WO2023119341A1

WO2023119341A1 - Hardening composition, corresponding preparation method, and method to treat stone material

Info

Publication number: WO2023119341A1
Application number: PCT/IT2022/050338
Authority: WO
Inventors: Marcello SOLITO; Stefano Fioratti
Original assignee: Tenax S.P.A.
Priority date: 2021-12-21
Filing date: 2022-12-21
Publication date: 2023-06-29
Also published as: IT202100032036A1

Abstract

The liquid hardening composition, for treating stone material, is of the bi¬ component type and comprises a liquid resin and a hardening compound suitable to react with the liquid resin to form a solid polymer matrix. The invention also concerns a method to prepare the liquid hardening composition and a method to treat stone material.

Description

HARDENING COMPOSITION, CORRESPONDING PREPARATION METHOD, AND METHOD TO TREAT STONE MATERIAL

FIELD OF THE INVENTION

Embodiments described here concern a liquid hardening composition, usable for example for treating stone material, in particular of a light color or white, with the purpose of impregnating, gluing, reinforcing material and/or for filling holes, cracks or fissures and/or to glue and repair broken pieces of stone material.

BACKGROUND OF THE INVENTION

Resin-based compositions are known, for treating the rough surfaces of stone material, in particular for stone material intended for use in the decoration or furnishing of external or internal spaces, generally with the purpose of impregnating, gluing, reinforcing material and/or for filling holes, cracks or fissures. The known compositions can also be used for gluing and repairing broken pieces of stone material.

Given the intended use of the stone material, it must have perfectly flat surfaces, generally free from defects, even more so when the stone material is of a precious type such as marble.

The marble slabs that come out of quarries, despite the treatments and cutting performed in the quarries, very often have defects in their surfaces, in particular cracks or fissures, or even sometimes breaks. These damaged marble slabs cannot be used for decoration or furnishings and a treatment step is required, with a composition as indicated above.

The same type of problem is also found with stone material other than marble.

The known hardening compositions are generally of the bi-component type, with a liquid resin to which a hardening compound is added, suitable to react with the resin so as to induce its polymerization and thus make it solid. The resin and the hardening compound are both in liquid form, so that they can be applied homogeneously on the stone material and can fill the holes, cracks or fissures to be rectified, in order to obtain a perfectly smooth surface.

Hardening is allowed by the polymeric nature of the compounds based on which the resins are prepared. Depending on the nature of the polymeric compounds used, different hardening mechanisms and, therefore, different triggers of the hardening reaction are involved. For example, the hardening reaction can be triggered by exposure to UV light (photocatalysis) or by exposure to heat (thermal catalysis).

One disadvantage of the known hardening compositions is that they are transparent both in the liquid state and also after the hardening reaction. Therefore, the defects in the treated stone material remain visible, even if they are filled with resin. This defect is particularly noticeable when the stone material is light in color or white.

In an attempt to solve this problem, solutions have already been devised, such as for example adding micronized inorganic pigments to the hardening compositions, which are not soluble in them. But one problem encountered with pigments lies in their physical sizes, which do not allow them to go deep into the micro-holes and micro-cracks; the pigment remains suspended on the stone surface without going into depth. The result is that the defects in the stone material are filled with a hardened resin having practically two distinguishable colors, which does not allow the defects to be masked effectively.

Hardening compositions have also been devised in which a liquid dye has been added to the composition, so as to make the latter colored already in the liquid state. However, it has been found that the hardening step causes the formation of a precipitate of the dye inside the resin. This results in a hardened resin with a colored precipitate in a transparent matrix, which suffers from the same problems as resins with micronized pigments and therefore does not meet the needs of this sector.

CN-A- 104231844 describes a coating powder containing epoxy resin, a hardening agent, polyester resin, benzoin, micro wax powder, cellulose acetate butyrate and a pigment. The coating powder is used to give a glossy effect, and is not intended or suitable for coating stone material. Cellulose acetate butyrate is not used as a dye, and is present in a proportion of less than 0.1% by weight of the total weight of the coating powder.

There is therefore a need to perfect a liquid hardening composition which can overcome at least one of the disadvantages of the state of the art.

To do this, it is necessary to solve the technical problem of providing a liquid hardening composition which, once hardened, allows to effectively mask the defects that can be found on the surfaces of stone material. One purpose of the present invention is to provide a liquid hardening composition which has the same color or a color very close to the color of the stone material treated, after it has been hardened.

Another purpose of the present invention is to provide a transparent and liquid hardening composition which, once applied and hardened on the stone surface to be treated, has a uniform color throughout the volume occupied, even at the bottom of holes, cracks and/or fissures.

Yet another purpose of the present invention is to perfect a method to prepare a liquid hardening composition which can be used to effectively mask the defects which can be found on the surfaces of stone material.

A further purpose is to devise a method to treat stone material which allows to effectively mask the defects which can be found on the surfaces of stone material.

The Applicant has devised, tested and embodied the present invention to overcome the shortcomings of the state of the art and to obtain these and other purposes and advantages.

SUMMARY OF THE INVENTION

The present invention is set forth and characterized in the independent claims. The dependent claims describe other characteristics of the present invention or variants to the main inventive idea.

In accordance with the above purposes, and to resolve the technical problem disclosed above in a new and original way, also achieving considerable advantages compared to the state of the prior art, a hardening composition according to the present invention for treating stone material is in liquid form and comprises a resin, a hardening compound and a coloring compound. At least the resin is in liquid form and preferably transparent. The hardening compound is suitable to react with the resin to form a solid polymer matrix. Preferably, the hardening compound is also in liquid form and preferably transparent.

The coloring compound, on the other hand, is in the form of a powder or liquid, obviously colored, white or black depending on the stone material to be treated. Naturally, the coloring compound becomes transparent once dissolved in the resin. The hardening compound is of the type that is soluble in the resin and/or in the hardening compound when these are in the liquid state, but it is not soluble in the solid polymer matrix which is formed by the reaction between the resin and the hardening compound. This causes the coloring compound to crystallize again when the hardening composition hardens, causing the hardened resin to become colored.

According to some embodiments, the coloring compound reacts with radiation of a predefined wavelength and/or with heat, to change color. For example, the coloring compound can react with UV rays, in particular UV-A, UV-B, UV-C and UV-V rays, or through exposure to microwaves, macrowaves or infrared radiation.

In particular, the coloring compound is selected from cellulose derivatives. Preferably, the coloring compound is selected from cellulose acetates. More preferably, the coloring compound is selected from cellulose diacetate, cellulose acetate propionate, cellulose acetate butyrate and their mixtures. Even more preferably, the coloring compound is selected from cellulose diacetate and cellulose acetate propionate, possibly mixed with cellulose acetate butyrate.

Advantageously, the coloring compound is present at a concentration higher than 0.1% by weight of the total weight of the composition, preferably higher than 0.2%, more preferably higher than 0.5% by weight of the total weight of the composition. Preferably, the coloring compound is present at a concentration lower than 10% by weight of the total weight of the composition, preferably lower than 5% by weight of the total weight of the composition.

In accordance with one aspect, a method is provided to prepare a hardening composition for treating stone material, in particular a hardening composition as indicated above.

The preparation method provides to prearrange a resin in liquid form, a hardening compound suitable to react with the resin to form a solid polymer matrix and a coloring compound in the form of a powder, wherein the coloring compound is soluble in the liquid resin and/or in the hardening compound but it is not soluble with the solid polymer matrix. The method subsequently comprises a step of dissolving the coloring compound in the resin and/or in the hardening compound. In particular, the dissolving step occurs under stirring and advantageously at a heated temperature.

According to one aspect, a method is also provided to treat stone material in which a hardening composition is used, in particular a hardening composition as indicated above.

The treatment method provides to prearrange a composition comprising a resin in liquid form, a hardening compound suitable to react with the liquid resin to form a solid polymer matrix and a coloring compound dissolved in the resin and/or in the hardening compound, and mix the resin with the hardening compound. After this step, a mixture in liquid form and preferably transparent is obtained. The treatment method subsequently provides a step of applying the liquid mixture obtained on a stone material, and a step of hardening the same mixture.

The hardening step preferably provides a step of catalysis of a polymerization reaction between the resin and the hardening compound. The hardening step can be initiated by heating and/or exposure to radiation, for example UV radiation, in particular UV-A, UV-B, UV-C and UV-V, or by exposure to microwaves, macrowaves or infrared radiation.

Advantageously, the coloring compound is sensitive to radiations of a predefined wavelength and/or to heat, and the hardening step involves a change of color of the coloring compound.

In one variant, the treatment method provides to reciprocally glue two pieces of stone material by means of the liquid hardening composition. In particular, the mixture obtained after having mixed the resin and the hardening compound is applied on a respective surface of each of the two pieces, these surfaces being put into reciprocal contact before the step of hardening the liquid mixture.

In accordance with another aspect, a use of a hardening composition in liquid form and comprising a resin, a hardening compound and a coloring compound is provided, wherein the coloring compound is instead in the form of a powder or liquid, and of the type that is soluble in the resin and/or in the hardening compound when these are in the liquid state, but not soluble in the solid polymer matrix which is formed by the reaction between the resin and the hardening compound, for treating stone material. Preferably, the hardening composition is as indicated above.

DESCRIPTION OF SOME EMBODIMENTS

Unless otherwise defined, all the technical and scientific terms used here and hereafter have the same meaning as commonly understood by a person with ordinary experience in the field of the art to which the present invention belongs. Even if methods and materials similar or equivalent to those described here can be used in practice and in the trials of the present invention, the methods and materials are described hereafter as an example. In the event of conflict, the present application shall prevail, including its definitions. The materials, methods and examples have a purely illustrative purpose and shall not be understood restrictively.

All measurements are carried out at 25 °C (ambient temperature) and at atmospheric pressure, unless otherwise indicated. All temperatures are in degrees Celsius, unless otherwise indicated.

All percentages and ratios indicated shall be understood to refer to the weight of the total composition (w/w), unless otherwise indicated.

All percentage ranges indicated here are given with the provision that the sum with respect the overall composition is 100%, unless otherwise indicated.

All the intervals reported here shall be understood to include the extremes, including those that report an interval “between” two values, unless otherwise indicated.

The present description also includes the intervals that derive from uniting or overlapping two or more intervals described, unless otherwise indicated.

The present description also includes the intervals that can derive from the combination of two or more values taken at different points, unless otherwise indicated.

By water, distilled water is meant, unless otherwise specified.

Proportions are stated in phr units, which stands for “parts per hundred resin”, commonly used to express quantities of additives to be added to a resin. In the context of the present application, phr corresponds to the weight in grams of a certain compound to be added to 100 grams of resin, and is therefore equivalent to a percentage by weight of the weight of the resin.

According to the present invention, a hardening composition, in particular for treating stone material, is of the bi-component type and comprises a resin and a hardening component to be added to the resin for its hardening. Obviously, the hardening compound is suitable to react with the resin in such a way as to cause its polymerization, which results in a solid polymer matrix.

The resin can be of a known type, in particular it can be an epoxy resin or a polyester resin, possibly modified, for example with diluents, or it can be of the so-called accelerated or pre-accelerated type. By epoxy resin it is advantageously meant standard liquid epoxy resins from bis-phenol-A and bis-phenol-F, with EEW of 180-190 and viscosity between 3000- 15000 cps at 25°C. It is also possible to use epoxy resins from bis-phenol-A and bis-phenol-F with EEW higher or lower than 180-190, use lower viscosity or even higher viscosity epoxy resins until they become solid or semi-solid resins with average molecular weights Mw that are lower than 700 g/mol, between 700 and 1000 g/mol, and higher than 1000 g/mol. It is also conveniently meant all epoxy derivatives referred to as reactive plasticizers and/or reactive diluents with 1, 2, 3, 4, 5, 6, 7, 8 epoxy functions. It is also possible to use resins called epoxy-phenolic and epoxy-novolac with one or more functionalities. All resins, polymers, oligomers, monomers and/or substances which contain reactive epoxy rings (oxirane ring) are included.

Polyester resins are advantageously based on unsaturated polyester dissolved in reactive monomers, and they are preferably selected from orthophthalic, isophthalic, neopentyl, dicyclopentadiene resins, vinyl ester resins, epoxy acrylic resins and acrylic resins.

These unsaturated polymers are suitably dissolved in reactive monomers, among which, for example, styrene is the most common. Or other vinyl, acrylic and meta-acrylic unsaturated type monomers with one or more functionalities. For example: 1,4 butanediol diacrylate, HDDA, DPGDA, TMPTA, MMA, alphamethyl styrene, vinyltoluene.

The hardening compound can be an amine, in particular selected from monoamines, diamines and triamines. Amines can be both cycloaliphatic, aliphatic and also aromatic containing primary, secondary and tertiary hydrogens. More preferably, the hardening compound is a diamine, for example 1,3- bis(aminomethyl)cyclohexane 1,3BAC. The hardening compound can also be selected from thiols and mercaptans with primary and secondary hydrogens. In the formulation of the hardening compound it is possible to use plasticizers and accelerators such as benzyl alcohol, nonylphenol, bis-phenol A, additives of various kinds to improve adhesion and resistance to atmospheric agents.

The hardening composition also comprises a coloring compound, the function of which is to give a color to the resin, in particular after it has been hardened due to its reaction with the hardening compound. The coloring compound is provided in the form of a powder or liquid. It is soluble in the resin, whether epoxy or polyester, and in the hardening compound when they are in their liquid form, so that when the composition is applied to the stone material to be treated it is in a liquid and transparent form, with the coloring compound distributed homogeneously in the composition. The liquid form of the composition allows the coloring compound to arrive even in spaces that do not allow the passage of micronized pigments.

It is also possible to provide coloring compounds in liquid form and/or based on any cellulose derivative whatsoever.

The same coloring compound, however, is not soluble in the solid polymer matrix which forms in the reaction between the resin and the hardening compound. Therefore, during the hardening of the composition, the coloring compound crystallizes again and is no longer integrated into the polymer matrix. In this way, the coloring compound is visible, giving its color to the hardened composition.

In addition, the coloring compound can also be primed, for example by means of the same priming that triggers the hardening reaction between the resin and the hardening compound, so as to give its own color to the composition, or to change color, according to requirements. For example, the coloring compound can be sensitive to light, in particular to UV rays such as for example UV-A, UV-B, UV- C and/or UV-V rays. In this case, exposure of the coloring compound to UV rays causes a change in its color, from transparent to colored, or from a first color to a second color. The coloring compound can also be sensitive to other types of priming, such as heat, microwave, macrowave or infrared radiation by means of electric or gas IR radiation lamps, for example.

The coloring compound is chosen from monosaccharides and all their derivatives, such as polysaccharides with molecular weight of any type. It is also possible to use polymers/plastics of the synthetic type, such as polystyrene, polymethylmethacrylate, polycarbonate, inorganic metal salts and organo-metallic compounds, for example.

The coloring compound is favorably selected from cellulose diacetate polymers, cellulose acetate propionate polymers, cellulose acetate butyrate polymers and mixtures thereof. It is also possible to use starch and starch derivatives. Natural polymers based on chitosan or chitin and their derivatives are also provided. The cellulose diacetate, cellulose acetate propionate and cellulose acetate butyrate polymers mentioned above are white in color and are therefore particularly suitable for application on white or very light-colored stone material, such as marble for example.

A method to prepare the composition provides to make available a resin and a hardening compound as described above, both in liquid form and preferably transparent. A coloring compound is also made available in the form of a powder to be dissolved in the resin and/or in the hardening compound.

A step of dissolving the coloring compound in the resin and/or in the hardening compound follows. The dissolving step is generally performed under heating and/or stirring.

Once the coloring compound has dissolved, the composition can be preserved, in suitable conditioning, for further use, or it can be used instantly to treat stone material.

This treatment of the stone material provides a step of mixing the resin and the hardening compound, with the coloring compound dissolved in at least one of the two. At the end of this step, a transparent liquid mixture is obtained which is ready to be applied on the stone material, for example spread or sprayed.

During this step of applying the liquid mixture, this latter is to be applied in such a way as to fill the defects found, such as holes, cracks or fissures, and then spread to obtain a surface that is as smooth as possible. Please note that it is also possible to apply the liquid mixture on two separate pieces, for example following a break, in order to assemble them.

Subsequently, there is a step of hardening the liquid mixture, in particular through catalysis of the reaction that occurs between the resin and the hardening compound, and which forms the solid polymer matrix. It is observed that only the resin and the hardening compound react in this step, the coloring compound does not react and returns to its solid powder form, and therefore colored. The crystallization of the coloring compound gives color to the hardened composition.

In the case of a UV-sensitive coloring compound, exposure of the composition to UV rays results in a color change of the coloring compound which causes the composition to color in a predefined color, which can be the same color as the initial powder form of the coloring compound, or a different color. The hardening step can be performed in a known manner, in particular by applying heat, by exposure to light with a predefined wavelength, for example ultraviolet light, microwave or macrowave radiation systems, radiation with electric or gas IR lamps, or simply leaving the mixture at ambient temperature.

EXAMPLE 1

The hardening composition comprises an epoxy resin modified with a C12-C14 type epoxy diluent and an IPDA diamine-based hardening compound also containing benzyl alcohol at a dosage of 30 phr.

The coloring compound comprises cellulose diacetate, cellulose acetate propionate and cellulose acetate butyrate and comes in the form of a white powder. The coloring compound is hot dissolved into the epoxy resin at a concentration of 4% wt:wt by weight of the resin. The dissolution is performed at 80°C by mixing with a Cowless impeller. A solution of resin with dissolved coloring compound of a transparent color is obtained.

The hardener is added to the resin thus prepared, mixing them in order to obtain a homogeneous mixture. The mixture obtained is spread on a slab of white Carrara marble. When freshly applied to the marble, the mixture is still transparent.

The slab is then put in a static oven at 50°C for 3 hours. Upon leaving the oven, the composition is visibly of a white color. The appearance of the color is more evident when the thickness of the mixture applied is greater.

A step of finishing the slab follows, in which it is wet polished with a sequence of abrasives of common use for the person of skill in the art. Looking at the finished slab, the filled cracks and holes are colored in white with a natural effect reminiscent of crystal.

EXAMPLE 2

The hardening composition comprises an orthophthalic polyester resin dissolved in styrene to which an amine is added as an accelerator. Subsequently, cellulose diacetate, cellulose acetate propionate and cellulose acetate butyrate are dissolved therein at 50°C under stirring with a Cowless impeller for 2 hours. The resin thus prepared is left to rest for one night at ambient temperature. Thus a transparent resin is obtained.

The hardening compound is benzoyl peroxide based, in the form of a paste. The paste is added to the resin at a concentration of 2-3% by weight of the total weight of the mixture obtained.

The mixture obtained is used to glue two pieces of Greek Thassos marble together. Also in this example, the mixture freshly applied on the marble surfaces to be glued together is transparent.

The hardening step is performed at ambient temperature. As it gradually hardens, the composition turns white and increasingly blends in with the two pieces of glued marble.

EXAMPLE 3

The hardening composition comprises an epoxy resin to which there have been added an acrylate diluent TMPTA and a hardening compound based on 1,3-BAC diamine and benzyl alcohol dosed at 25 phr. This type of composition is particularly suitable for the resin treatment of very porous white marble slabs.

The coloring compound comprises cellulose diacetate, cellulose acetate propionate and cellulose acetate butyrate in the form of a white powder. This coloring compound is hot dissolved in the epoxy resin at a concentration of 2.5% by weight of the weight of the resin, at 80°C by mixing with a Cowless impeller. The resin thus prepared is transparent.

The hardening compound is added to this resin, mixing to obtain a homogeneous mixture. The mixture obtained is then spread on a slab of white Greek Pirgos marble. The freshly applied mixture is still transparent.

The slab is then put in a static oven at 40°C for 2 hours and 30 minutes, for the hardening step.

After the hardening step, the spread mixture has turned white, this effect being more evident when the thickness of the applied mixture is greater. The slab is finished by wet polishing with a sequence of abrasives of common use for the person of skill in the art. The defects found before the treatment are now grouted and white in color with a natural crystal-like effect.

EXAMPLE 4

In this example, the hardening composition is of the bi-component type thixotropized with pyrogenic silica. This type of product is generally used for grouting and repairing natural stone. The addition of pyrogenic silica allows to obtain a product that does not drip or create drops, and therefore applicable vertically. The hardening composition comprises an epoxy resin to which there have been added an acrylic thinner, a hardening compound based on cycloaliphatic diamine (IPDA) and benzyl alcohol at 45 phr, and a coloring compound in the form of a white powder, comprising cellulose diacetate, cellulose acetate propionate and cellulose acetate butyrate.

The coloring compound is dissolved in the resin at a concentration of 2.5% by weight of the weight of the resin, the dissolution is carried out at 80°C under stirring with a Cowless impeller. A transparent resin is obtained. The resin thus prepared is cooled to 25-30°C and pyrogenic silica is added to it, in the form of a very fine powder, at 5% by weight. The pyrogenic silica is dispersed under vacuum for about 20 minutes using a mixer with central Cowless and lateral scraper. The paste thus obtained has an appearance reminiscent of ice, due to the pyrogenic silica.

A part of pyrogenic silica is added to the hardening compound following the same vacuum dispersion procedure described for the resin. The hardening compound thus prepared also has an ice-like appearance.

The resin and the hardening compound are mixed in the ratio resin:hardening compound equal to 2: 1, on the basis of stoichiometry calculations and on the basis of the percentage of pyrogenic silica.

The mixture thus obtained is applied on a Greek Volakas marble which usually has many defects such as fractures, holes and cracks on the surface to be polished.

The hardening step provides to let the marble, on which the mixture has been spread, rest outdoors at a temperature comprised between 20 and 25°C for 48 hours.

The defects found on the marble before applying the hardening composition are grouted and white in color, and blend well with the color of the marble. Also in this case the coloring effect is more evident when the applied thickness is greater.

The treated marble is then subjected to wet polishing with a sequence of abrasives well known to the person of skill in the art. The grouted defects are white with a natural crystal-like effect.

It is clear that modifications and/or additions of parts or steps may be made to the hardening composition, to the corresponding preparation method and to the method to treat stone material as described heretofore, without departing from the field and scope of the present invention, as defined by the claims.

It is also clear that, although the present invention has been described with reference to some specific examples, a person of skill in the art shall certainly be able to achieve many other equivalent forms of hardening composition, corresponding preparation method and method to treat stone material, having the characteristics as set forth in the claims and hence all coming within the field of protection defined thereby.

Claims

1. Liquid hardening composition for treating stone material, comprising a liquid resin and a hardening compound suitable to react with said liquid resin to form a solid polymer matrix, characterized in that it also comprises a coloring compound in the form of a powder or liquid selected from cellulose derivatives, said coloring compound being soluble in said liquid hardening composition but not soluble in said solid polymer matrix.

2. Hardening composition as in claim 1, characterized in that said coloring compound is sensitive to radiation of a predefined wavelength and/or to heat, and changes color when exposed to them.

3. Hardening composition as in claim 1 or 2, characterized in that said coloring compound is selected from cellulose acetates.

4. Hardening composition as in claim 3, characterized in that said coloring compound is selected from cellulose diacetate, cellulose acetate propionate, cellulose acetate butyrate and their mixtures.

5. Hardening composition as in any claim hereinbefore, characterized in that said coloring compound is dissolved in said resin and/or in said hardening compound.

6. Hardening composition as in any claim hereinbefore, characterized in that said coloring compound is present at a concentration higher than 0.1% by weight of the total weight of the composition.

7. Hardening composition as in any claim hereinbefore, characterized in that said coloring compound is present at a concentration lower than 10% by weight of the total weight of the composition.

8. Method to prepare a liquid hardening composition for treating stone material, characterized in that it comprises the subsequent steps of prearranging a liquid resin, a hardening compound suitable to react with said liquid resin to form a solid polymer matrix, and a coloring compound in the form of a powder or liquid selected from cellulose derivatives, said coloring compound being soluble in said liquid hardening composition but not soluble in said solid polymer matrix; and dissolving said coloring compound in said liquid resin and/or in said hardening compound.

9. Preparation method as in claim 8, characterized in that said coloring compound is selected from cellulose acetates, preferably from cellulose diacetate, cellulose acetate propionate, cellulose acetate butyrate and their mixtures.

10. Method to treat stone material, characterized in that it comprises the steps of prearranging a liquid hardening composition comprising a liquid resin, a hardening compound suitable to react with said liquid resin to form a solid polymer matrix, and a coloring compound selected from cellulose derivatives and dissolved in said resin and/or in said hardening compound, said coloring compound being soluble in said liquid hardening composition but not soluble in said solid polymer matrix; mixing said resin and said hardening compound to obtain a liquid mixture; applying said liquid mixture on said stone material; and making said mixture harden to form said solid polymer matrix.

11. Method to treat stone material as in claim 10, characterized in that said step of making said liquid mixture harden provides a catalysis of a polymerization reaction between said resin and said hardening compound by means of exposure to heat and/or to radiation of a predefined wavelength.

12. Method to treat stone material as in claim 11, characterized in that said coloring compound is sensitive to radiation of a predefined wavelength and/or to heat, and in that said step of making said liquid mixture harden involves a change of color of said coloring compound.

13. Method to treat stone material as in claim 10, 11 or 12, characterized in that said stone material comprises two separate pieces to be glued, and in that said liquid mixture is applied on respective surfaces of each of said pieces to be glued, and said surfaces are put into reciprocal contact before the step of hardening said liquid mixture.

14. Use of a hardening composition as in any claim from 1 to 7 to treat stone material.