IL144208A - Aqueous coating composition useful as a protective and decorative coating for structures - Google Patents

Abstract

An aqueous coating composition, useful as a protective and decorative coating for structures, comprising: (a) a cross-linkable polymer binder comprised of magnesium oxychloride cement; (b) at least one filler; (c) at least one phosphoric acid salt; (d) reinforcing silica; (e) a water-repellent; (f) water.

Description

AN AQUEOUS COATING COMPOSITION, USEFUL AS A PROTECTIVE AND DECORATIVE COATING FOR STRUCTURES FIELD OF THE INVENTION The present invention relates to an aqueous coating composition for protection and decoration of structures, especially useful for coating walls of structures made of Portland cement or slaked lime.

BACKGROUND OF THE INVENTION House painting has been known for several thousand years. Slaked lime came into use for this purpose approximately 2500 years ago, for protection and decoration of house walls. In the past 200 years, cement has become a central building material in the construction industry, especially in cinder blocks and construction casting. Cement walls can be covered with a protective or a leveling layer of plaster coating based on silica sand, cement or lime. A protective covering layer is termed a "paint" or a "coating", based on the thickness of a dried layer of paint or coating. When the thickness of a dried layer is below or equal to 100 microns, the layer is termed a "paint"; when the thickness is 100 to 300 microns, it is termed a "multi-layered paint", and when the thickness is above 300 micron, a "coating".

In the last 100 years, buildings and structures built from cement materials have been subjected to increased wear. This is due to increased air pollution with compounds such as S02, N02, N04 and especially C02. These pollutants have become more plentiful with the expansion of industry. Since these pollutants are also present in exhaust gases emitted from automobiles, the rise in the number of motor vehicles has likewise lead to an increase in their presence. These pollutants combine with water vapor present in the air, and precipitate as "acid rain". Walls made of materials based on cement and lime have an alkaline nature. Therefore, acid rain can interact with and destroy these walls. This phenomenon is known as "decarbonization". Moreover, houses built on land near natural underground reservoirs, or near the ocean, suffer from the effects of these waters and their alkaline solutes, which can cause structural and aesthetic harm to the external walls of the house. External paints and coating therefore, have become more important in protecting structures from wear.

In recent decades, producers of paints have developed coatings for external and internal house walls, having a broad range of textures and tints, to protect the house walls and grant them an aesthetic appearance. At present, the majority of paints and coatings produced for house-painting are water-based as opposed to being oil-based. The reasons for preference of water-based paints and coatings are their easy use, capability to be diluted with water, the absence of undesirable odors, their relative environmental and health safety, and the ease in cleaning the painting equipment and accessories. Today most architectural coatings and paints are comprised of binders, fillers, pigments and various additives which impart technologically advantageous properties to the final product. Binders are polymer materials which ensure the setting, binding and adhesion between the components of paints and coatings. The properties of the binders are the most important among the properties of all the components, since on the whole, the properties of the binder determine the properties of the paint or coating. Pigments impart tints and spreading capacity to paints and coatings. Fillers, which are often mineral complexes of various dimensions, and less often organic matter such as sawdust and cork, impart stability to the matrix and additional volume and weight.

In the majority of paints and coatings produced today, the binder is based on a synthetic polymer. Drying and adhesion of these paints and coatings relies on penetration of the binder into the surface being painted, to seize micro-particles contained in the surface. As water evaporates from the paint, polymer particles that are in emulsion approach and contact each other to bind into a continuous uniform polymeric film which connects and envelopes the pigments and fillers. The force granting these paints adhesion to the surface being painted, is exclusively mechanical, and the magnitude of the adhesion is sufficient to keep several layers of paint on the wall. Paints and coatings based on synthetic polymers are widely applied, since they form a waterproof polymer film, which protects walls from moisture. However, these coatings have a number of drawbacks. Ultraviolet radiation present in sunlight tends to age the polymeric film with time. The film changes its color, and becomes inelastic and prone to cracking. When cracks appear, the walls beneath become water permeable, and moisture penetrates under the film to destroy adhesive bonds between the paint film and the wall. Another drawback of coatings based on synthetic polymers is that they are impermeable to gasses, and do not allow, for instance, release of gasses exhaled by the occupants though the coating and the wall to the outside of the building.

A minority of coatings and paints are mineral-based. Mineral-based coatings include silicate paints, polymer-cement paints and compositions based on slaked lime. However, these coatings are highly water-permeable and thus have a short life, therefore they have not found broad application.

The need exists for a water-based paint or coating, which is resistant to crack formation, is water-impermeable, and is able to withstand the effects of the environment, such as acid rain.

Magnesium oxychloride cement is a cement used in the building industry to cast floors in public buildings, to repair structural damage, and to cast abrasive wheels used for grinding. Magnesium oxychloride cement is also known as "Sorel cement", "French cement", "magnesite cement" and "magnetic cement". The reaction through which it is formed was discovered by Sorel in 1867, and most often nowadays the cement is formed by mixing magnesium oxide with an aqueous solution of magnesium chloride. Magnesium oxychloride cement posses many properties superior to those of other widely used cements such as Portland cement. It does not require wet curing, it has a high degree of fire resistance, and a low thermal conductivity. It is mechanically strong, having a high resistance to abrasion, and high strengths of compression, bending, crushing and transverse strength. It bonds well to various inorganic and organic aggregates, such as saw dust, wood flour, marble flour, silica sand and gravel and therefore can be combined with aggregates which are not suitable for use in Portland cement. The resulting magnesium oxychloride cement posses mechanical strength, insecticidal properties and low heat conductivity, and is unaffected by oil grease and paint. Its hardening is rapid; a cement can be formed having a compressive strength of 100 MPa as measured after 28 days. U.S. Patent No. 5,110,361 discloses magnesium oxychloride cement compositions useful for structural repair and for application as stucco upon external walls. U.S. Patent No. 6,200,381 discloses a binder of magnesium oxychloride cement and a dolomite, and U.S. Patent No. 5,679,119 discloses magnesium oxychloride cement having fibers and abrasive grit within, useful for casting grinding tools.

The main drawback of magnesium oxychloride cement is its sensitivity to humidity. When immersed in water, magnesium oxychloride cement absorbs moisture at up to 5-15% of its initial weight (depending on its formulation) and its strength is reduced by 40-60% due to dissolution of the oxychloride crystals. Although the cement regains its strength upon drying, while wet it is vulnerable to abrasion and erosion, and loss of certain amounts of MgCl2. For this reason magnesium oxychloride cement has been applied in construction mostly to the interiors of buildings, and not to exterior surfaces.

Attempts have been made to impart magnesium oxychloride cement with water resistance, by application of an external water-resistant protection coat, with moderate degrees of success. The effectiveness of the external coat depends considerably on the completeness of the application and its coverage; the coating must be renewed at frequent intervals. A considerable number of admixtures or additives have been proposed for the waterproofing of magnesium oxychloride cement, for example, copper metal or oxide, phosphates, various natural gums and polymeric compounds. However, many of these proposed additives had adverse effect on the properties of the cement. The need exists for a magnesium oxychloride cement composition which posses the advantages of this type of cement, yet is inherently water resistant.

It is the object of the present invention to provide a coating composition which is mechanically strong, yet is water impermeable and is resistant to acids and bases. The composition of the present invention is especially useful to coat exterior and interior walls of buildings or structures made of Portland cement or slaked lime, however the scope of the invention is not limited to the painting of structures constructed of only the above-mentioned materials.

These and other objects of the present invention will become more apparent from the detailed description of the preferred embodiments, that follows.

DEFINITIONS "Fillers" are materials that are added to paints and coatings to stabilize the paint or coating and add additional volume and weight. Examples are mineral complexes or organic matter such as sawdust and cork.

The term "magnesium oxychloride cement" refers to "Sorel cement", and these terms may hereby be used interchangeably.

SUMMARY OF THE INVENTION There is thus provided in the present invention, an aqueous coating composition, useful as a protective and decorative coating for structures, comprising: a) a cross- linkable polymer binder comprised of magnesium oxychloride cement; b) at least one filler; c) at least one phosphoric acid salt; d) reinforcing silica; e) a water-repellant; f) water.

According to one preferred embodiment of the present invention, the cross-linkable polymer binder is comprised of magnesium oxide and magnesium chloride hexahydrate that form the magnesium oxychloride cement. In this case, preferably the concentration of the magnesium oxide is 5-15% by wt. of the composition. In one preferred embodiment, the concentration of magnesium chloride hexahydrate is 10-20% by wt. of the composition. In another preferred embodiment, the ratio of magnesium oxide to magnesium chloride hexahydrate is within the range of 1 part magnesium oxide to 1.8 parts magnesium chloride hexahydrate; to 1.2 parts magnesium oxide and 1 part magnesium chloride hexahydrate.

Additionally, according to one preferred embodiment, the filler is selected from carbonate rock, or silica sand.

Moreover, in certain embodiments the particle sizes of the above-mentioned fillers (carbonate rock, silica sand) is 10-3000 micron.

Further, in one preferred embodiment the phosphoric acid salt is selected from sodium dihydrophosphate, or phosphoric acid. The phosphoric acid salt will then preferably be present at a concentration of 0.5-2.5% by wt. in relation to the concentration of the magnesium oxychloride cement polymer binder.

Still further, in one embodiment of the present invention, the reinforcing silica is present at a final concentration of 5-10% by wt. of the composition.

Moreover, in one embodiment the reinforcing silica preferably has a particle size of approximately 20 micron.

In addition, in a preferred embodiment, the water-repellant is selected from an aluminum stearate, or a calcium stearate. In this instance, the water repellent is preferably present at a final concentration of 0.5-5% by weight of the composition.

Further, in this instance, in another preferred embodiment, the water repellant is in the form of a chalk comprised of CaC03 coated with a calcium stearate.

Still further, in a preferred embodiment, the composition additionally comprises polyethylene fibers. Preferably these fibers are present at a final concentration of 0.2-0.6% by wt. of the final concentration.

Moreover, in certain embodiments, the composition additionally comprises a pigment. Preferably, the pigment is an iron oxide pigment.

DETAILED DESCRIPTION OF THE INVENTION It is appreciated that the detailed description that follows is intended only to illustrate certain preferred embodiments of the present invention. It is in no way intended to limit the scope of the invention, as set out in the claims.

In general, the present invention discloses a coating composition having a magnesium oxychloride cement binder, which grants the coating mechanical strength, and a water repellant component which imparts water resistance to the coating. Magnesium oxychloride cement was not used in prior art in compositions for painting or coating house walls, rather it was usually applied in the construction industry as a structural component used to form floors, or to repair damage to walls made of Portland cement. Prior art technique did not allow thin layers of Sorel cement to be formed, and thus until now, this type of cement was not applicable in paints and coatings, which by definition have thin dried layers. Sorel cement was used, for example, in prior art in plaster or stucco compositions which tend to be 3- 10mm thick; while even the thickest paint layers, termed "coatings", are thinner, at approx. 0.3-0.9mm. The present invention is the first application of Sorel cement as the principal component of a coating for protection and decoration of house walls, and especially of house walls made of Portland cement. The coating disclosed in the present invention can also be applied to walls constructed of materials other than Portland cement.

More specifically, the present invention relates to an aqueous coating composition, comprised of at least a cross-linkable polymer binder consisting of magnesium oxychloride cement, at least one filler, at least one phosphoric acid salt, reinforcing silica, a water-repellant, and water. Each of these components is hereby described below.

Magnesium oxychloride cement is generally made by adding calcined magnesia powder, also known as magnesium oxide (MgO), to a strong solution of aqueous magnesium chloride, and mixing. The reaction that occurs, termed the "Sorel reaction", results in formation of the cement. An inorganic polymer is formed, having octahedral crystals bound to one another via hydrogen bonds. The rate of reaction is dependent upon the inherent activity of the specific magnesium oxide chosen, the ratio of the reactants, and the temperature. In the present invention, magnesium oxide is mixed with magnesium chloride hexahydrate, at a ratio within the range of (1):(1.8) to (1.2):(1), which correlates to a final concentration of 5-15% (wt.) of magnesium oxide and 10-20% (wt.) of magnesium chloride hexahydrate within the final composition. The mechanical strength of the binder can be controlled by varying the concentration of the magnesium chloride.

Generally in Sorel cements, the magnesium oxide powder component is mixed "on site" with the liquid magnesium chloride component; in the present invention the coating can be applied to a surface up to six hours after this mixing is performed.

The filler to be used can be selected from a wide variety of fillers, according to the required characteristics of the final composition. The method by which the paint is applied must also be taken into consideration upon selection of a filler, since certain fillers impart a high viscosity, which prevents application of the coating via spraying. Preferred fillers are inorganic mineral complexes of calcium carbonate (CaC03) having a particle size of 0.01 -2mm, at a concentration of 4-50% by weight of the final composition.

The composition also contains a phosphoric acid salt. During polymerization of the coating, this salt dissolves to release phosphate ions that stabilize the crystals of binder which make up the Sorel cement, through interaction with and stabilization of the hydrogen bonds present between the crystals. This Preferred phosphoric acid salts are sodium dihydrophosphate (NaH2P04) or phosphoric acid (H3P04), at a preferred concentration of 0.5- 2.5% by weight of the composition.

The coating composition contains reinforcing silica (Si02) as well, which acts to bind calcium hydroxide present in the wall being coated (calcium hydroxide is a component of walls made of Portland cement and of slaked lime). The bonds formed grant adhesion of the coating to the surface being coated, and moisture-resistance to the coated surfaces. Preferred concentrations of reinforcing silica are 5-10% by weight of the composition.

The coating includes a water repellant, which grants the Sorel cement water-resistance. Preferred water-repellants are calcium stearates, or aluminum stearates, at a preferred concentration of 0.5-5% by weight, of the composition. The stearate can be added in the form of a chalk coated with stearate. The presence of a water-repellant within the composition imparts the Sorel cement with a higher degree of water-resistance than is attained in the prior art method of application of an external water-resistant layer over the Sorel cement. Additionally, inclusion of a water-repellant within the coating allows passage of gasses and vapors through the coated wall, which is favorable.

The coating can optionally contain polyethylene fibers which prevent cracking of the coating over time, by strengthening the bonds between the crystals. The addition of fibers in the composition allows shrinkage and expansion of the coating in response to changes in the environment, without cracking of the coating. Polyethylene fibers additionally ensure the filler component remains in suspension while the coating is wet. Polyethylene fibers are preferably present at a concentration of 0.2-0.6% by weight of the total composition.

The coating can optionally contain a pigment. Preferred pigments are iron oxide pigments.

The wall to be covered with the coating must be free of dust, and must be pre-moistened before application of the coating. The coating can be applied either by spraying or by plastering it onto the surface being coated. The room temperature should preferably be within the range of 5-36°C.

Sorel cements seem particularly suited for protective coatings of house-walls, due to their high mechanical strength and hardness, chemical resistance to acids and bases, their chemical affinity to common components of walls which results in adhesion of the coating to the surface being painted, and the presence of chloride and hydroxide ions which grant the coating antibacterial properties. Coatings of the present invention were found to have acceptable properties for the coating of structures when tested according to Israeli standards No. 1920 (part 1), which relates to the standards of plaster coating, and standard No. 1731, which relates to synthetically-based textured coatings. Most tests were performed according to Standard No. 1920, the minority being performed according to Standard No. 1731. Results of these tests were as follows: 1. Minimal adhesion forces allowable are 0.5 Mpa, and coatings according to the present invention possessed adhesion forces of 1.1-1.5 Mpa. After tests of accelerated wear, adhesion was 0.96 Mpa, while the minimal allowable value is 0.2Mpa. 2. The coatings are resistant to UV radiation, due to the presence of mineral fillers within. After 1000 hours of UV irradiation at strengths described in Israeli standard No. 1731, the appearance of the coating was unchanged and no cracking occurred. 3. Water permeability was tested according to Israeli standard No. 1920. Maximal allowable capillary rise is 0.5 kg/m2 x hour 1/2 , and coatings of the present 2 1/2 invention scored a capillary rise of 0.03-0.1 kg/m x hour . 4. Vapor permeability was acceptable according to Israeli standard No. 1920. 5. Wear resistance under aggressive climate conditions was tested. Maximum allowable mass loss under seaside climate conditions is 7%, and coatings of the present invention scored 1.8%. The strength of the coating was found to have increased under these conditions, by 38.7%. 6. The coating was found to be stable against fungi. Magnesium chloride was found to evaporate to a small degree from the coating, at a level deemed harmless.

Israeli Standards No. 1920 and 1731 are based on the following American and European standards: ASTM C-151-93a | DIN 52615-1987 | BS 455 | part 1-1998 ASTM C-109 M-95 | DIN 1 168p 1975 | ASTM C-231-91b BS 1014-1992 I BS 3148-1980 EXAMPLES Example 1 A coating composition was formulated, for use as an external or internal coating of walls made of cement, cement-lime, or concrete or silicate blocks or stones. The coating is a two-layered coating; the undercoat is smooth, while the overcoat is textured.

Overall, the two-layered coat posses a water permeability of 0.03 kg/m X hour1/2; a vapor permeability of 1.06 m; and an adhesion value of 1.3 MPa. Both layers are applied by pressurized spraying of the coating. The overcoat is applied 2-3 hours after the undercoat is applied. It is necessary to use 2-4kg of coating for every square meter of wall.

To prepare the undercoat, the liquid components are first mixed together as follows: 1. NaH2P04 salt, at a concentration of 0.2-0.3% by weight of the total composition, is dissolved in water till total dissolution; the water content must not exceed 13-18% by weight of the total composition. 2. Magnesium chloride hexahydrate is added at a cone, of 8-13% by weight of the total composition, and mixed till dissolution. 3. Polyethylene fibers are added at a cone, of 0.2-0.3% by weight of the total composition, and mixed to wet the fibers and distribute them uniformly.

The liquid part thus prepared can be stored as long as six months in a plastic container placed in cool dry conditions.

The powder part of the undercoat is prepared by mixing the dry ingredients as follows: 1. Calcium carbonate (CaC03) is used, having a crystalline marble-like structure, ground to pellets having a maximum diameter of 0.6mm. The calcium carbonate is used at a cone. Of 45-50% by wt. of the total composition. This is mixed with chalk coated with stearic-acid; the coated chalk is added at a cone, of 3-5% by wt. of the final composition (the stearic acid coating has a thickness of approx. 10μ). 2. Reinforcing silica having a particle size of 20μ is added at a con. of 2-4% by wt. of the total composition, and mixed. 3. Magnesium oxide (MgO) (95% of which has a particle size of <75μ) is added at a cone, of 5-8% of the total composition, and the powder part is mixed till uniformity.

The powder part can be stored in plastic bags in a cool, dry place for up to six months.

The overcoat also contains a powder part and a liquid part. The liquid part of the overcoat is prepared by mixing the following liquids: 1. Water at 15-20% by weight of the total composition. 2. Sodium dihydrophosphate at 0.2-0.4% by weight of the total composition. 3. magnesium chloride hexahydrate at 6-11% by weight of the total composition. 4. polyethylene fibers at 0.3-0.5% by weight of the total composition.

The powder part of the overcoat is prepared by mixing the following dry components:: 5. calcite, a 0-0.6 mm fraction at 25-35%) by weight of the total composition. 6. calcite, a 0.6-1.0 mm fraction at 4-6% by weight of the total composition. 7. calcite, a 1.0-1.2 mm fraction at 15-20% by weight of the total composition. 8. chalk with stearic acid coating, having a particle size of 10 micron, at 12-35% by weight of the total composition. 9. Magnesium oxide at 4.5-7.5% by weight of the total composition.

Example 2 A coating was formulated for use in the repair of a textured coating on cement or cement-lime walls. Often an old textured coating contains areas where the texture has been destroyed. The coating described here can be applied over this to rejuvenate the texture, and the old coating need not be removed, only cleaned from dust, and if necessary, deep holes can be leveled with plaster before the new coating is applied. The coating is water-resistant and aesthetic, and has an adhesion value of 1.4 Mpa, thus it strengthens the old coating.

This coating is also a two-layered coating, with each layer comprised of a liquid part and a powder part, which are prepared separately, then mixed together on-site.

The liquid part of the undercoat contains the following components (concentrations noted hereby and noted below represent the percentage of the component as measured by weight, relative to the total composition): - water - 15-20% - phosphoric acid - 0.1 -0.2% - magnesium chloride hexahydrate - 5 - 10% - polyethylene fibers - 0.2-0.3%.

The powder part of the undercoat contains the following components: - calcite, 0-0.6 mm fraction - 40-45% - chalk with hydrophobic coating (stearic acid), 10 micron fraction - 3-5% - reinforcing silica, 20 micron fraction - 5-10% - calcinated magnesia - 4-7%.

The liquid part of the overcoat is composed of the following: - water - 15-20% - phosphoric acid - 0.1 -0.2% - magnesium chloride hexahydrate - 5 - 10% - polyethylene fibers - 0.3-0.5%.

The powder part of the overcoat is composed of: - calcite (0-0.6 mm particle size) - 25-35% - calcite (0.6-1.0 mm particle size) - 10-20% - calcite, (1.0-1.2 mm particle size) - 15-20% - chalk coated with stearic acid ( 10 micron fraction ) - 10- 15% - calcinated magnesia - 4-7%.

The two-layered coating is applied using pressurized spraying, and minimally two coats are used. An interval of two to three hours is necessary before each additional coat is applied. 3-5 kg of coating is consumed per square meter of wall.

Liquid parts and dry powdered parts can be stored separately as in Example 1.

Example 3 A decorative coating was formulated for use in renewal and repair of internal and external walls, especially for use in coating walls constructed of cement, cement-lime, concrete and gypsum. This coating has a fine-grained texture, and is applied in several layers, at a minimal total thickness of 0.8mm. Application is via handheld tools used in decorative plastering, such as a trowel, or a foam block, to walls that have cleaned from dust and moistened with water. 2-3 kg of coating are consumed for every square meter of wall coated.

The liquid part is comprised of the following (concentrations noted are percentage of each component out of the total composition, as measured by weight): - water - 10-15% - sodium dihydrophosphate - 0.3-0.4% - magnesium chloride hexahydrate - 6- 1 1 % - polyethylene fibers - 0.5-0.6%».

The powder part is comprised of: - calcite, 0.1 -0.6 mm fraction - 35-40% - chalk coated with stearic acid ( 10 micron fraction ) - 10- 15% - reinforcing silica, fraction (20 micron fraction ) - 5% - silica sand (60 micron fraction ) - 10% - magnesium oxide - 5-8%.

The liquid and the powder parts can be stored separately for up to six months (as described in Example 1). To form the coating, the liquid and power parts are mixed together on-site. The coating formed has a capillary rise of 0.1 kg/m2 x hour1/2, a vapor permeability of 1.5 m, and an adhesion value of 1.13 Mpa.

Example 4 A coating was formulated for the coating of structures situated in areas of high humidity, such as near underground reservoirs, or near the sea. The coating has high degrees of water resistance, mechanical strength, adhesion and chemical stability, being resistant to the acids and salts present in underground reservoirs.

The liquid part of the coating is comprised of the following (concentrations are percentages of each component, relative to the total composition, as measured by weight): - water - 10-12% - sodium dihydrophosphate - 0.3-0.5% - magnesium chloride hexahydrate - 10-12% - polyethylene fibers - 0.5%.

The powder part is comprised of the following components, added in the order listed, and mixed after each addition: - silica sand, (particle size of up to 200 micron) - 40-50% - aluminum stearate - 1-5% - silica sand, (particle size of up to 60 micron) - 10-15% - magnesium oxide (95% of which has a particle size of <75μ; and the magnesium oxide having an iodine index activity of 2-6) - 10-14%.

The liquid and powder parts are mixed together on-site, and applied using a handheld tool such as a trowel, till a layer of at least 5mm in thickness is achieved.

Claims (18)

1. An aqueous coating composition, useful as a protective and decorative coating for structures, comprising: < a), a cross-linkable polymer binder comprised of magnesium oxychloride cement; b) at least one filler; c) at least one phosphoric acid salt; d) reinforcing silica; e) a water-repellant; f) water.

2. The coating composition of claim 1, wherein the cross-linkable polymer binder is comprised of magnesium oxide and magnesium chloride hexahydrate that form the magnesium oxychloride cement.

3. The coating composition of claim 2, wherein the concentration of magnesium oxide is 5-15% by wt. of the composition.

4. The coating composition of claim 2, wherein the concentration of magnesium chloride hexahydrate is 10-20% by wt. of the composition.

5. The coating composition of claim 2, wherein the ratio of magnesium oxide to magnesium chloride hexahydrate is within the range of 1 part magnesium oxide to 1.8 parts magnesium chloride hexahydrate; to 1.2 parts magnesium oxide and 1 part magnesium chloride hexahydrate.

6. The coating composition of claim 1, wherein the filler is selected from carbonate rock, or silica sand.

7. The coating composition of claim 6, wherein the particle size of said filler is 10-3000 micron.

8. The coating composition of claim 1, wherein the phosphoric acid salt is selected from sodium dihydrophosphate, or phosphoric acid.

9. The coating composition of claim 8, wherein the phosphoric acid salt is present at a concentration of 0.5-2.5% by wt. in relation to the concentration of the magnesium oxychloride cement polymer binder.

10. The coating composition of claim 1, wherein the reinforcing silica is present at a final concentration of 5-10% by wt. of the composition.

11. The coating composition of claim 1 , wherein the reinforcing silica has a particle size of approximately 20 micron.

12. The coating composition of claim 1 , wherein the water-repellant is selected from an aluminum stearate, or a calcium stearate.

13. The coating composition of claim 12, wherein the water repellent is present at a final concentration of 0.5-5% by weight of the composition.

14. The coating composition of claim 12, wherein the water repellant is in the form of a chalk comprised of CaC03 coated with a calcium stearate.

15. The coating composition of claim 1, additionally comprising polyethylene fibers.

16. The coating composition of claim 15, wherein said fibers are present at a final concentration of 0.2-0.6% by wt. of the final concentration.

17. The coating composition of claim 1, additionally comprising a pigment.

18. The coating composition of claim 17, wherein the pigment is an iron oxide. For the Applicants RE1NH0LD CQHN AND PARTNERS