EP1183219A1

EP1183219A1 - Method of treating ceramic materials and natural minerals and use of quartz and silicate-like material in the method

Info

Publication number: EP1183219A1
Application number: EP00914211A
Authority: EP
Inventors: Veijo Kaipainen; Seija Ollila
Original assignee: No-Pintatekniikka Oy
Current assignee: No-Pintatekniikka Oy
Priority date: 1999-03-25
Filing date: 2000-03-24
Publication date: 2002-03-06
Also published as: WO2000058236A1; AU3561500A

Abstract

A method is disclosed for strengthening and/or sealing ceramic materials and natural minerals. The invention is characterized in that the method is carried out substantially impregnating a composition containing quartz and silicate-like solids into the substrate material, most advantageously into the pores, crystalline grain borders and cracks thereof.

Description

Method of treating ceramic materials and natural minerals and use of quartz and silicate-like material in the method

The present invention relates to a method for strengthening and/or sealing ceramic materials and natural minerals. The invention further relates to the use of quartz and a silicate-like solids in the method.

In the literature, ceramic mateπals are generally categorized as compositions formed from metal oxides and silicates. This definition is very broad and, accordingly, ceramic compositions are known in the art in plural variations (including glasses). The properties of a ceramic material are not determined by the components of its composition alone, but rather the same components can be the starting materials of different compositions depending on the values of kinetic and temperature-related variables during the formation of the composition.

The bonding mechanism in the silicon dioxide elementary unit and the formation of the Si tetrahedron, as well as the tendency of the tetrahedrons to undergo a complex polymerization into chains, planes and lattice structures are the basic concepts that must be elaborated to understand the structures of ceramic compositions and glass formation, as well as material properties of ceramic materials.

The partially ionic or covalent nature of bonds in a silicon dioxide material determine its physical-chemical properties, wherein a covalent bond is substantially stronger than an ionic bond.

Covalent bonds in silicate glass are the basis of its polymerized structure. If other substances are added to the lattice structure of the Si tetrahedrons, they may disrupt or modify the lattice (modifying agents) or bond with the lattice structure so as to modify only the material properties. Na, Ca and Fe ions are all capable of affecting the stability of the Si tetrahedron lattice structure so as to allow these ions to change the material properties. The change of basic material properties is different depending on whether the ions form bridges between the tetrahedrons or whether the modifying effect is simply caused by the bonding of ions to the lattice structure through disruption of the covalent bonds of the structure. The structure formations in, e.g., quartz, tridymite and cristobalite are based on the different variations of the same tetrahedral scheme. Herein, the tetrahedrons may be connected to each other by different angles thus forming varying lattice structures.

Due to the above-described reasons, the formation of a glass-like material is not dependent on the components alone that are selected for the preparation of the composition, but rather, the molecular structure (lattice) determines the glass properties. Si, Ti, Ge, N, and other elements may act as the glass- forming atoms, the overwhelmingly most common being Si. The Si-O bond is may be characterized as about 50 % ionic and by 50 % covalent. Normally, elements capable of forming a lattice have at least about 50 % ionic character. Hence, silicon dioxide and different silicates can form a variety of different glasses. Also the different additives modify glass properties. Herein, addition of Na ions disrupts the lattice, see FIG. 1. The Ca ions act as typical bridging elements that are bonded to the lattice by two oxygen bonds. The bonding is affected by the size of the ions. As the foreign ions cause a change in the bond angles of the tetrahedral lattice, the lattice properties are modified, whereby the lattice structure can accommodate tetrahedrons by a varying density so that, e.g., the lattice may become less dense (by Na addition) or denser (by Ca addition), see FIG. 2.

In an Na₂0*Si0₂-Si0₂ system, the lattice structure over the entire molar ratio scale is glass-like, see FIGS. 3 and 4. The Si0₂ system may form different lattice structures known as quartz, cristobalite and tridymite. These structures have different molar ratios of Na ions. Quartz occurring as a natural mineral is a very hard material. In this type of so-called acid glass, the Na ion can have an inhibitory effect, e.g., on fungal growth and bacterial metabolism when the ion embedded in a ceramic structure.

Conventional window glass compositions comprise the system CaO-Na₂0- Si0₂. As the Ca ion acts as a bridging element in the system, its higher content in the composition increases the ionic nature of the system.

When the amount of calcium addition becomes significantly high, granular material begins to form in the glass. While still within the glass-like region, the addition of Ca ions hardens the glass, but the increase of hardness also leads to loss of toughness. In this region, the material becomes brittle and breaks at the Ca-O bonds. Resultingly, the material is durable only under unstressed conditions.

Silicates are typical glass formers. The number of different glasses has been estimated at about 600. Glass may occur in a stable state also in a structure resembling an undercooled liquid, wherein Si atoms are assumed to be arranged in a tetrahedral-like configuration but having a nonorganized order in the bonding of the tetrahedrons with each other, because the kinetic cooling dynamics have not given the structure enough time to assume a fully ordered lattice configuration.

In the art, the term glass is defined to refer to a transparent material, whereby the word glass itself does not reveal the materials included in the composition or its properties.

Glass-like materials must thus be understood to be composed as a combination of oxide and silicate lattices resulting in a very complex structure. Hence, the exact background of glass formation phenomena in ceramic materials is very difficult to explain in theoretical terms. In practice, the glass-like skeleton formed by the tetrahedral lattice structure of silicates is the backbone of hardness in ceramic materials. Glass-like materials and coatings are charac- terized by brittle breaking under a blow. Breaking takes place along the crystalline grain borders of the oxide inclusions of the silicate skeleton. In addition to its glass-like skeleton, a ceramic material also contains separate oxide components that form the softer, nonglassy portion of the material having a tinted or white colour. Ceramic materials, typically those of the man- made variety, are characterized by a high content of pores. Also a natural material is porous, but yet denser than pottery or concrete, for instance. Due to its inherent permeability to water, a ceramic material generally needs some type of coating treatment: glazing, gel-coating, painting, silicate compound application and the like. Glaze may be applied by melting, silane treatment, growth from an aqueous solution, etc. Aqueous solutions have also been used as paint additives. Traditionally, the goal has been to achieve a water- resistant coating.

A repairing posttreatment of a glaze has not normally been carried out as the means thereto have been lacking.

A glass-like coating is advantageous, because the silicate lattice adheres to the substrate material in a natural manner via chemical bonds and its lacera- tion has not been a similar problem as that occurring in a separately applied coating made using a noncompatible material. Glaze makes porous ceramics water-resistant and gives good protection against corrosion.

Depending on the application, ceramic materials have been coated by glaze layers of different types and thicknesses. Walls do not generally require a thick coating, while horizontal surfaces such as floors are more demanding. Thereon, the coating must endure varying blows and imposed pressures. Also the corners and edges of wall surfaces are subject to forces imposed by the inherent weight of the material and stresses from thermal expansion.

One of the greatest problems occurring in glass-like glazes is caused by cracks and crevices due to the hardness of the glaze. Therefrom active calcium oxide can leak through that then gathers dirt and is difficult to clean away. This spoils the good properties of the glass-like glaze. The glaze layer loses its water resistance and allows the surface-active material diffusing into a crack to develop a chemical corrosion center, whereby the CaO tends to leak out and adhere to the outer surface of the glaze. The surface also becomes pervious to different liquids.

Furthermore, the joints between ceramic tiles are porous as well as subject to break down under abrasion, and they gather dirt. As the water-impervious glaze does not "breathe" so that gaseous substances could escape through the tile, the rear of the tile cannot dry up thus supporting fungal growth.

When the glaze cracks, the ceramic substrate material can absorb different liquids such as oils, acids from foodstuffs, aqueous solutions, etc., that are difficult to clean away. This may be one of the reasons why glazes are not renewed. Bacteria and microorganisms can pass through the joints and cracks thus making worn surfaces and joints unhygienic.

EU directives have posed new requirements in terms of, e.g., hygienics, a problem that is aggravated in hospitals by contaminants. A further problem hampering the use of ceramic materials has been their tendency to crack due to their structure which prevents their use under conditions specified for good resistance to pressure and impact loads. The same applies to ceramic coatings, too.

In summary to the above-mentioned it will be appreciated that a glass-like glaze is a good choice in terms of water resistance and corrosion protection as long as it remains intact. Problems arise from damage to the glaze. The glaze breaks due to its brittle nature thus being weak under mechanical wear, pressure and impact loads. The major problems herein are traced to the filtration of calcium salts through the structure and the activity (hydrolyzation) of the calcium salts, as well as from the soaking of the structure by different liquids.

Glazes are made by a heat treatment process (melting), hardening a silicate frit, silane treatment and deposition from an aqueous sol. Aqueous sols have also been used as binders in paint systems. The use of aqueous sols is based on the capability of silicates and oxides to hydrolyze thus being capable of becoming incorporated in a lattice structure when the sol is dried.

On vertical surfaces (such as walls), a thin glaze is often sufficient. Ceilings are coated by different compounds. Floor surfaces need a thick glazing (on tiles), whereby the joints remain more problematic. The requirements posed on utensils and articles vary depending on whether the objects are used as decoration or as cooking utensils (enameled kettles), glasses, cups, pots, etc. In addition to water resistance, some of the objects are also expected to have good durability under temperature changes. Hence, the selection of a glaze is combined with the selection of ceramic materials from a group of alternatives of widely varying porosities.

Patent publication EP 0 952 127 A1 discloses a method in which a thin glass- like surface film is deposited from an aqueous solution. The aqueous solution is used in the same manner as a glazing paint to form the thin glass-like film on vertical surfaces of a building material. On porous substrates, the surface must be treated 5 times to form a nonporous film on the substrate surface. The method is proposed for forming a coating on the walls of a swimming pool. Obviously, the method is not applicable to the treatment of horizontal surfaces.

The strength of a glass-like glaze in structures subjected to mechanical stress is weaker at the edges and corners, because these areas are loaded by the inherent weight of the structural material and stresses imposed by thermal expansion. As glassy film cannot act as a reinforcing structure, water resistance cannot be assured at these points. Hence, leaks in swimming pools as well as at wall joints of humid spaces are a common problem, and so is also fungal growth in the foundations of buildings. A solution to the problem has been sought from additional dressing of the grouted joint, but dressing compounds are porous and have a short life under a prolonged stress.

It is an object of the present invention to provide an entirely novel method capable of strengthening and/or sealing ceramic materials and natural minerals so that the above-mentioned problems are eliminated. Simultaneously, the method according to the invention offers improved protection to the substrate material against bacterial attack and other similar factors causing hygienic problems. The goal of the invention is achieved by way of utilizing a novel approach in which impregnation is used in lieu of a conventional surface treatment. More specifically, the method according to the invention is characterized in that strengthening and/or sealing steps in the method are carried out principally by virtue of impregnating quartz and silicate-like solids into the substrate material, most advantageously into the pores, crystalline grain borders and cracks thereof.

The present invention is characterized by strengthening and sealing of ceramic materials and natural minerals by virtue of impregnating an aqueous quartz-silicate composition into the pores, crystalline grain borders and cracks of the substrate material.

As known from the prior art, the water resistance of ceramic materials has been sought from the use of various coatings. The selection of such coatings is determined by the application. If the objective is not set as to form a continuous watertight film or coating on the substrate material, but rather, to modify the inherent properties of the substrate material by way of, e.g., sealing the material structure, a number of benefits are gained over coatings.

The inherent water-wicking property of a ceramic material can be utilized if the impregnation thereof with an aqueous solution is allowed to transport quartz and silicate-like solids into the structure of the material. These solids will settle in an inhomogeneous manner into the pores, crystalline grain borders and cracks thus fortifying the material and blocking filtration of calcium salts through the structural matrix of the material. If the inherent water wicking capability of the substrate material is high, a portion of its pores can be filled with commercially available microspheres that due to their larger particle size (d = about 1 mm) are superior in filling the pores. To prevent the formation of a watertight film, the treated surface must be rinsed effectively with water to prevent a glass-like film from settling on the substrate surface.

If the composition of the impregnating solids is matched with that of the hardest component (quartz) in the ceramic substrate material, the hardness and durability of the treated ceramic substrate can be improved substantially. Then, a structure is obtained equivalent to natural stone materials that have a lower porosity. E.g., in concrete conventionally used as load-bearing floor surface under demanding conditions, quartz as an aggregate of the material gives the more strength the greater its relative proportion in the impregnant and the deeper the composition is impregnated. In comparison, the inherent water absorption capability of concrete is quite high.

If the impregnating solids are complemented with Na silicate as an aqueous solution, generally known as water glass, this so-called acid glass improves the hygienic nature of the material in three different ways. Firstly, the sodium acts as an acidic element inhibiting fungal growth and occurrence of bacteria. Secondly, the reduced porosity prevents the material from being soaked with such liquids (water and other liquids) that can promote fungal growth and bacterial metabolism. Thirdly, as the system avoids the formation of an entirely sealing film, the material capability of "breathing" is not lost thus permitting natural drying of the material.

The need for sealing depends on the water absorption capability of the sub- strate material. If the material is inherently impervious or has been glazed on its surface, its water absorption rate is so slow that a separate treatment is needed for improving the absorption rate. A diluted aqueous solution of ammonium bifluoride can be used for etching the structure of a glaze. This so-called pore-opening treatment is a precondition for the posttreatment of materials already put in use.

In a renovation treatment such as made on, e.g., soiled floors having calcium salts already diffused onto its surface, the area must be cleaned prior to the pore-opening treatment. Acetic acid and hydrochloric acid may be used for dissolving the oxides of the substrate material, thus allowing the surface to be both made porous for its softer components and cleaned free from different contaminants, a part of which may be organic by nature. The cleaning operation can be performed using commercial detergents, but they are not always effective in dissolving calcium salts that have already diffused onto the substrate surface.

If a ceramic material or natural mineral is used under humid conditions, e.g., in saunas and shower rooms, the floor surface is advantageously given an antislip treatment. Conventionally, this has been carried out by an acid treatment using hydrochloric acid, for instance. The goal of the antislip treatment is to make the substrate surface microscopically rough to increase the coefficient of friction and prevent water from forming a slippery film. This goal is more advantageously attained using a glass-etching compound, whereby the antislip effect is gained with much milder etching than by using hydrochloric acid, for instance. This technique is based on etching the microcracks of the material surface that have a sharper and more durable structure.

One disadvantage of a glazed surface is its slipperiness. In contrast, if the material is sealed using the above-described method, its surface will not become as slippery as a glazed surface, whereby the antislip treatment is not needed over the entire floor surface. Moreover, when the antislip treatment of the floor is performed by etching the glass-like coating, its tendency to accumulate soil is reduced from that achievable by way of an antislip treatment performed by etching the softer components of the material.

The overall durability of a material treated by the present method becomes much more resistant to washing cycles so that the material can be cleaned without damage using pressurized water jet washers. The treatment is particularly advantageous on floor surfaces having the tile joints treated by the impregnant. Initially, the thick glaze of the tiles can take the pressurized water jet washing but not so the joints. Additionally, the present treatment makes the tile material more durable than it was originally. The attained strength is determined by the depth to which the impregnation is or can be performed, this being dependent on the outcome of the substrate surface etching.

The substrate material need not be treated by its full depth in all cases, particularly not when the strength specifications are less demanding. Herein, the required depth of treatment is determined by the following factors: amount of solids in the aqueous treatment solution, duration of impregnation, duration of pore-opening treatment, drying temperature, effectiveness of cleaning and inherent water wicking capability of substrate material, and the amount of micropheres possibly used.

The method according to the invention is advantageously carried out in four steps:

1) cleaning the surface using an appropriate acid treatment

2) opening the substrate pore structure by etching

3) impregnating

4) performing the antislip treatment.

Depending on the application, the material is subjected to the necessary steps of the above-given four-step list. Acid solutions with the substances dissolved therein are removed by vacuum suction after the completion of each treatment step. The surface is rinsed with abundant water and allowed to dry between the successive treatment steps. After the impregnation step, the substrate material is allowed to dry for 24 h prior to being subjected to loads.

The acids (acetic acid, hydrochloric acid, other necessary solvents) are used in a concentration as diluted as possible so that the acid concentration at the most soiled areas is increased as required. The acid is allowed to work for a few minutes and the surface is rubbed with a squeegee or mop. Respectively, the concentration of the ammonium bifluoride solution is kept as low as possible. The working time of the applied fluoride solution is determined by the degree of surface roughness and user's experience. The treatment agents are applied directly to the surface to be treated.

The impregnation step is carried out in the same fashion as described above, but now the time allowed for impregnation is substantially longer when a nonporous or glazed material is to be treated. After the impregnation step, the surface must be rinsed carefully to clean the surface free from the impregnation composition.

The method is particularly suited for treating essentially horizontal surfaces. Treatment of entirely vertical surfaces is rather difficult by virtue of the method, since aqueous solutions tend to fall away along the surface and the time for impregnation remains short. Porous materials having a good water wicking capability can be treated in a satisfactory manner.

In the following, the invention will be described in greater detail with the help of a few preferred exemplifying embodiments.

Example 1 Cleaning and repair treatment of ceramic tile surfaces of a swimming pool and its sanitary spaces.

1) Cleaning

CH₃COOH, acetic acid, pH 4.7, HCI, hydrochloric acid, pH 4.7 or CH₃COOH + HCI, pH 4.7

First cleaning, then vacuuming the liquid away and finally rinsing with abundant water. The surface is allowed to dry.

2) Opening the pores

Distilled water + ammonium bifluoride, pH 6.0 (acetic acid may be added, pH adjusted)

First spreading the liquid, then allowing to work for about 5 min. The surface roughness is verified. Finally vacuuming the liquid away and rinsing with abundant water.

3) Impregnating

30 g/l milled Na₂0^»Si0₂-Si0₂ powder mixed in distilled water (80 % Si0₂ by weight)

Spreading the liquid on the floor so that all areas are copiously covered, then allowing to work for 10 min. Rinsing the floor with abundant water over all areas and allowing to dry for 24 h.

4) Antislip treating, for surfaces under traffic/motion or soaked with soapy liquids

Ammonium bifluoride solution, pH 4.9

Spreading thinly on the floor and allowing to work for about 1 min. Vacuuming the liquid away and rinsing with abundant water.

Example 2

Treatment of floors of sanitary spaces or halls in a hospital, foodstuff industry plant or the like when the final result is desired to be improved hygienics and the load-bearing capability requirements of the floor are not demanding.

Treatment is performed as in Example 1 without the antislip treatment step. In the sealing composition, the amount of NaO is 35 %, whereby the amount of Si0₂ will be 65 %. (It must be noted that the acid nature rendered by NaO inhibits microorganism cultures, whereby its proportion may even be increased.)

Example 3

Treatment of a porous, unglazed clay pot.

3) Impregnating

35 g/l milled Na₂0^«Si0₂-Si0₂ powder mixed in distilled water (65 % Si0₂ by weight)

10 g/l microspheres

The liquid is impregnated into the inner surface by allowing the liquid to stay in the pot. Rinsing and drying as above. The pot may be surface-treated (painting, glazing) after thorough drying. Example 4

Strengthening treatment of a concrete floor required to have a good mechani- cal resistance to wear (imposed by, e.g., cars or machines continuously moving on the floor).

A new floor needs no cleaning. Renovation treatment in old premises requires precleaning with an aqueous solution of acetic acid and hydrochloric acid (pH 4.7) until contaminants (oil residues) have been removed by the acid treatment.

3) Impregnating

35 g/l milled Na₂OSiθ2-Si0₂ powder mixed in distilled water (95 % Si0₂ by weight)

The liquid is impregnated into the concrete for, e.g., 15 min (depending on the local circumstances) and is allowed to dry for 24 h.

Due to its porosity, concrete will absorb large volumes of the liquid without any pore-opening treatment. In the case that the requirements for the final result are very demanding, also the pore-opening step may be included.

Through modifying the appropriate treatments described in above examples, a plurality of different materials can be treated, e.g.:

Grouting concrete (requires use of microspheres in the treatment), marble (advantageously using the ammonium bifluoride treatment), bricks, soapstone and the like ceramic/porous materials.

The amount of quartz in the quartz-silicate composition used in the method according to the invention is adjusted according to the material to be treated and/or the final properties required therefrom. Hence, the proportion of quartz to be used in the quartz-silicate composition varies according to the particular application, especially according to the desired strength, whereby the quartz percentage in the composition may rise up to almost 100 %, advantageously up to 50 - 95 %, particularly advantageously up to 60 - 75 %. To improve the hygienic and antibacterial properties, sodium oxide may be added to the quartz-silicate composition by an amount rising up to 50 %, while advantageously an amount of 20 - 30 % is used.

In the method, the impregnation depth of the quartz-silicate composition in the substrate material to be impregnated is determined by the intended application and requirements specified for the substrate material. In most cases, the impregnation depth is selected based on empirical data. Hence, the depth to which the substrate must be impregnated varies starting from an essential surface strengthening and/or sealing of the material being treated to full-depth impregnation of the entire substrate material. In other words, the goal is to adjust the depth of the impregnation treatment with the quartz- silicate composition such that an essential strengthening and/or sealing effect is attained. While any fixed limits are difficult to define, an advantageous impregnation depth is 5 - 95 %, preferredly 10 - 70 %, of the total thickness of the substrate material. The essential feature of the invention is that composition is impregnated into the substrate material.

In accordance with the above-discussed, the treatment compositions include Na silicates and quartz, but in principle the filling of the substrate material pores is not limited to any particular selection of the solids used herein, whereby also other glass-like components can be added to the water- or solvent-based composition. Of conventional glass-like materials, quartz has the highest hardness and is the most cost-effective choice when the treatment is specified to improve the substrate material hardness. The treatment has a very slight tinting effect on the substrate material colour as the glass-like filler component has a different coefficient of refraction. Optionally, when the final product is desired to become coloured, the treatment composition may be complemented with colour-rendering oxides as additives.

It must be noted further that the surface texture of the treated substrate itself does not change in the impregnation treatment, because the surface itself is not primarily subjected to any treatment.

To those skilled in the art, it is obvious that the invention is not limited to the above-described exemplifying embodiments, but rather, may be modified within the scope of the appended claims. In addition to swimming pools, the premises in which the invention may be practiced include industrial spaces, hospitals, sports activity halls, foodstuff industry premises, exterior wall surfaces, brick walls and washing and shower spaces needing the sealing of building structures. Furthermore, the method can be applied for protecting objects such as marble surfaces, decoration and statues against decay, improving the wear resistance of, e.g., marble tile floors and treating surfaces in concrete-walled basins and the like. More generally, the method is suited for improving the properties of porous materials mentioned in the above description of the invention by virtue of impregnating solids into the substrate material matrix.

Claims

What is claimed is:

1. Method for strengthening and/or sealing ceramic materials and natural minerals, characterized in that the strengthening and/or sealing steps of the method are carried out substantially by impregnating quartz and silicate-like solids into the substrate material, most advantageously into the pores, crystalline grain borders and cracks thereof.

2. Method according to claim 1, characterized in that the method particularly utilizes the water absorption capability of a ceramic material through impregnating quartz and silicate-like solids in the form of a quartz- silicate composition into the substrate material.

3. Method according to claim 1 or 2, characterized in that in the method, for the purpose of improving the effect of the impregnation treatment, the substrate surface is cleaned prior to the impregnation step, advantageously using an acid treatment, and subsequently the substrate surface is subjected when necessary to a pore-opening treatment step performed by etching.

4. Method according to any one of claims 1 -3, characterized in that in the method the impregnation step is followed when necessary by an antislip treatment of the substrate surface.

5. Method according to claim 3 or 4, characterized in that the pore- opening step and/or the antislip treatment step are most advantageously performed using ammonium bifluoride in the treatment.

6. Method according to any one of claims 1 -5, characterized in that the lattice structure of the silicate-like component may contain different atoms such as Si, Ti, Ge, N as required by the application, most advantageously the component consisting of sodium silicate.

7. Method according to any one of claims 1 -6, characterized in that the proportion of quartz in the quartz-silicate composition used in method is selected according to the substrate material being treated and/or the properties to be given to the material.

8. Method according to claim 7, characterized in that the proportion of quartz in the quartz-silicate composition used in method varies according to specific needs, particularly according to the hardness desired from the treated substrate material, whereby said proportion in the composition may rise up to almost 100 %, advantageously up to 50 - 95 %, particularly advantageously up to 60 - 75 %.

9. Method according to any one of claims 1 -8, characterized in that, to improve the hygienic and antibacterial properties, the quartz-silicate composition may contain sodium oxide by an amount rising up to 50 %, most advantageously being in the range of 20 - 30 %.

10. Method according to any one of claims 1 -9, characterized in that the impregnation depth of the quartz-silicate composition in the substrate material to be impregnated is determined by the intended application and requirements specified for the substrate material.

11. Method according to claim 10, characterized in that the depth to which the substrate is impregnated varies starting from an essential surface strengthening and/or sealing of the substrate material being treated and at the maximum extending to full-depth impregnation of the entire substrate material.

12. Method according to claim 10 or 11, characterized in that the depth of the impregnation treatment with the quartz-silicate composition is adjusted according to the properties of the material being treated such that an essential strengthening and/or sealing effect is attained, whereby an advantageous impregnation depth is 5 - 95 %, most advantageously 10 - 70 %, of the total thickness of the substrate material.

13. Use of quartz and silicate-like solids for strengthening and/or sealing ceramic materials and natural minerals by virtue of impregnating said solids into the substrate material, most advantageously into the pores, crystalline grain borders and cracks thereof.

14. Use according to claim 13, in which particularly the water wicking capability of said ceramic material is utilized for impregnating quartz and silicatelike solids in the form of a quartz-silicate composition into the substrate material matrix.

15. Use according to claim 13 or 14, wherein improved hygienic and antibacterial properties are gained by adding when required sodium oxide in the treatment composition.