Stain resistance of ceramic tiles refers to their ability to withstand aggressive chemical agents. Such chemical agents may contain components that, when interacting with the tile, can corrode the surface or penetrate inside and change the appearance of the surface.
Harsh chemicals, acids or bases, can be found in various processed liquids (e.g. milk in dairies, grease and oil in garages, blood in slaughterhouses, laboratory chemicals), in various products that may come into contact with lined surfaces (e.g. food, ink, etc.), as well as in cleaning products used to clean and care for the surface.
Deterioration in the appearance of the lined surface may be due to the following mechanisms of action of various chemical agents:
- Firstly, a real chemical reaction between the chemical and the tile, which entails changes in the tiled surface (in principle, all ceramic surfaces are quite resistant to chemical influences, with the exception of hydrofluoric acid);
- Secondly, absorption. In this case, the chemicals penetrate into the tiles and remain there, not necessarily forever, and although it is possible to remove them, they are, however, quite difficult.
Such mechanisms explain why often (see article Abrasion resistance, wear resistance ) indicators of resistance to chemical attack are much lower on surfaces subject to intense abrasive loads, causing the microporosity of ceramic tiles. The combination of mechanical and chemical effects causes significant visible damage to the tile, deteriorating the quality of its surface.
Test methods for determining the stain resistance of facing surfaces of ceramic tiles and slabs are given in EN ISO 10545-14:1997 , IDT. The stain resistance of ceramic tiles or slabs is determined by exposing the surface of the ceramic tiles or slabs to test solutions and materials for an appropriate period of time. After this, the surface of the ceramic tiles or slabs is cleaned in the prescribed manner and examined for visible changes. If it is necessary to test the surfaces of tiles or slabs that are not covered with glaze, then the samples are prepared according to the requirements of EN ISO 10545-7 at 600 revolutions. According to test results, depending on the stain-forming agent, the tiles are divided into five classes (as the resistance decreases): Class 1; Class 2; Class 3; Class 4; Class 5.
Test methods for determining the chemical resistance of ceramic tiles and slabs at room temperature are given in EN ISO 10545-13:1997 , IDT. The samples are exposed to the test solutions, and after a specified period of time, the destruction is visually determined. This method applies to all types of ceramic tiles and slabs.
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Stain resistance
EN ISO 10545-14 Determination of stain resistance.
Cleaning methods:
- Method A. The test samples are cleaned under running hot water for 5 minutes, after which their surface is wiped with a damp cloth;
- Method B. Test samples are manually cleaned with a mild cleaning agent using non-scratch natural sponges or wipes. After this, their surface is washed under running water and wiped with a damp cloth;
- Method C. The test samples are cleaned mechanically using strong cleaning agents: a rotating brush with a diameter of 8 cm with stiff bristles at a rotation speed of 500 rpm; container for cleaning agent with appropriate supply, connected to the brush. Cleaning is carried out for 2 minutes, after which the surface is washed under running water and wiped with a damp cloth;
- Method D. The test samples are immersed in an appropriate solvent for 24 hours, after which the surface is thoroughly washed under running water and wiped with a damp cloth. Cleaning is considered complete after removing the stain with one of the solvents;
Stages of stain removal. The test samples are cleaned using one of the methods indicated above (method A, B, C or D).
Classification based on test results. Based on the test results, the surfaces of the tested samples are divided into five classes: Class 1; Class 2; Class 3; Class 4; Class 5. The test results for each sample using each of the specified stain formers (with or without a wear test on unglazed ceramic tiles or slabs) are recorded. Class 5 corresponds to the easiest level of stain cleaning; Class 1 means that the stain cannot be cleaned by any of the specified methods and/or indicates the presence of irreversible damage to the front surface.
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Determination of chemical resistance
EN ISO 10545-13:1997 recommends the following aqueous test solutions:
4.1 Household chemicals .
Ammonium chloride solution, 100 g/l. 4.2 Bath salts .
Sodium hypochlorite solution, 20 mg/l, prepared from commercially pure sodium hypochlorite with 13% (m/m) active chloride. 4.3 Acids and alkalis .
4.3.1 Low concentrations (L):
a) hydrochloric acid solution, 3% (V/V), prepared from concentrated hydrochloric acid (1.19 g/ml);
b) citric acid solution, 100 g/l;
c) potassium hydroxide solution, 30 g/l.
4.3.2 High concentrations (H)
a) hydrochloric acid solution, 18% (V/V), prepared from concentrated hydrochloric acid (1.19 g/ml);
b) lactic acid solution, 5% (V/V);
c) potassium hydroxide solution, 100 g/l.
Unglazed ceramic tiles or slabs are classified into the following classes.
7.2.1 For test solutions according to 4.1 and 4.2:
- class UA: no visible changes;
— class UВ: visible changes on cut surfaces;
- class UC: visible changes on the cut surfaces, on the edge of the sample, which is the edge of a tile or slab, and on the front side.
7.2.2 For test solutions according to 4.3.1:
- ULA class: no visible changes;
— ULV class: visible changes on cut surfaces;
- ULC class: visible changes on the cut surfaces, on the edge of the sample, which is the edge of the tile or slab, and on the front side.
7.2.3 For test solutions in accordance with 4.3.2:
- class UNA: no visible changes;
— class UNB: visible changes on cut surfaces;
- class UNC: visible changes on the cut surfaces, on the edge of the sample, which is the edge of a tile or slab, and on the front side.
Glazed ceramic tiles or slabs are classified into the following classes.
8.2.3.1 For the test solutions specified in 4.1 and 4.2:
- class GA(V): no visible change;
— class GB(V): significant changes in appearance;
— class GC(V): partial or complete loss of the original surface.
8.2.3.2 For test solutions specified in 4.3.1:
- class GLA(V): no visible change;
— class GLV(V): significant changes in appearance;
— class GLC(V): partial or complete loss of the original surface.
8.2.3.3 For test solutions specified in 4.3.2:
- class GHA(V): no visible changes;
— class GНВ(V): significant changes in appearance;
— class GHC(V): partial or complete loss of the original surface.
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