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.
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.
Glazed ceramic tiles are relatively hard, and scratches affect the aesthetic properties of the cladding, while also damaging its functional qualities.
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.
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.
Material on this issue is presented in the article Surface hardness .
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 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 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).
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.
The SI unit for thermal conductivity is W/(m K).
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).
Information on this issue is presented in the article Thermal conductivity .
Slip resistance is determined by the kinetic and dynamic conditions of motion of the body interacting with the surface. When it comes to flooring, it is obvious how the degree of slip is related to the safety of using the surface. Knowledge of surface properties is essential for the cladding designer, tiler, retailer and end user, as well as the safety inspector. Please mark the correct conclusions in your opinion:
Friction coefficient is a parameter characterizing the degree of surface sliding. It is proportional to the force parallel to the interaction surface that must be applied in order to create relative motion between two bodies. The higher its characteristics such as smoothness and shine, the lower the coefficient of friction for floor surfaces, since this contributes to the appearance of a thin, continuous layer of water (as well as grease, dirt, etc.), which acts as a lubricant between the sole and the floor. Ceramic tiles, while smooth and shiny, create a slippery surface and increase the risk of falls and accidents.
The DIN 51130 and DIN 51097 methods, also called "incline plane methods", consist of a person walking back and forth on a platform covered with the tiles being tested. The inclination of the test section increases at a constant rate until an angle is reached at which the person begins to feel unsure when walking, that is, begins to slide.
According to the DIN 51097 method, in rooms where floors are often wet and where people walk on them barefoot (for example, swimming pool sides, children's pools, common shower rooms, saunas, etc.), the classification contains groups: A; B (A+B); C (A+B+C). Where A is the slipperiest tile.
Ceramic tiles, characterized by their smoothness and shine, form the most intimate contact between the surface and the sole, thereby increasing the coefficient of friction. While rough, uneven surfaces tend to allow water or other liquids to accumulate on them, as well as dirt, grease and other substances that act as lubricants. In addition, the area of contact with the sole, in this case, is limited by the protruding edges of the surface, which also reduces slip resistance. This factor must be taken into account when choosing tiles.
According to the DIN 51130 method, floors in production facilities or work areas where there is a high risk of slipping are classified into the following groups (according to the average inclination angle): NC; R9; R10; R11; R12; R13. Where R13 is the slipperiest tile.
Material on this issue is presented in the article Slip resistance on dry and wet surfaces .
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.
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).
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.
The following type characteristics are important: length of the sides and thickness, straightness of the sides, orthogonality, flatness of the surface.
Information on this issue is presented in the article Dimensional and type characteristics .
The term craquelure itself refers to the crevices and cracks that form on the surface of the glaze. The pattern of these cracks is often circular, although they may be scattered across the surface of the glaze. The reason for the appearance of craquelure is either a difference in the coefficient of thermal expansion of the shard and the glaze, or deformation of the tile due to the impact of mechanical load on it.
“Late craquelure” occurs under the influence of the external environment during operation. The reasons for its appearance are: thermal shock, insufficient drying of the cement base, excessive cement content in the layer, excessive thickness of the mortar layer.
The test method for determining the resistance to cracking of glazes (craquelure) of ceramic tiles and slabs is given in the EN ISO 10545-18 standard. To determine the resistance to cracking of glazes, tiles and slabs are subjected to high pressure steam in an autoclave. Then the tiles and slabs, after applying the dye to the glazed surfaces, are examined for the presence of cracks in the glaze.
Glazed tiles with an "immediate crackle effect" are not considered defective, although manufacturers sometimes deliberately create collections of tiles with a "craquelure effect" for aesthetic purposes.
When craquelure appears on polished ceramic tiles and slabs, the term "polished craquelure" is used.
This defect can appear immediately after the end of the production cycle (in this case they speak of “immediate craquelure”) or some time after laying the tiles (in this case they speak of “late craquelure”).
The material on this issue is presented in the article “ Resistance to craquelure ” and “ Cracking of craquelure glaze ”.
