EP4284765A1

EP4284765A1 - Binding paste and mix for making a flooring

Info

Publication number: EP4284765A1
Application number: EP22704579.6A
Authority: EP
Inventors: Alberto Ferrari
Original assignee: Ferrari Granulati Srl
Current assignee: Ferrari Granulati Srl
Priority date: 2021-01-27
Filing date: 2022-01-26
Publication date: 2023-12-06
Also published as: IT202100001646A1; WO2022162548A1

Abstract

A binding paste (12) for making a flooring (10) is a mixture which comprises a fluid substance and a powdered substance. The binding paste (12) has a volumic mass value which is greater than or equal to 2500 kg/m3. A mix for making the flooring (10) comprises pieces of a solid material (11) and a binding paste (12) which is a mixture comprising a fluid substance and a powdered substance. The binding paste (12) has a density which is greater than the volumic mass of the solid material (11). Specifically, the powdered substance in the binding paste is powder of at least one material which has a volumic mass value greater than or equal to 3800 kg/m3. For example, the powdered substance is powder of at least one material selected from the following materials: aluminium oxide or alumina; barium sulphate or barite; zirconium silicate; zirconium oxide or zirconia; titanium dioxide; rutile; chromite; magnetite. For example, the fluid substance in the binding paste is water and the binding paste also comprises a cementitious binding substance, or the fluid substance is a polymeric substance such as a resin. For example, the pieces of the solid material (11) are pieces of at least one material selected from the following materials: quartz; glass; marble; granite; porphyry. The flooring (10), which in particular is a flooring of the Venetian type, is formed by a layer of solidified binding paste in which the pieces of the solid material (11) are embedded and bound by the solidified binding paste.

Description

BINDING PASTE AND MIX FOR MAKING A FLOORING

★ * *

DESCRIPTION

This invention relates in general to the construction sector and in particular relates to making flooring. Specifically, the subject matter of this invention can be applied for making flooring of the "Venetian" type (also known as “Venetian terrazzo flooring"), formed by a layer - generally poured in place - in which pieces of inert solid material are embedded and bound by a solidified binding paste. The inert solid material, which is usually a stone material, is selected with the desired characteristics in terms of colour, veining, size and other aesthetic aspects.

Flooring of this type is considered high quality and is very much in demand on the market, both for residential buildings and commercial buildings. Making it professionally requires highly qualified workers, who are difficult to find in Italy, despite its centuries-old culture in this type of flooring, and who are even more difficult to find abroad.

The prior-art technique used to make a Venetian flooring consists of spreading on a floor screed, professionally prepared, a mix composed of a binder (liquid mortar, cement mixed with marble powder or quartz sand, or resin) and of pieces of an inert solid material. The layer of mix, which is spread with a thickness of around 20 - 40 mm, is left to harden for the time necessary. After the layer of mix has hardened, finishing is performed, that is to say, removal of the surface part of the layer by multiple processing passes (roughing, grinding, polishing). In general, from 3 to 6 mm of the thickness of the layer should be removed, so as to show the pieces of inert solid material which are surrounded by the binder.

However, depending how the pieces of solid material are distributed in the thickness of the layer, it may be necessary to remove much more binding paste (that is to say, a greater thickness) before reaching the pieces of solid material and revealing them.

Moreover it may be the case (and often is) that the surface after grinding still has more or less large zones in which only the binder is visible and not the pieces of solid material, since these remained lower in the layer. In practice, the surface does not have a reasonably even distribution of the pieces of solid material and conversely it has patches of binder, which have a negative aesthetic impact.

In order to overcome the aesthetic disadvantage due to such patches it is necessary to further grind the entire surface to reach the pieces of solid material even at the patches, or to grind only where the patches are present. The first case involves not just an increase in the processing time and the labour required, but also a lowering of the height of the entire flooring, with the risk of creating unwanted steps at door sills. The second case involves creating localised hollows which are definitely unsightly.

Attempts to facilitate laying of this type of flooring have been in progress for a long time, trying to make up for the lack of qualified workers. At least some of these attempts involved trying to make the mix more fluid, so as to allow laying and levelling of the layer of mix which is easier and faster, as well as being performable with good results even by workers without special qualifications. Specifically, self-levelling systems were proposed. However, a more fluid mix is generally obtained by increasing the fluidity of the binder or by increasing the quantity of binder while the quantity of pieces of solid material remains the same.

That increases the above-mentioned disadvantages relative to the thickness of the layer to be removed and the presence of patches of binder. Consequently it is necessary to spread a layer of mix with a thickness greater than the usual one, in order to be able to remove more of it if necessary, thereby increasing material consumption, grinding waste produced, labour and the cost in general.

Other methods were also proposed although they do not fall within the proper definition of "Venetian flooring". For example, Canadian patent application CA 955,382 A proposed making a decorative flooring by fixing fragments of solid material on a surface to be floored, then filling the spaces between the fragments of solid material with a mortar containing hydraulic cement; obviously it is not a flooring formed by a layer poured in place, since the solid material is positioned before the cementitious mortar is added. It should also be noticed that the mortars proposed in CA 955,382 A have densities similar to or less than the densities of the prior-art binding pastes which are used to make Venetian flooring. International patent application WO 97/27982 A1 describes a method for making slabs or blocks of cementitious material comprising a granulated material of natural stone and a cementitious matrix for filling the spaces between the granulated material. Therefore, as for CA 955,382 A, document WO 97/27982 A1 does not relate to a flooring formed by a poured-in-place layer and it should also be noticed that the cementitious matrices mentioned in it have densities similar to or less than the densities of the prior-art binding pastes which are used to make Venetian flooring.

In this context, the technical purpose which forms the basis of this invention is to provide a solution for making a flooring of the type mentioned, such that it allows the above- mentioned disadvantages of the prior art to be overcome or at least offers an alternative to the currently known solutions.

The technical purpose and the aims specified are substantially achieved by a binding paste according to claim 1 , by a mix according to claim 3, by a method according to claim 14, by a use according to claim 15. As will be made clearer below, these subjects of the invention relate to different viewpoints of the invention and share the same inventive concept relative to the prior art, therefore we believe that unity of invention is met for them.

Particular embodiments of this invention are defined in the corresponding dependent claims.

This invention begins with the observation, by the Inventor, that the above-mentioned disadvantages with reference to the prior art are linked to the fact that the pieces of inert solid material tend to sink in the binding paste, due to their density which is greater than the density of the binding paste.

The inert solid materials used in the prior art have a density of around 2500 - 2900 kg/m³. The binding paste used in the prior art is composed for example of cement, marble powder and water, or of resin and marble powder. The marble powder has a density of around 2500 - 2800 kg/m³ and the cement has a density comparable to that value, but in any case the total density of the binding paste is much lower due to the necessary presence of the water (density of 1000 kg/m³) or of the resin (density of around 1100 kg/m³). For example, a binding paste containing white cement 22% by volume, marble powder 50% by volume, water 28% by volume has a density of around 2300 kg/m³.

Therefore, in the layer of mix which is spread when making the flooring, the pieces of inert solid material tend to settle on the bottom (often in a non-homogeneous way) because they have a density greater than the binding paste (still fluid) in which they are located, whilst the binding paste tends to rise to the surface. The viscosity of the binding paste opposes the tendency of the pieces of solid material to fall downwards, therefore in the solidified layer the pieces of solid material can be found throughout the entire thickness. However, it is a tendency which has an effect on the distribution of the pieces of solid material and leads to the above-mentioned disadvantages.

Moreover the more fluid mixes used to facilitate laying accentuate the disadvantages because, having a lower viscosity, they allow greater mobility of the pieces of solid material towards the bottom.

Having identified and understood these aspects, the Inventor devised the solution of a binding paste having a density greater than the density of the solid material of which the pieces are made.

In a mix which uses that binding paste, the pieces of solid material tend to float and therefore in the layer of mix they tend to go to the surface rather than settling on the bottom.

That allows several advantages over the prior art.

First, since the pieces of solid material tend to be positioned at the surface, the surface of the layer laid can have aesthetic uniformity and be without patches of binder even before starting the grinding operation.

Moreover, since the excess binding paste tends to settle on the bottom of the layer and the pieces of solid material tend to appear on the surface, a slight removal of the surface part of the layer is sufficient in order to reveal the pieces themselves in a satisfactory way during grinding. That is useful for reducing the processing times, labour, polishing waste and costs.

Furthermore, for the same reasons the layer of material which is spread can have a lower thickness than the thickness required for the prior art. Therefore, it is even possible to make savings in terms of material.

Finally, thanks to the fact that the starting point is a binding paste with a higher density than the prior art ones, it is possible to increase the fluidity and the smooth flowing of the mix as in the prior art attempts, but without that involving the above-mentioned disadvantages.

The Inventor carried out research and experiments to identify possible materials usable to make a binding paste with the required density.

According to one aspect of the solution proposed by the Inventor, the marble powder of the prior-art binding paste is at least partly substituted with powder of a material which has a density greater than or equal to 3800 kg/m³. Examples of suitable materials are: aluminium oxide (or alumina); barium sulphate (or barite); zirconium silicate; zirconium oxide (or zirconia); titanium dioxide; rutile; chromite; magnetite.

In this way it is possible to obtain a binding paste having a density of up to 3200 kg/m³ (or even higher), which is much greater than the density of the inert solid materials commonly used in the sector. According to another aspect of the solution proposed, the Inventor identified that a binding paste having a density which is greater than or equal to 2600 kg/m³ is suitable for the purpose. For some uses within the scope of the solution proposed, even a binding paste with a density of less than 2600 kg/m³ is suitable for the purpose; for example a binding paste with a density greater than or equal to 2500 kg/m³, in particular greater than or equal to 2550 kg/m³, is suitable for lighter inert solid materials such as some glasses. Some of the inert solid materials usable for the pieces (such as quartz, some glasses, some granites) have a density of around 2500 kg/m³ and therefore a binding paste with density greater than or equal to 2600 kg/m³ allows sinking of the pieces to be avoided or even promotes their "floating".

In the case of solid materials with lower density (for example other glasses), which may have a density of less than 2500 kg/m³, the above may also be achieved using a binding paste with density greater than or equal to 2500 kg/m³, in particular greater than or equal to 2550 kg/m³.

In the case of solid materials with higher density (heavy glasses, marbles, heavy granites, porphyries), which may have a density even of up to 2900 kg/m³, the use of a binding paste with density greater than or equal to 2600 kg/m³ (or possibly greater than or equal to 2500 kg/m³) is useful even if the binding paste has a density which is less than that of the solid material.

Indeed, even if the greatest advantages are obtained when the binding paste has a density greater than that of the solid material, a binding paste with density just less than that of the solid material (for example, at least 90% of the density of the solid material) reduces the sinking of the pieces of solid material compared with the prior-art binding pastes (which have a much lower density) and therefore can at least partly provide the advantages discussed.

According to another aspect of the invention, the composition of the binding paste (in terms of materials used and of quantities present) is selected based on the solid material of which the pieces are made, in such a way as to comply with a predetermined relationship between their densities. In particular, the powdered substance to be used in the binding paste and its quantity are selected in such a way that the density of the binding paste is greater than the density of the solid material of which the pieces are made. However, at least in some cases it may be sufficient for the density of the binding paste to be greater than or equal to 90% of the density of the solid material of which the pieces are made.

An inventive concept of this invention is the use of a binding paste with a higher density than the binding pastes used in the prior art, so that the density of the binding paste is near or even higher than the density of the material used for the pieces of solid material; in this way, sinking of the pieces of solid material in the binding paste is eliminated or at least reduced.

It should be noticed that, in this description, the term "density" is understood to mean "volumic mass”, that is to say, mass per unit of volume. The terms "density" and "volumic mass” are both used in this description, but it shall be understood that they refer to the same physical quantity.

Further features and the advantages of this invention will be more apparent in the detailed description of its example, non-limiting embodiments.

Reference will be made to the figures of the accompanying drawings, in which:

- Figure 1 shows an example of flooring made using a mix according to the prior art;

- Figure 2 shows an example of flooring made using a mix according to this invention;

- Figure 3 shows a perspective view of a sample which was made using a mix according to the prior art;

- Figure 4 shows a perspective view of two samples which were made using two different mixes according to this invention;

- Figure 5 shows, in a sectional view, the thickness of a sample made using another mix according to this invention;

- Figure 6 shows, in a simplified way, a portion of flooring according to this invention;

- Figure 7 shows, in a simplified way and not to scale, a transversal section of the portion of flooring of Figure 6.

With reference to what has already been discussed above, this invention can be applied for making a flooring which is formed by a layer in which pieces of a solid material are embedded and bound by a solidified binding paste. The pieces of solid material, which have dimensions of several millimetres or centimetres (for example, the largest dimension of the pieces is between 3 and 20 mm, in particular between 6 and 15 mm) and generally derive from crushing of stone material or of other inert material, remain visible on the surface of the flooring obtained and significantly contribute to the appearance of the flooring. A flooring of this type is well known as "Venetian flooring" or "Venetian terrazzo". According to one commonly used way of making it, a mix containing the binding paste and the pieces of solid material is prepared and then poured in place to form a layer. After the binding paste has solidified, the visible surface of the layer is ground in place and polished.

The binding paste used to prepare the mix is a mixture which comprises a fluid substance (for example water) and a powdered substance (for example cement and marble powder); the binding paste may be more or less fluid depending on requirements, in any case it must be fluid enough to obtain a mix which is pourable in place.

Figure 1 shows, for illustration purposes, a surface portion of a flooring 9 (more precisely, of a sample of flooring) which was obtained in accordance with a prior-art technique for making a Venetian flooring. The pieces of solid material 91 , having different dimensions and shapes, are visible on the surface and are surrounded by a matrix of solidified binding material 92, with a pale and homogeneous colour.

However, in Figure 1 it is easy to see how the distribution of the pieces of solid material

91 is not very homogeneous and how in particular there are quite large zones in which only the binding material 92 is present. Some of these zones, which effectively look like pale patches, are labelled with the reference number 93. The evident presence of such zones which are without pieces of solid material 91 ruins the appearance of the flooring 9 and constitutes a defect, which is more serious the larger and more numerous the zones are.

It should be noticed that Figure 1 relates to a mix which was spread with a thickness of 20 mm and from which 5 mm were then ground.

A sample 95 made by the Inventor according to the prior art is shown in Figure 3. The sample was made using pieces of solid material 91 which is marble and a binding paste

92 which is composed of white cement, marble powder, water and a water reducing additive (polycarboxylate ether powder (PCE), such as BASF Melflux 4930F). Therefore it is a binding paste 92 of the cementitious type with marble powder and is entirely similar to the binding pastes commonly used in the prior art.

The following table indicates the quantities used, the respective volumic masses, the percentage composition and the average volumic mass of the binding paste 92 obtained. Component Quantity Volumic Volume Mass Volume

(mass in mass (cm³) % % grams) (kg/m³)

White cement 50 3100 16.1 29.2 21.7

Marble powder 100 2700 37.0 58.5 50.0

Water 20 1000 20.0 11.7 27.0

Water red. additive 1 1000 1.0 0.6 1.3

TOTAL 171 2300 74 100 100

The binding paste 92 and the pieces of marble 91 were mixed together for the time necessary to obtain a well-mixed mix. The mix was put in a mould up to a height of 20 mm, which is approximately the minimum height for the layer which is normally spread to make a Venetian flooring. After solidification of the binding paste 92, the sample 95 was removed from the mould, was sectioned (the vertical face 96 is a sectional plane) and was partially ground on the top face 97.

Therefore, the sample 95 can be considered representative of a flooring obtained using a mix with the same composition. The vertical face 96 shows the height or thickness of the sample 95 and corresponds to a vertical section of the flooring.

The vertical face 96 shows that the pieces of marble 91 are not evenly distributed in the thickness of the sample 95 and have sunk towards the bottom of the sample 95, whilst the top of the sample 95 has an upper layer 98 which is almost exclusively formed by binding paste 92. The top face 97 of the sample 95 removed from the mould (the top face 97 would correspond to the surface of the flooring) shows only the binding paste 92. In order to reveal the pieces of marble 91 it is necessary to grind the top face 97 to remove all of the upper layer 98, as has partially been done on the sample 95.

Since the upper layer 98 has a thickness of several millimetres, in the case of a flooring its removal involves considerable labour and a lot of waste in the form of dusts and slurries from the grinding.

Moreover, the preferential distribution of the pieces of marble 91 towards the bottom and an incomplete removal of the upper layer 98 cause, on the surface of the flooring, the above-mentioned zones or patches 93 in which the pieces of marble 91 are substantially absent.

The table indicated above shows that the volumic mass (that is to say, the density) of the binding paste 92 is 2300 kg/m³. The volumic mass of the pieces of marble 91 is 2700 kg/m³. Since the pieces of marble 91 have a density greater than that of the binding paste 92 in which they are located, after the mix has been spread the pieces of marble 91 tend to sink and the binding paste tends to remain on the surface. The result is visible in the vertical face 96 of the sample 95.

In the prior art, a binding paste with a larger quantity of water to increase its fluidity is commonly used, which further reduces the volumic mass of the binding paste, or liquid mortar is used, which has a volumic mass of around 1900 - 2100 kg/m³.

Another prior-art binding paste is composed of fluid epoxy resin (25% by mass) and marble powder (75% by mass). Since the epoxy resin has a volumic mass of 1100 kg/m³, the volumic mass of the binding paste is less than 2000 kg/m³.

Considering the lower volumic mass, the use of such binding pastes as an alternative to that identified above makes the disadvantages mentioned even more serious.

All of these considerations, which were developed by the Inventor to identify the technical problem and to arrive at the invention, led the Inventor to identify the technical solution of using a binding paste with a higher volumic mass, which is close to or even higher than the volumic mass of the material used for the pieces of solid material.

That can be achieved by selecting a material with high volumic mass (in particular, with volumic mass greater than or equal to 3800 kg/m³) for the powdered substance in the binding paste, at least partly substituting the marble powder. The solution of using such a material for a binding paste to make a flooring is part of the invention.

Specifically, the powdered substance in the binding paste is powder of at least one material selected from the materials in the following table, which also indicates the volumic mass, the hardness on the Mohs scale and the type of colour.

Material for the powdered substance Volumic mass Hardness in the binding paste (kg/m³) (Mohs)

Pale colour (white /pale grey / beige)

Aluminium oxide or alumina 4000 9.0

Barium sulphate or barite 4400 3.0

Titanium dioxide 4200

Zirconium silicate 4700 7.5

Zirconium oxide or zirconia 5700 8.5

Dark colour

Rutile 4200 6.0

Chromite 4500 5.5

Magnetite 5200 6.0

It should be noticed that some materials are indicated with their chemical name and/or with the name of their mineral.

The list of materials in the table should not be considered exhaustive and it is possible to use other materials. In particular, it is useful for the material to have a volumic mass greater than or equal to 3800 kg/m³, specifically greater than or equal to 4000 kg/m³ (for example, between 4000 kg/m³ and 6000 kg/m³).

Pale coloured materials may also be useful for coloured binding paste formulations, adding specific dyes or pigments which are compatible with the fluid substance used. Dark coloured materials are usable for black or dark coloured binding paste formulations. The Inventor verified through experimentation that optimum results can also be achieved by mixing the materials indicated in variable proportions. In other words, the powdered substance may be a mixture of powders of different materials. That allows a required volumic mass for the binding paste to be obtained, but giving the best total cost based on the price and the availability on the market of the various materials.

Amongst the materials indicated in the table, the Inventor identified barite (barium sulphate) as particularly useful because, against a quite high volumic mass, it has a low hardness and therefore can easily be ground. Zirconium oxide is also useful because, as well as having a very high volumic mass, it gives the surface of the flooring optimum resistance to wear thanks to its high hardness value.

As regards the particle size distribution of the powder of material with high volumic mass, the Inventor verified through experimentation that a useful range is between 0.1 microns and 300 microns, in particular between 0.5 microns and 200 microns.

Indeed, powders with a particle size distribution lower than 0.1 microns tend to give a binding paste which is too viscous, whilst powders with a particular size distribution higher than 300 microns tend to settle and consequently to separate from the other components, making the binding paste non-homogeneous.

The Inventor also verified that a mixture of powders with two or three different particle size distributions may be useful for obtaining a more fluid binding paste, the volumic mass being equal, than the use of a single particle size distribution.

Examples of advantageous mixtures are provided below.

Example 1 :

• 30% powder with particle size distribution D98 50 microns - D50 10 microns;

• 70% powder with particle size distribution D98 200 microns - D50 50 microns. Example 2:

• 15% powder with particle size distribution D98 30 microns - D50 5 microns;

• 35% powder with particle size distribution D98 100 microns - D50 20 microns;

• 50% powder with particle size distribution D98 200 microns - D50 50 microns.

The percentages refer to the weight. To clarify the indication of the particle size distribution, "D98 50 microns" means for example that 98% by weight of the powder has an equivalent spherical diameter of less than 50 microns.

As regards the fluid substance to be used in the binding paste, in some embodiments the fluid substance is water. In these embodiments the binding paste may also comprise a cementitious binding substance, such as cement powder. Therefore it is a cement-based binding paste and is loaded with powder of material with a high volumic mass.

Examples of cements usable are: Portland cements; aluminous cements or calcium aluminate cements (CAC); calcium sulfoaluminate cements (CSA); "Extreme Style" cement from Sociedade Industrial de Britagem de Pedra; microcements (that is to say, a cement of the previous types, ground to a particle size distribution of less than D98 20 microns).

If necessary it is possible to use a mixture of different cements, to obtain the mechanical strengths, setting times and/or colours best suited to the specific requirements.

In combination with the cement, the binding paste may also comprise one or more additives belonging to the types of additives normally used in the production of concrete. Examples of possible additives are: water reducing additives (in particular polycarboxylate ethers, PCE); anti-bubble or anti-foam additives; fillers with pozzolanic action (silica fume, metakaolin, etc.).

In combination with cement, the binding paste may also comprise a polymer, which may be useful for improving the mechanical performance and chemical resistance of the solidified cementitious binder, in particular as regards the bending strength. In one example of that, a polymer (acrylic or vinyl) powdered and redispersible in water is added in a quantity of between 5% and 20% (in particular between 10% and 15%) of the weight of the cement. In another example, an emulsion of resins (acrylic, epoxy, styrenebutadiene) in water is added in a quantity of between 10% and 30% (in particular between 15% and 25%) of the weight of the cement. These examples are part of the so-called "Polymer-modified concrete" (PMC) family.

In other embodiments, the fluid substance is or contains a polymeric substance, such as a resin or a geopolymer ("geopolymer" indicates a material belonging to a class of synthetic alumino-silicate-based materials which are usable in place of Portland cement). The polymeric substance may also have the function of actual binder. It is a polymeric- based binding paste and is loaded with powder of material with a high volumic mass.

Examples of resins usable are: acrylic resins; epoxy resins; methacrylate resins; polyurethane resins; polyester resins.

Moreover, in addition to the polymeric substance, it is also possible to use all of the additives which are normally used in the production of resinoid compounds, such as: viscosity reducers (in particular epoxy monomers such as C12-C14 alkyl glycidyl ether); anti-bubble or anti-foam additives; viscosity modifier additives; functional fillers (such as micropowders with specific properties).

By appropriately selecting the material, or the materials, for the powdered substance and the quantity of powdered substance in relation to the fluid substance, it is possible to obtain a binding paste (that is to say, a mixture which comprises the fluid substance and the powdered substance, as well as any other components as described above) which has a desired volumic mass value, in particular a volumic mass value which is greater than or equal to 2600 kg/m³ (even more particularly, in a range between 2900 kg/m³ and 3200 kg/m³) and which is suitable for the aims of this invention.

In at least some embodiments, the pieces of solid material (that is to say, the inert material to be mixed with the binding paste and which in the flooring is bound by the solidified binding paste) are pieces of at least one material selected from the materials in the following table, which also indicates the volumic mass or a range of values for it.

Material for the pieces Volumic mass of solid material (inert) (kg/m³)

Quartz 2500

Glass 2400 - 2700

Marble 2600 - 2800

Granite 2500 - 2900

Porphyry 2600

The pieces of solid material used in the mix can be a mixture of pieces of different solid materials.

It should be noticed that a binding paste with a volumic mass value which it is greater than or equal to 2600 kg/m³ has a density which is greater than or just less than the density of the solid materials listed (for example, for all cases it is at least approximately 90% of the density of the solid material), therefore it avoids or significantly reduces sinking of the pieces of solid material in the binding paste, compared with what happens with the same solid material in a prior-art binding paste. Therefore, a binding paste with a volumic mass value which is greater than or equal to 2600 kg/m³ is part of the invention.

Using as the solid material a lighter glass (indeed it should be noticed from the table that the glass may have a volumic mass which is less than 2500 kg/m³, for example 2400 kg/m³, depending on the type of glass) or another lighter material, according to the invention it is possible to use a lighter binding paste, such as a binding paste having a volumic mass value which is greater than or equal to 2500 kg/m³, in particular greater than or equal to 2550 kg/m³. Therefore, a binding paste with this range of volumic mass values is also part of the invention and is suitable for the aims depending on the material for the pieces of solid material.

A binding paste with a volumic mass value which it is greater than or equal to 2900 kg/m³ has a density greater than or equal to the density of all of the solid materials listed, therefore it avoids the sinking for each of them.

In order to make the mix comprising the binding paste and the pieces of solid material, the binding paste according to this invention is also selected based on the solid material selected, in such a way that one of the above-indicated relationships between their densities is complied with.

In one specific way of operating, the fluid substance, the powdered substance and their quantities are selected in such a way that the volumic mass of the binding paste obtained is greater than the volumic mass of the solid material. In other words: the binding paste has a first volumic mass value; the solid material has a second volumic mass value; the first volumic mass value is greater than the second volumic mass value.

If the pieces of solid material are a mixture of different solid materials, the volumic mass to take into consideration may be a volumic mass which is a weighted average based on the respective quantities by volume or (on a precautionary basis) may be the volumic mass of the solid material with the greatest density.

Depending on the difference between the volumic mass values, there may be a reduction in the sinking of the pieces of solid material, a stability or even a floating of the pieces of solid material.

Experiments carried out by the Inventor showed that there is a particularly useful floating effect when the difference between the first volumic mass value and the second volumic mass value is greater than or equal to 4% of the second volumic mass value (in other words, the density of the binding paste is at least 4% more than the density of the solid material), even more particularly when the difference is greater than or equal to 6%.

The Inventor also verified that it is useful for the difference between the first volumic mass value and the second volumic mass value to be less than or equal to 15% of the second volumic mass value (in other words, the density of the binding paste is at most 15% more than the density of the solid material), in particular to be less than or equal to 10%. Indeed, beyond that value the increase in the floating effect does not seem to bring significant advantages or in any case advantages which justify the increase in the cost for the powdered material.

The experiments showed that it is useful for the viscosity of the binding paste (obviously, in the fluid state when the mix is made) to have a value less than 6000 mPa s (for example, between 2000 mPa s and 6000 mPa s), in particular less than 4000 mPa s (for example, between 3000 mPa s and 4000 mPa s).

A viscosity which is too high may hinder floating of the pieces of solid material, but at the same time in order to obtain low viscosity values it is necessary to add a lot of fluid substance (water or resin, with volumic mass around 1000 kg/m³), but this would also reduce the volumic mass of the binding paste. A viscosity range of between 2000 mPa s and 6000 mPa s (or even between 3000 mPa s and 4000 mPa s) was identified as particularly useful when the difference between the first volumic mass value and the second volumic mass value is between 6% and 10% of the second volumic mass value.

Figure 4 shows a first sample 1 and a second sample 2 which were made by the Inventor with a method similar to that described for the prior-art sample 9, but using a mix according to the invention. For both of the samples, the mix was put in a mould up to a height of 15 mm, that is to say, with a lower height than the prior-art sample 95.

The first sample 1 was made using pieces of solid material 11 which is marble and a binding paste 12 which is composed of white cement, barium sulphate (barite) powder, water and a water reducing additive.

The following table indicates the quantities used, the respective volumic masses, the percentage composition and the average volumic mass of the binding paste 12 obtained.

Component Quantity Volumic Volume Mass Volume

(mass in mass (cm³) % % grams) (kg/m³)

White cement 50 3100 16.1 21.7 19.9

Barium sulphate 150 4400 34.1 64.9 42.0

Water 30 1000 30.0 13.0 36.9

Water red. additive 1 1000 1 0.4 1.2

TOTAL 231 2840 81.2 100.0 100.0

As can be seen, the volumic mass of the binding paste 12 is around 5% greater than the volumic mass of the pieces of solid material 11 (2700 kg/m³).

The vertical face 16 of the first sample 1 shows that the pieces of solid material 11 are evenly distributed in the thickness of the sample 1 and have not sunk towards the bottom. The top face 17 of the sample 1 , which had around 1 .5 mm lightly ground from it to make it flat, shows the pieces of solid material 11 and does not have any upper layer formed solely by binding paste 12.

It is easy to understand how, using this mix to make a flooring, it is not necessary to perform deep grinding and no zones or patches are formed in which the pieces of solid material 11 are substantially absent. It should be noticed that, if the pieces of solid material were pieces of quartz (volumic mass: 2500 kg/m³), a similar result would be achievable with a binding paste with volumic mass of around 2600 - 2700 kg/m³: for example, marble powder could be used in place of part of the barium sulphate.

The second sample 2 was made using pieces of solid material 11 which is marble and a binding paste 12 which is composed of white cement, calcium sulfoaluminate cement, barium sulphate (barite) powder, zirconium oxide powder, silica fume, water and a water reducing additive.

Component Quantity Volumic Volume Mass Volume

(mass in mass (cm³) % % grams) (kg/m³)

White cement 25 3100 8.1 12.6 12.1

CSA cement 25 2900 8.6 12.6 13.0

Barium sulphate 65 4400 14.8 32.8 22.3

Zirconium oxide 55 5700 9.6 27.8 14.5

Silica fume 5 2200 2.3 2.5 3.4

Water 22 1000 22.0 11.1 33.1

Water red. additive 1 1000 1.0 0.5 1.5

TOTAL 198 2980 66.4 100.0 100.0

As can be seen, the volumic mass of the binding paste 12 is around 10% greater than the volumic mass of the pieces of solid material 11 (2700 kg/m³).

The vertical face 26 of the second sample 2 shows how the pieces of solid material 11 rose upwards and the excess binding paste 12 remained on the bottom, where a layer 28 formed which is almost exclusively constituted of binding paste 12. The top face Z1 of the sample 2, which had around 1.5 mm ground from it only to make it flat, shows the well distributed pieces of solid material 11 and does not have any upper layer formed solely by binding paste 12.

In this case too, it is easy to understand how, using that mix to make a flooring, it is not necessary to perform deep grinding and no zones or patches are formed in which the pieces of solid material 11 are substantially absent. Thanks to the greater volumic mass (partly because of the presence of the zirconium oxide), the favourable effect due to the binding paste according to the invention is greater for the second sample 2 than for the first sample 1 , where it is however clearly present compared with the sample 95 in Figure 3.

It should be noticed that, if the pieces of solid material were pieces of heavy granite (volumic mass: 2900 kg/m³), a similar result would be achievable with a binding paste with volumic mass of around 3100 - 3200 kg/m³: for example, more zirconium oxide and less barium sulphate could be used.

It should also be noticed that the binding pastes 12 for the sample 1 and for the sample 2 contain a larger quantity of water (by volumetric fraction) than the binding paste 92 for the prior-art sample 95, therefore they are binding pastes which are more fluid and smooth flowing than the prior-art binding paste 92. Consequently, spreading and levelling of the mix are facilitated.

In another embodiment, the binding paste comprises epoxy resin as the fluid substance, barium sulphate powder and zirconium oxide powder as the powdered substances. The following table indicates the quantities used, the respective volumic masses, the percentage composition and the average volumic mass of the binding paste obtained.

Component Quantity Volumic Volume Mass Volume

(mass in mass (cm³) % % grams) (kg/m³)

Epoxy resin A 28 1100 25.5 12.4 34.4

Epoxy resin B 14 1100 12.7 6.2 17.2

Barium sulphate 70 4400 15.9 31.0 21.3

Zirconium oxide 114 5700 20.0 50.4 27.0

TOTAL 226 3050 74.1 100.0 100.0

Using pieces of solid material which are pieces of marble, the result is similar to what is shown for the sample 2.

In another embodiment with resin, the binding paste is composed of epoxy resin (18% by mass) and barite (82% by mass); the volumic mass of the binding paste is around 2850 kg/m³. Figure 5 shows a section of a sample 3 obtained with a mix formed from this binding paste and from pieces of marble. The height of the sample is 10 mm. It can be seen how the pieces of solid material 11 are well distributed in the binding paste 12 throughout the whole thickness of the sample 3.

A method for making a flooring according to this invention comprises the steps of:

• taking pieces of a solid material 11 ;

• making a mix containing the pieces of the solid material 11 and the binding paste 12. The binding paste 12 is selected in such a way as to comply with the desired relationship between the volumic mass of the binding paste 12 and the volumic mass of the solid material 11 , in particular the volumic mass of the binding paste 12 is greater than the volumic mass of the solid material 11 ;

• pouring the mix on a surface to be floored (for example a floor screed, prepared beforehand as in the prior art), so as to form a layer comprising the pieces of the solid material 11 and the binding paste 12;

• after the binding paste has solidified (that is to say, after the layer of mix poured has solidified), grinding the upper surface of the layer, in a similar way to the prior art (with roughing, grinding and polishing steps) but with less thickness to grind. The ground upper surface is the visible surface of the flooring obtained.

The main difference compared with the prior art is in the composition of the binding paste used.

As shown in Figure 2 (which more precisely relates to a sample of flooring made with a mix according to this invention, which was spread with a thickness of 15 mm and which then had 3 mm ground from it) and in Figures 6 and 7 (which are drawings in which the characteristics of interest have been particularly accentuated), a flooring 10 is obtained formed by a layer in which the pieces of the solid material 11 are embedded and bound by the solidified binding paste 12. It is a flooring of the Venetian type, which is poured in place and which has a visible surface 100 which is polished in place. Unlike prior-art Venetian flooring, in the flooring 10 the volumic mass of the binding paste 12 is greater than the volumic mass of the solid material 11.

The binding paste 12 to be used in the mix may be supplied already ready with the desired characteristics, or may be prepared at the required time by appropriately selecting the fluid substance, the powdered substance and their quantities.

Regarding the mix, the volumetric ratio between the pieces of solid material 11 and the binding paste 12 can be selected according to requirements, depending on what is needed and if necessary with values similar to those used for the prior art. In general it is useful for the binding paste 12 to be at least 30% by volume, so as to obtain a mix which is smooth flowing enough when it is poured and in which the pieces of solid material can move. For example, the ratio of the volume of binding paste 12 to the volume of pieces of solid material 11 is 3:2, that is to say, 60% binding paste and 40% solid material. A wider range is between 40% binding paste + 60% solid material and 70% binding paste + 30% solid material. A useful trade-off between the smooth flowing of the mix and aesthetic result is in the range between 55% binding paste + 45% solid material and 65% binding paste + 35% solid material.

Regarding the thickness of the layer of mix to be poured, the Inventor verified that for a cement-based binding paste it is useful to adopt a laying thickness of between 10 and 20 mm, in particular between 12 and 15 mm, whilst for a polymer-based binding paste it is useful to adopt a laying thickness of between 6 and 15 mm, in particular between 8 and 12 mm. As can be seen, they are thicknesses lower than those adopted in the prior art. That allows a saving in terms of material.

The invention described above may be modified and adapted in several ways without thereby departing from the scope of the attached claims.

All details may be substituted with other technically equivalent elements and the materials used, as well as the shapes and dimensions of the various components, may vary according to requirements.

Claims

1. A binding paste (12) for making a flooring (10), the binding paste (12) being a mixture which comprises a fluid substance and a powdered substance, characterised in that the binding paste (12) has a volumic mass value which is greater than or equal to 2500 kg/m³, in particular it is greater than or equal to 2550 kg/m³

2. A binding paste (12) according to claim 1 , wherein the binding paste (12) has a volumic mass value which is greater than or equal to 2600 kg/m³.

3. A mix comprising a binding paste (12) and pieces of a solid material (11 ), the binding paste (12) being a mixture which comprises a fluid substance and a powdered substance, the binding paste (12) having a first volumic mass value and the solid material (11 ) having a second volumic mass value, characterised in that the volumic mass of the binding paste (12) is greater than the volumic mass of the solid material (11 ), the first volumic mass value being greater than the second volumic mass value, the mix being intended to be poured to make a flooring (10) which is formed by a layer of solidified binding paste (12) in which the pieces of the solid material (11 ) are embedded and bound by the solidified binding paste (12).

4. The mix according to claim 3, wherein the difference between the first volumic mass value and the second volum ic mass value is greater than or equal to 4% of the second volumic mass value, in particular is greater than or equal to 6% of the second volumic mass value.

5. The mix according to claim 3 or 4, wherein the binding paste (12) has a viscosity value which is less than 6000 mPa s, in particular is less than 4000 mPa s.

6. The mix according to any one of claims 3 to 5, wherein the pieces of the solid material (11 ) are pieces of at least one material selected from the following materials: quartz; glass; marble; granite; porphyry.

7. The binding paste (12) according to claim 1 or 2, or the mix according to any one of claims 3 to 6, wherein the powdered substance is powder of at least one material which has a volumic mass value greater than or equal to 3800 kg/m³.

8. The binding paste (12) according to claim 1 , 2 or 7, or the mix according to any one of claims 3 to 7, wherein the powdered substance is powder of at least one material selected from the following materials: aluminium oxide or alumina; barium sulphate or barite; zirconium silicate; zirconium oxide or zirconia; titanium dioxide; rutile; chromite; magnetite.

9. The binding paste (12) according to any one of claims 1 , 2, 7 or 8, or the mix according to any one of claims 3 to 8, wherein the fluid substance is water and wherein the binding paste comprises a cementitious binding substance.

10. The binding paste (12) according to any one of claims 1 , 2, 7 or 8, or the mix according to any one of claims 3 to 8, wherein the fluid substance is or contains a polymeric substance, in particular the fluid substance is a resin.

11. Aflooring (10) formed by a layer wherein pieces of a solid material (11 ) are embedded and bound by a solidified binding paste (12), characterised in that the volumic mass of the binding paste (12) is greater than the volumic mass of the solid material (11 ).

12. A flooring (10) according to claim 11 , wherein the layer is formed by solidification of a poured-in-place mix comprising the binding paste (12) and the pieces of the solid material (11 ).

13. A flooring (10) according to claim 11 or 12, wherein the pieces of the solid material (11 ) are pieces of at least one material selected from the following materials: quartz; glass; marble; granite; porphyry.

14. A method for making a flooring (10), the method comprising the steps of:

- taking pieces of a solid material (11 );

- making a mix containing the pieces of the solid material (11 ) and a binding paste (12) which comprises a fluid substance and a powdered substance, wherein the fluid substance, the powdered substance and their quantities are selected in such a way that the volumic mass of the binding paste (12) is greater than the volumic mass of the solid material (11 );

- pouring the mix on a surface to be floored, so as to form a layer comprising the pieces of the solid material (11) and the binding paste (12);

- after the binding paste (12) has solidified, grinding an upper surface of the layer, the ground upper surface being a visible surface (100) of the flooring (10).

15. Use of a powder of a material having a volumic mass value greater than or equal to 3800 kg/m³ in a binding paste (12) to make a flooring (10), in particular the material being selected from the following materials: aluminium oxide or alumina; barium sulphate or barite; zirconium silicate; zirconium oxide or zirconia; titanium dioxide; rutile; chromite; magnetite.

16. Use of a powder of a material according to claim 15, wherein the material is selected from the following materials: aluminium oxide or alumina; zirconium silicate; zirconium oxide or zirconia; rutile; chromite; magnetite.