A Closer Look at Ceramic/Clay Tile
July 13, 2011
Ceramic flooring has been around for thousands of years, as evidenced by the many archeological dig sites around the world. It is one of the most durable of all flooring materials used today and, when you combine that with manufacturing innovations, it is no wonder that these flooring materials are making such an impact in the flooring market.
Although the ceramic/clay category consists of several classifications that have different properties and characteristics, they are often simply referred to as ceramic tiles. The word ceramic comes from the classical Greek work κεραµικός (keramikos), which means “of or for pottery.” The word tile comes from the French word tuile, which is an extension of the Latin word tegula, which translates to “roof tile composed of baked clay.”
The ceramic/clay category of flooring materials consists of several classifications which include ceramic, porcelain, quarry, brick and terra-cotta. All of the classifications within the category are made from natural clay, additives and water. The manufacturing methods used may be dust pressed or extruded and some can be glazed or unglazed. The properties and characteristics of all ceramic/clay flooring materials are generally governed by the manufacture process.
The manufacture of ceramic floor tiles begins by combining the raw materials; clays, feldspar, talc, shale, and others. The clay mixture is put into a ball mill (a mechanical device that uses ball bearings or rods to pulverize minerals) as it is mixed with water. The mixture at this point will be wet, which is fine for the extruded method of manufacturing, but for the dust pressed method additional processes must occur.
When the dust pressed method is used, the wet clay is fed through high pressure pumps to a silo where the clay mix is air dried with spray driers. When the clay mixture exits the spray drier it is no longer wet, but damp. The now damp powder is fed into a machine that presses it into the floor tile using very high pressure. The tile exits the pressing machine complete and ready to be fired. The extrusion process uses wetter clay that is fed into a mold. The mold is the shape and size of the tile. As pressure is applied the clay bisque exits the machine and is cut into individual tiles.
Regardless of whether the tile is dust press or extruded, it will be ready to be fired at extremely high temperatures. One firing may be used when producing unglazed tile and two firings may be used when making glazed tiles. Pre-mixed glazes are used to produce consistency in color, weight, viscosity and density. In essence unglazed tiles are pretty uniform throughout their body, but glazed tiles will have a layer over the surface that is basically a glass like crystalline structure.
The tiles enter the kiln for the firing process which is strictly controlled in terms of temperature, pressure and the length of time it spends in the kiln. The temperatures used to fire clay floor tiles can reach over 2,000 degrees F and the time in the kiln will vary depending on the type of tile being made.
The time in the kiln can make a significant difference; the more heat the tile is exposed to the more moisture is removed from the tile. This ultimately makes the tile much harder and more water-resistant. As the bisque dries the clay particles in the tile crystallize, the longer the product is exposed to the high temperature, the more water is evaporated and the more crystallization occurs. This process produces a dense, hard floor tile that is more resistant to water.
The two most important properties and characteristics of clay flooring materials are the durability of the product and the water resistance of the product.
Durability is measured by the resistance to wear classification that ranges from Group I, which is very soft tile that is not suitable for flooring material, to Group IV+ (V) which is the hardest tile that can be used for the heaviest commercial applications.
Different classifications of tile will have tiny air pockets in the product that will allow water to enter the tile. The water resistance rating of the floor tile is established by ANSI and is a test that measures the permeability by water.
Understanding the manufacturing process and how it impacts the properties and characteristics of ceramic/clay floor tile will help the technician to comprehend how the tile will perform and the environment best suited for the tile. This could be a huge help when confronted with the difficult challenges for floor maintenance on those floors.