Ceramic tiles are flat, thin items made of clay, silica, fluxes, colouring and other raw materials. They are generally used to pave floors and cover walls and façades.
The clay used to make the slab may be for red firing or white firing. Both the floor tiles and the wall tiles are impermeable ceramic tiles that are normally made using a clay slab and vitreous coating: ceramic glaze.
Tiles, anywhere/any place
The wide range of ceramic products currently available on the market is conditioned by the different uses of this construction material. Depending on their use, there are different types of products with different characteristics. They are currently used for floors and facing.
The manufacture of ceramic floor and wall tiles has undergone considerable and continuous changes over the past years. Ceramic wall tiles are normally porous, which favours their adhesion to walls. On the contrary, floor tiles have low porosity, with low-medium water absorption, which gives them better technical characteristics.
Traditionally, tiles were manufactured following different methods and by means of a practically manual process. As from the seventies, the process has gradually been automated and methods have been unified considerably, with dry pressing being the most common and allowing the product to be manufactured in two different ways:
Double firing process
In this process, the pressed body is fired to form a bisque and subsequently a glaze is applied on top of this and the body is once again fired to obtain the final finish.
Single firing process
In the single firing process, the glaze is applied directly on to the pressed and raw body; both are fired simultaneously to obtain the final finish.
For many years there has been a controversy with regard to which of the two methods is better. In fact, having the correct formulation of both the body and the glaze, and keeping strict control of all the manufacturing stages, it is possible to produce good tiles using any of the methods.
Traditionally the double firing process was used more, with firing cycles of forty and twenty hours for the first and second firing respectively (firing of the body and of the glaze). It is currently more convenient to follow the single firing process, with cycles that last only forty-five minutes.
Moreover, in addition to the economy of the single firing process, it is very easy to automatize the different manufacturing processes, which in turn results in cost reductions.
Ceramic floor and wall tiles are obtained by preparing a composition of purified raw materials comprising aluminous silicates, with different compositions in the case of floor and wall tiles in red body or in white body.
These compositions undergo dry or wet grinding until a fine grain size is obtained, after which they undergo granulation or drying by subsequent atomisation in order to obtain granules with defined characteristics (size, shape, apparent density, fluidity, etc.).
The granulated powder is the base for the obtention of the ceramic product and its homogeneity guarantees the constancy of the physical properties of these materials. The granules feeds a oleodynamic press with a force of 600 to 1400 MT, that forms the tile into the shape and thickness chosen, for which metallic moulds with the exact dimensions are available.
Subsequently, the shaped tiles are dried and glazed with several layers of glazes of different compositions and with optional decorations in accordance with the models available.
Once the tiles have been glazed and decorated, they are placed in an oven for firing in more or less quick cycles and high temperatures, depending on the type of product being manufactured. Maximum temperatures depend on the type of product to be obtained.
The ceramic glaze and decoration embellish the tiles and give them the technical superficial characteristics desired. In the case of ceramic wall tiles, these are impermeability, resistance to detergents, etc, and in the case of floor tiles, they are resistance to abrasion, acids and scratching, etc.
The techniques, process control requirements, careful design that meets the needs of each atmosphere and the care taken in classification, give the product homogeneous characteristics that are in accordance with the requirements of its use.