Technical properties

Regularity and structural properties

Regularity. The regularity of a batch of tiles depends on the dimension of the sides and on the planarity of the surface.
As regards the sides, you must ascertain they do not curve and that they are perpendicular to each other.
Planarity, which requires a more detailed measurement, is determined by the centre curvature, the edge curvature and the warpage.
The property of regularity, besides the size, also depends on the tile appearance that can show the following defects: cracks, crazing, glaze devitrification, unevenness, specks or spots, underglaze faults, chips, blisters, edge irregularities and glaze accumulation on the edges.
Structural properties. Water absorption is the characteristic that is used to describe the tile structure in a quantitative way. Such absorption occurs through material pores, which are in contact with the exterior surface, and thus directly indicates the structure of the material itself: a high level of water absorption corresponds to a porous structure, a low level to a compact structure.

Massive and surface mechanical properties

One of the main massive mechanical properties of tiles is the flexural modulus of rupture, defined as the maximum stress that the material can support before breaking. This property is related to the material structure.
Besides this modulus, the flexural breaking strength is also measured, determined not only by the material structure, but also by the dimensions of the tile (in particular, by its thickness), which indicates the ability of the tile to resist breakage when subjected to loads.
Another important property is resilience, or impact resistance. This property gives a measure of the resistance of the material when used for floorings, against breakage caused by dropped objects. Tiles, like all ceramic materials, are not resilient, but fragile, that is, they have a limited capacity to resist impact.
The main surface mechanical characteristic of tiles is resistance to abrasion, or to actions of wear connected to the movement of objects on the surface. These actions may generate two effects: the material is gradually worn, and/or the surface undergoes alterations with loss in shine, variation in the colour shading, a possible increase in surface porosity, etc.

Thermo-hygrometric and chemical properties

Frost resistance characterizes some types of ceramic tiles. This atmospheric phenomenon has a dual effect: the penetration of water, favoured by the dimension and presence of pores in the tile, is followed by a second phase if the temperature falls below zero, at which point the absorbed water solidifies. It is well known that when water solidifies – that is, turns to ic – the volume increases. As a result, frozen water in the tile pores can provoke stresses causing breakage and detachment in parts of materials not resistant to frost. It clearly exists a close relationship between resistance to frost and water absorption, in the sense that the more difficult it is for water to penetrate, the greater will be this resistance.
Thermal shock resistance.
Sudden temperature changes can damage tiles. Resistance to sharp and abrupt changes in temperature shows the ability of the tiles to withstand such events without undergoing damage. Thermal expansion is the property which describes how any material undergoes expansion when the temperature increases, and contracts when the temperature falls.
Crazing resistance.Crazing may occur in glazed tiles and consists in the formation of fine cracks in the glaze thickness.
The causes of crazing can be traced to a unsuitable (oppure “not appropriate”) dilatometric ratio between glaze and support. Resistance to the occurrence of these micro-cracks is a further property of glazed ceramic tiles.

Chemical properties

Among the characteristics of this type we can include resistance to the attack of aggressive chemicals that may corrode the surface and therefore alter the aesthetic appearance of the tile. Stain resistance, closely linked to chemical resistance, refers to the behaviour of a ceramic surface exposed to staining agents, and is measured as a function of the effectiveness with which stains may be removed. Stain resistance thus measures the “cleanability” of a surface.

Anti-static properties and behaviour in a fire

Ceramic tiles belong to the category of electric insulators. Their electrical conductance, reaches very low levels. This is a very important safety feature. For applications with particular anti-static requirements such as floors in operating rooms, laboratories, or chemical plants, special tiles are needed which are characterized by a greater electric conductance compared to conventional tiles.
Ceramic products can be considered as safe also in the event of fire. The behaviour of a material in a fire is defined by specific properties that can be classified into three groups: resistance to the destructive action of flames, the possible contribution the material may give to feeding the flames, and the emission of fumes or toxic substances in the event of fire.