The surface hardness of ceramic tiles is the ability of the cladding surface to withstand the mechanical stress of other materials. For ceramic facing materials or natural stones, this property is usually indicated in accordance with the mineralogical scale of hardness, the so-called Mohs scale, named after the German mineralogist Friedrich Mohs, who proposed his test method in 1811. Please indicate the correct statements in your opinion.
Glazed ceramic tiles are relatively hard, and scratches affect the aesthetic properties of the cladding, while also damaging its functional qualities.
The Mohs scale (mineralogical hardness scale) is a set of reference minerals for determining relative hardness using the scratching method. 10 minerals, arranged in order of increasing hardness, were taken as standards.
The Mohs scale is a method of rough comparative assessment of the hardness of materials according to the “harder - softer” system, where the material being tested is scratched by a reference mineral and its surface hardness on the Mohs scale is lower, or it is scratched by a reference mineral and its hardness is higher. Thus, the values of the Mohs scale can be considered indicators of the absolute hardness of minerals.
Mohs scale - determined by which of ten standard minerals scratches the material being tested, and which of ten standard minerals scratches the material being tested.
Unglazed ceramic tiles are relatively hard, and scratches only affect the aesthetic properties of the cladding, without damaging its functional qualities.
Material on this issue is presented in the article Surface hardness .
The quality and value of the cladding directly depend on the symmetry and uniformity of its individual components, i.e. individual tiles in relation to the quality of the surface and its dimensions. That is why, any dimensional differences and asymmetries of the tiles, deviations of the surface from flatness, which violate the harmony of the cladding and worsen its appearance, will be considered defects. The quality of the surface is determined by the presence of the following defects: gaps, cracks, lack of glaze, unevenness, depressions, pits, damage to the vitrified surface, specks and stains, body defects, decorative defects, darkening, chipped edges and corners.
The difference in size and dimensional deviations are expressed as a percentage of the working size of the tile.
The following type characteristics are important: length of the sides and thickness, straightness of the sides, orthogonality, flatness of the surface.
The method for controlling size and appearance characteristics is described in EN ISO 10545-2. To control the appearance, a minimum of 30 samples of tiles are selected, which must form a surface area of at least 1 m². The appearance of the tiles is checked visually (with the naked eye) at an illumination of 300 lux from a distance of 1 m from the observer’s eyes. According to the standard, preparation of the sample surface and visual assessment of the surface are carried out by different persons. Surface quality is expressed as a percentage of the number of tiles without defects.
If defective tiles do not exceed 5%, then the batch is assigned FIRST GRADE, and if they exceed 5%, then the batch is assigned SECOND GRADE.
The appearance characteristics, as well as the dimensional characteristics, are checked randomly on the tiles before they are packaged. Control is carried out visually by specially trained personnel (MANUAL SORTING) or by machine (AUTOMATIC SORTING).
Information on this issue is presented in the article Dimensional and type characteristics .
Water absorption is a parameter that determines the porosity of ceramic tiles. It is measured by the amount of water that ceramic tiles absorb under certain laboratory conditions, and is expressed as a percentage of the dry weight of the tiles.
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According to EN ISO 10545-3, the penetration of water into the open pores of samples is determined using two methods: boiling and water saturation in a vacuum. When boiling, water saturation occurs only in easily filled open pores; with the vacuum method, almost all open pores are filled.
According to EN ISO 10545-3, the penetration of water into the open pores of samples is determined exclusively using the water saturation method in a vacuum. The boiling method, as a test that does not allow determining open porosity and bulk density, is considered obsolete.
A low water absorption coefficient indicates that the structure of the tile is porous, and a high coefficient indicates that the structure of the material is more dense.
The lower the degree of water absorption, the more resistant the tile will be to intense mechanical and hydrothermal influences.
According to the EN 14411 standard, ceramic tiles and slabs are divided into three main groups based on water absorption. Where the third group corresponds to the lowest water absorption rates.
Material on this issue is presented in the article Water absorption .
Frost resistance - the ability of ceramic tiles to withstand freezing in a humid environment and at temperatures below 0 degrees Celsius. The freezing mechanism is divided into two stages. The first stage is the penetration of water from the environment into the pores of the tile. The second stage is the hardening (freezing) of water inside the pores. As is known, the transition of water from a liquid to a solid state is accompanied by an increase in volume, since the density of ice is less than the density of water. Thus, when water freezes inside the pores, the tile is subjected to mechanical stress, which can lead to cracks or chipping of part of the material.
According to EN ISO 10545-12:1997, tests confirming frost resistance properties are carried out as follows: ceramic tiles or slabs, after being saturated with water, are subjected to alternate temperatures of +5 ° C and minus 5 ° C. They are then completely frozen for at least 100 freeze-thaw cycles. After 100 freeze/thaw cycles, the faces and edges of ceramic tiles or slabs are examined for damage.
Frost resistance also prevents ice from forming on the face of the tile. This is due to the fact that water, without getting inside the material through the pores of the top layer, seems to “roll off” from the surface.
The frost resistance property of ceramic tiles is not guaranteed in extremely low temperature zones (below -40 °C). This is due to the test conditions of EN ISO 10545-12:1997, as they are carried out at temperatures between +5°C and -5°C. In this regard, manufacturers mark materials suitable for use in such an environment with a special EXTRA°C sign, which in turn indicates testing in the temperature range from -50 °C to +100 °C.
According to EN ISO 10545-12:1997, tests confirming frost resistance properties are not carried out as such. A material is considered frost-resistant if it falls into group 1 of materials according to the degree of water absorption (<3%).
Based on the mechanisms described above, the frost resistance of a material is determined by two parameters: 1) The presence and number of pores that allow water to penetrate into the material; 2) The shape and size of the pores, the volume of voids of which, allows you to distribute the loads of the changing state of water. It follows from this that frost resistance is directly related to water absorption: the lower the water absorption, the greater the likelihood that the material is frost-resistant. However, there are also highly porous materials (with a high rate of water absorption) that are characterized by frost resistance. Frost resistance in this case is due to the shape and size of the pores, allowing moisture to penetrate into the material without destroying it as a result of hydrothermal loads.
Based on the mechanisms described above, the frost resistance of a material is determined by the possibility of water penetration into the material, in other words, the degree of water absorption. Thus, if a material does not absorb water, it is frost-resistant, but if it does, it is not.
Material on this issue is presented in the article Frost resistance .
Thermal conductivity is the ability of material bodies to transfer energy (heat exchange) from more heated parts of the body to less heated parts of the body, carried out by chaotically moving particles of the body (atoms, molecules, electrons, etc.). Such heat exchange can occur in any body with a non-uniform temperature distribution, but the mechanism of heat transfer will depend on the state of aggregation of the substance. Porcelain stoneware, due to its dense, almost non-porous structure, is distinguished by relatively high thermal conductivity.
The thermal conductivity of ceramic tiles usually varies from 0.5 to 1.1 W/(m °C); lower values apply to porous materials (single and double fired tiles, monoporosity).
Porcelain stoneware, due to its dense, almost non-porous structure, has a relatively high thermal conductivity, which is higher than that of some other flooring materials (for example, natural stones such as marble or granite).
The thermal conductivity of ceramic tiles usually varies from 0.5 to 0.9 kcal/(m h °C); lower values apply to porous materials (single and double fired tiles, monoporosity).
The thermal conductivity of the flooring material becomes particularly important when the choice is made in favor of heated floors (warm screed). Here, naturally, porcelain stoneware with its high thermal conductivity has no competitors.
The SI unit for thermal conductivity is W/(m K).
The method for determining the thermal conductivity of ceramic tiles is given in ISO 10545-03. The essence of the method is that in steady state, the energy flux density transmitted through thermal conductivity is proportional to the temperature gradient.
Information on this issue is presented in the article Thermal conductivity .
