican paver tiles.
Modern faster kilns in which tiles are placed on setters or kiln carts and paraded through the kiln in 8-10 hours.
ROLLER HEARTH KILNS
These are the fastest kilns in use today, in which tile is routed on ceramic rollers through a kiln in 45 minutes to 1 hour.
Whether the tile is fired once or twice or not at all in the case of cement tiles, each type of tile has certain characteristics. These characteristics determine what application the tile should be used for. The American National Standards Institute (ANSI) together with the American Society for Testing and Materials (ASTM) has established a method for testing ceramic tiles which is found in ANSI 137.1 1988.
ANSI 137.1 1988
The results of this testing procedure establish minimum standards for the various types of tile and trim. Also, the testing reveals certain characteristics of the tile such as:
- water absorption
- abrasion resistance
- impact resistance
- breaking strength
- stain resistance
- visual quality The water absorption characteristic is of particular importance as it places the tiles into one of four types of tile.
Type of Tile Water Absorption Potential
non-vitreous tile: +7.0%
impervious: less than .5%
The testing will result in the tile being placed in one of three categories.
Grade ANSI Requirements
Standard tile that passes all the minimum standards and will pass the visual examination at a distance of 3 feet.
Seconds will pass the minimum standards and visual exam at 10 feet.
Culls tiles that do not pass at all and are discarded or not used for their intended purpose.
What do the characteristics mean to you? They help determine what kind of tile you need for your particular application.
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