A gypsum plaster composition and a method of manufacturing the same

Abstract

The present application provides a gypsum plaster composition, comprising 25 to 75 % of gypsum plaster; 25 to 75 % of filler; 0.005 to 0.1 % of retarder; 0.015 to 0.1 % of heat resistant accelerator; 0.05 to 0.5 % of modified cellulose ether; 0.05 to 3 % of re- dispersible polymer; and 0 to 0.5 % of coloring agent. Such a gypsum plaster composition exhibits improved direct adhesion on a reinforced cement concrete (RCC) surface. Further the application also provides a method of manufacturing a gypsum plaster composition and method of applying the same.

Description

[0001] A GYPSUM PLASTER COMPOSITION AND A METHOD OF

[0002] MANUFACTURING THE SAME

[0003] TECHNICAL FIELD

[0004] The present disclosure relates in general to a gypsum plaster composition. More particularly, the present disclosure provides a gypsum plaster composition with specific additives and retarders. Such a gypsum plaster composition can be applied directly on a RCC substrate.

[0005] BACKGROUND

[0006] Gypsum is a common mineral composed of calcium sulfate dihydrate. It is an abundant and easily accessible mineral on the Earth’s surface, which has been extensively processed and used by humans since the Neolithic period for different decorative and construction purposes. It is widely mined and is used as a fertilizer and specifically as the main constituent in many forms of plaster, blackboard / sidewalk chalk, and dry wall etc. A massive fine-grained white or lightly tinted variety of gypsum is used for sculpture. The gypsum is used for variety of gypsum products, most used as building materials, with an example being wallboard and fiberboard sheets, for many reasons. They are easily manipulated to make continuous walls of desired shapes and sizes. They are durable, easily installed, patched, and have beneficial insulation, fire and acoustic properties. Decorative finishes, such as wallpaper or paint readily adhere to surfaces to allow for a large variety of decorating options.

[0007] More particularly, gypsum plasters can be applied to brick walls, concrete blocks, or reinforced cement concrete (RCC) surfaces. Gypsum plasters usually come in ready to mix bags, in which the powder can be extracted in a dry vessel and then mixed with water. The mixture is to be stirred for 2-3 minutes and based on desired thickness of plaster it can be applied on the wall. Application is also extended to ceiling & common areas, for example, parking lots, staircase underlayment & basement.

[0008] Rapid and evolving changes in construction technology from brick to smooth RCC (Mivan technology) is being seen, to achieve less undulated surface. However, this has resulted in plastering thickness requirement which drastically dropped from 12 mm to 6 mm, which in turn mandates increased plastering quality requirement. Generally, wall putty and standard levelling gypsum plaster cannot withstand at such low thickness due to poor water retention property which further leads to crack and delamination. This further necessitates an additional layer of bonding agent on RCC for improved adhesion of gypsum plaster (in particular). Beyond this, it would further require finishing with primer and paint.

[0009] Traditionally, plastering and finishing in hot and humid climate areas, usually consists of an undercoat plaster followed by finishing with putty, primer and paint. Putty is a white cement-based formulation available in dry mix powder as well as acrylic ready- to-use paste. Putty is an air-drying product with limited thickness build-up of approximately 3mm, which usually takes 3 days including curing and coating (4-6 mm not possible in one coat application). Also, the applicators are different for plastering and finishing which usually add up the labor cost by the usage of multiple applicators for every step.

[0010] In general, the application of gypsum plaster is a labor-intensive operation, in particular the summer in hot and humid climatic conditions may result in poor workability and insufficient hydration due to rapid water evaporation or removal from the plaster. Thus, various additives are added to the gypsum plaster to enhance viscosity, workability, or water retention, adhesion onto substrate etc. In the existing state of art various proposals of gypsum plaster finish have been made, for ex., a composition mainly composed of an inorganic powder such as mortar, plaster, gypsum, or diatomaceous earth is kneaded with water to form a wet coating material in the form of a slurry, and the wet coating material is used for the interior and exterior of a building. WO 2015 / 150319 describes a gypsum composition containing a mixture of calcium aluminate and calcium sulfate hemihydrate, anhydrite or calcium sulfate dihydrate in a weight ratio of from 1: 1 to 1:5 and fillers. WO 2008 / 003672 Al describes gypsum-based smoothing compounds that contain, as the binder component, a source of reactive sulfates.

[0011] JP6735290B2 document provides a dry setting type plaster composition for coating material capable of forming a coating film in which color unevenness is suppressed while being thin and smooth, when a gypsum coating material is prepared by adding water.

[0012] On the other hand, various cellulose ethers and derivatives thereof produced from natural cellulose pulp are widely used as additives to construction materials such as mortar or plaster using cement or gypsum as a binder, for the name of a thickener, a water retention agent or a material separation reducing agent or the like. In particular, the major reason that cellulose ethers are used as gypsum plaster additives is that the cellulose ethers incorporated in gypsum plasters exhibit unique functions such as repair action and thickening action, thereby being effective in preventing material separation, increasing adhesion, increasing strength of the thick plaster, and preventing cracks, etc.

[0013] US 2005-0241541 document discloses a gypsum plaster using high viscosity cellulose ether manufactured from raw cotton linters, and said method describes that the water repellency, sag resistance, and workability of the gypsum plaster may be improved, and the usage amount of the cellulose ether may be reduced. However, there is a problem in that when the cellulose ether composition is used in a gypsum plaster, nonunwinding gypsum lumps are generated in water, and consequently, to eliminate the same, working time of operators increases or when applied to a wall surface or the like, uneven plaster surface occurs, lumps, and the like, and the quality of the final working result is reduced.

[0014] Korean Patent No. 2011-0082857 discloses a plaster additive composition for a gypsum-based finish containing cellulose ether, polyacrylamide and guar gum, and according to this method, primary taste workability is improved by including guar gum in the additive composition. However, in the secondary surface pureness work which is conducted after approximately 5 to 30 minutes after the primary fine bowel work, the retention property of the gypsum plaster is reduced and the viscosity is increased and the plaster is embedded, and hence the workability is reduced, thereby resulting in a phenomenon in which the work surface is roughened. As such, there is a problem in that work efficiency is lowered since there is no sufficient pot life (main life) required for the primary construction and secondary solid working cannot be secured.

[0015] The existing state of art in one way or the other only improves one or more of the functionalities of the gypsum plaster. As the thickener composition used in gypsumbased finishing plasters, an improved cellulose ether-based thickener composition with improved properties can be used to improve thickening effect. The improving cellulose ether thickener composition comprises at least one physical property improving additive which is anionic, neutral, or cationic and has thickening, adsorbing and flocculating effects, and the strong adsorbing and flocculating effects of the physical property improving additive increases the thickening effect of the thickener. However, while the use of such an improved cellulose ether-based thickener composition can improve the thickening effect of gypsum-based finishing plaster, the problem arises that the ease of construction work is significantly reduced due to the strong cohesive force of the improved thickener composition.

[0016] Further, increasing the content of the additive for improving physical properties in the improved cellulose ether-based thickener composition lowers the water retention property, which is the intrinsic property of the cellulose ether, and thereby causes problems such as deterioration in workability. That is, the deterioration of the water retention, which is the main physical property of cellulose ether, improves the initial marginal performance after kneading of plaster composition and water; In the secondary cotton smoothing operation performed approximately 5-30 minutes after the primary camouflage operation, the performance is reduced due to deterioration in water retention, thereby causing a phenomenon in which the working surface becomes rough, and thus, a sufficient time between the secondary cotton smoothing operations after the primary construction is not ensured, and thus there is a problem in which the working efficiency is reduced.

[0017] Hence, it is understood that adding cellulose ether alone cannot contribute to any improved properties of the gypsum plaster. Also, the state of art lacks on a single coat or only one formulation which functions as a plaster, putty, primer, and paint. Therefore, there is a desire to develop gypsum plaster finish which is an alternative to putty, primer, and paint at the same time. A single direct application of gypsum plaster finish serves the customers need in terms of both technical and economic significance.

[0018] OBJECT OF INVENTION

[0019] The main object of the present invention is to provide a gypsum plaster composition with improved adhesion on a reinforced cement concrete surface. Particularly, another object of the present invention is to provide a gypsum plaster composition which can be applied directly as a monolayer on a reinforced cement concrete surface.

[0020] Yet another object of the present invention is to provide a gypsum plaster composition which avoids the application of putty, primer, and paint.

[0021] Further, yet another object of the present invention is to provide a method of manufacturing of a gypsum plaster composition, and a method of applying gypsum plaster composition on a reinforced cement concrete surface.

[0022] The present disclosure was developed by outlining the above objectives.

[0023] SUMMARY OF THE DISCLOSURE

[0024] In an aspect of the present disclosure, a gypsum plaster composition is disclosed. Said gypsum plaster composition comprises 25 to 75 % of stucco; 25 to 75 % of filler; 0.005 to 0.1 % of retarder; 0.01 to 0.1 % of heat resistant accelerator; 0.05 to 0.5 % of modified cellulose ether; 0.05 to 3 % of re-dispersible polymer; and 0 to 1 % of coloring agent. Such a gypsum plaster composition exhibits improved direct adhesion on a reinforced cement concrete surface.

[0025] In another aspect of the present disclosure, a method of manufacturing a gypsum plaster composition is disclosed. Said method comprises the steps of mixing the stucco, filler, retarder, heat resistant accelerator, modified cellulose ether, re-dispersible polymer and coloring agent until a uniform, homogeneous dry mix is formed. Further added to the dry mix is water (here 40-50wt.%), to form a lump-free consistent slurry. In yet another aspect of the present disclosure, a method of applying gypsum plaster composition on a reinforced cement concrete surface is disclosed. Said method comprises the steps of coating the pre-wetted surface of the RCC substrate with the gypsum plaster slurry. The applied coating is troweled to smoothen the coat. Further, optionally a diluted coat of less than 1 mm is applied before set within the setting time of plaster.

[0026] Other features and aspects of this disclosure will be apparent from the following description and the accompanying drawings.

[0027] DETAILED DESCRIPTION

[0028] As used herein, in every embodiment, it must be understood that the term ‘additive(s)’ or ‘modifier(s)’ can be used interchangeably, refers to additional components included in the base gypsum plaster composition.

[0029] The term ‘adhesion’ as used herein, refers to the tendency of the gypsum plaster composition to firmly cling on to the reinforced cement concrete surface.

[0030] The phrase ‘reinforced cement concrete’ or ‘RCC’ can be used interchangeably, as known to a person of ordinary skill in the art, refers to blend of concrete that has essentially the same ingredients as conventional concrete but in different ratios, and increasingly with partial substitution of fly ash for Portland cement. The RCC possesses high tensile strength.

[0031] The term ‘putty’, as known to a person of ordinary skill in the art, refers to a material with high plasticity, similar in texture to clay or dough, typically used in constructions and repair as a sealant or filler. Conventionally, wall putty is applied on walls, right after their construction is complete with bricks and sand-cement plaster, which helps in smoothing out the wall surface and making it easier to apply a coat of primer and then paint on the walls.

[0032] The term ‘primer’, as known to a person of ordinary skill in the art, refers to a precoating applied on the surface to prepare it for the subsequent process of finishing. It is a product like paint but is not a final finish, as it only protects the surface and acts as a support for a better paint adhesion.

[0033] The present application provides a gypsum plaster composition. In accordance with one aspect of the present disclosure the gypsum plaster composition comprises 25 to 75 % of stucco; 25 to 75 % of filler; 0.005 to 0.1 % of retarder; 0.01 to 0.1 % of heat resistant accelerator; 0.05 to 0.5 % of modified cellulose ether; 0.05 to 3 % of redispersible polymer and 0 to 0.5% of coloring agent. Beneficially, such a composition has exhibited enhanced, direct adhesion on a reinforced cement concrete surface. Further, beneficially, such a gypsum plaster composition also possesses faster curing or setting time, low volume loss to abrasion and enhanced coverage for the same thickness.

[0034] The present inventors have unexpectedly realized that the additives including modified cellulose ether and the re-dispersible polymer can be used in combination with base stucco composition, which when further applied on an RCC surface not only improved the direct adhesion but achieved undulated free coating. Further, beneficially the inventors have also realized that with the addition of the aforesaid additives, the gypsum slurry composition avoids the additional need of application of putty and / or primer. Furthermore, the gypsum slurry composition avoids the additional need of application of paint, as the case may be. In accordance with the present invention, the stucco is present in an amount ranging from 25 to 75 wt% of the composition. In a preferred embodiment, the stucco is present in the range of 25 to 50 wt%. In a most preferred embodiment, the stucco is present in an amount of 25 - 40% by weight. As is known in the art, the stucco can have a variety of compositions, depending on the source and the application at hand. As per the present invention, the stucco is a white cementing material made by partial or complete dehydration of the mineral gypsum. It is an environmentally friendly alternative to traditional sand-cement application for internal plastering surfaces.

[0035] The stucco in accordance with the present invention, provides excellent thermal and acoustic properties while providing superior rich and smooth finish, when used in combination with the modifiers and / or additives. Gypsum plastering is also a faster application method for internal surfaces, since it does not require time consuming water curing process. While water curing process is mandatory for 20 to 21 days after sandcement plastering to reduce shrinkage cracks arising due to heat of hydration. The gypsum plaster composition in accordance with the present invention cures in less than 1 hour. In some embodiments, the gypsum plaster in accordance with the present invention cures in less than 6 hours including final coat. In a most preferred embodiment of the present invention, the gypsum plaster cures in less than 45 minutes.

[0036] The gypsum plaster composition comprises a filler, in accordance with the present invention, ranging in an amount of 25 to 75 %. In a preferred embodiment, the filler is present in an amount of 50 to 75%. The filler provides desired coverage and water retention property to gypsum. In an embodiment the weight ratio of stucco to filler is no more than 30:70. In accordance with the present disclosure, weight of stucco is no less than 25% and weight of filler is no more than 75%. The filler in accordance with the present invention has a particle size ranging from 10 to 150 microns. The gypsum plaster composition in accordance with the present invention, may also further comprise one or more accelerators, retarders, fluidizers, coloring agents, dispersants, foaming agents, and / or glass fibers. In some embodiment the aforesaid agents are present in an amount of no more than 2.0 weight % of the gypsum plaster composition. In various embodiments the aforesaid agents are present in an amount of no more than 1.0 % or no more than 0.5 % by weight of the gypsum plaster composition. A person of ordinary skill in the art will use an appropriate set of the aforesaid agents for the desired gypsum slurry composition.

[0037] A combined cellulose ether and re-dispersible polymer in accordance with the present disclosure is in the range of 0.6 to 1.75%. In most preferred embodiment, the amount is in the range of 1 to 1.5%.

[0038] In a specific embodiment, the retarder is present in an amount ranging from 0.005 to 0.15 % and is selected from the group consisting of organic admixtures such as tartaric acid and its salts, citric acid, phosphates, protein and any composite. In a most preferred embodiment, the retarder is present in an amount of 0.005% to 0.1% and is used to extend / delay the setting time of gypsum by slowing the rate of crystal formation, hence, providing enough time for mixing and application of the plaster for desired substrate. In a specific embodiment, the retarder is citric acid.

[0039] In a specific embodiment, the heat resistant accelerator is present in an amount ranging from 0.01 to 0.1 % and is selected from the group consisting of calcium sulphate dihydrate, potassium sulphate, magnesium oxide or a combination thereof. In a most preferred embodiment, the heat resistant accelerator is calcium sulphate dihydrate coated with sucrose which is present in an amount of 0.025 to 0.1%. The heat resistant accelerator in every embodiment is required for providing nucleation sites for and increasing the rate of gypsum crystal growth. The inventors in accordance with the present disclosure have avoided the use of paint by introducing a coloring agent in an amount ranging up to 1 %. In a preferred embodiment, the coloring agent is present in an amount ranging from 0.1 to 1% and is selected from the group consisting of non-ionic surfactant, iron oxide yellow, pyrazol, butanamide, chromium oxide, azo and phenylene compounds. In a most preferred embodiment, the coloring agent is present in less than 0.75 wt% and is an aqueous dispersible agent. In an alternate embodiment, the gypsum plaster composition can also be devoid of coloring agent, as preferred by the end customers. The gypsum plaster composition without coloring agent gives a white color.

[0040] In every embodiment of the present invention, the modified cellulose ether is present in the range of 0.05 to 0.5 % by weight of the gypsum plaster composition. In a preferred embodiment the modified cellulose ether is present in the range of 0.05 to 0.3%. In a most preferred embodiment, the modified cellulose ether is present in an amount of 0.1 to 0.25% by weight of the gypsum plaster composition. The modified cellulose ether in accordance with the present invention is selected from the group consisting of hydroxypropyl methyl cellulose; hydroxyethyl methyl cellulose, starch, cellulose ether, modified cellulose ether, guar gum, dextrose, or a combination thereof. In a preferred embodiment, the modified cellulose ether is a thickener as well as a water retention agent improving the workability & viscosity of gypsum plaster.

[0041] In every embodiment of the present invention, the re-dispersible polymer is present in the range of 0.5 to 3% by weight of the gypsum plaster composition. In a preferred embodiment the re-dispersible polymer is present in the range of 0.5 to 2%. In a most preferred embodiment, the re-dispersible polymer is present in an amount of 0.5 to 1.5% by weight of the gypsum plaster composition. The re-dispersible polymer in accordance with the present invention is selected from the group consisting of PVAc, PVA, EVA or a combination thereof. In a preferred embodiment, the re-dispersible polymer is a copolymer of EV Ac. The cellulose ethers provide good water retention, prevents chalking and the re-dispersible polymers (being neutral) aids bonding with RCC substrate. The re-dispersible polymer in accordance with the present invention also improves the workability and enhances the mechanical properties including tensile, flexural strength and abrasion resistance of the coated RCC substrate.

[0042] In every embodiment of the present invention, the adhesion strength of the coating applied onto the surface is 0.2 to 1.5 MPa. In a preferred embodiment, the adhesion strength of the coating applied onto the surface is 0.25 MPa.

[0043] In accordance with an embodiment, of the present invention the re-dispersible polymer has a particle size ranging from 50 to 100 microns. In a preferred embodiment, the redispersible polymer has a particle size of 60 to 80 microns. In another embodiment, the re-dispersible polymer has a density in the range of 490 -590 kg / m3.

[0044] Inclusion of the additives like modified cellulose ether and re-dispersible polymer has not only improved the adhesion of the composition but also enables to provide a direct single / monolayer on the RCC surface to achieve a thickness of less than 6 mm. With the existing Mivan technology, thickness dropped from 12 mm to 6mm as maximum Plastering requirement. Over which wall putty and standard levelling gypsum plaster cannot withstand at such lower thickness due to poor water retention property which in turn leads to crack and delamination. Hence, an additional layer of bonding agent on RCC for improved adhesion of gypsum plaster is required (if a conventional Mivan technology is used) and over which finishing is performed with a primer followed by a paint. In accordance with the present invention, the gypsum plaster composition achieves a thickness build-up of less than 6mm in one coat application. Also, the curing and drying time is less than 24 hours for ex., less than 45 minutes, and more than 30 minutes. The gypsum plaster in an embodiment can be applied directly on RCC substrate, without requirement of a bonding agent. The gypsum plaster in accordance with the present invention, facilitates direct application of paint (based on customer requirement) on product without additional primer usage. In another embodiment, paint application can also be avoided as the gypsum plaster is also inclusive of the coloring agent, which imparts color to the applied plaster. Here, the gypsum plaster applicator is upskilled to apply gypsum finishing plaster, thereby increasing productivity, repeatability, and reduced low labor cost.

[0045] In an embodiment, the pH of the gypsum plaster composition is in the range of 6.5 to 7.5. In a preferred embodiment, the pH is neutral. The pH of the gypsum plaster is important as it has a correlation to the strength of plaster, especially, compressive strength. A negative influence is observed as pH increases. Generally, the application of the plaster is done manually by hand, hence maintaining a neutral pH also makes the application user friendly.

[0046] The present application also discloses a method of manufacturing a gypsum plaster composition. The method comprises the steps of mixing the stucco, filler, retarder, heat resistant accelerator, modified cellulose ether, re-dispersible polymer and coloring agent until a uniform, homogeneous dry mix is formed. Further added to the dry mix is water (here 40-50wt.% of dry plaster), to form a lump-free consistent slurry.

[0047] The present invention discloses a method of applying gypsum plaster composition on a reinforced cement concrete surface. The method comprises the steps of coating the already pre-wetted surface of the RCC substrate with the gypsum plaster slurry. The applied coating is troweled to smoothen the coat. Further, optionally a diluted coat of less than 1 mm is applied before set within the setting time of plaster. In an embodiment of the present invention, the formed mixture of gypsum plaster is applied as a single coat layer or as a monolayer or as a dual coat on the RCC surface. In a most preferred embodiment of the present invention, the formed mixture of gypsum plaster is applied as a single coat layer or as a monolayer on the RCC surface. The method avoids a further application of putty, primer and paint. The gypsum plaster applied on the RCC substrate, in accordance with the present invention has an adhesion strength ranging from 0.2 to 0.3 MPa.

[0048] The method further comprises the steps of coating the lump-free slurry of the present invention over the surface of reinforced cement concrete. The applied monolayer of the gypsum plaster is further troweled to smoothen the coat. The coat is allowed to cure and set in less than 60 minutes. In a preferred embodiment the gypsum plaster finish coat is cured in as less than 30 to 45 minutes. In some embodiments, the monolayer of the gypsum plaster finish coat can further optionally be provided with a diluted coat of less than 1 mm.

[0049] The gypsum plaster composition produced in accordance with the present disclosure, lias improved coverage, similar adhesion as gypsum plaster and compression strength like putty onto a RCC surface. Preferably such a gypsum plaster finds it application in buildings, ceiling and common areas including parking lots, staircase underlayment and basement.

[0050] EXAMPLES

[0051] Inventive Example 1

[0052] Table 1 discloses a gypsum plaster composition, according to an inventive Example 1. It is to be noted here that total composition percentage is based on a combination of dry stucco and dolomite. Table 1

[0053] Comparative Example 1

[0054] As a comparative example 1, putty sample of commercially available JK Cement Wallmaxx has been used. Commercially available JK Cement Wallmaxx putty sample usually comprises of

[0055] • White Cement,

[0056] • Fine Graded Fillers,

[0057] • Re-dispersible Polymer powder and

[0058] • Performance enhancing Additives

[0059] Comparative Example 2 As a comparative example 2, putty sample of commercially available Asian Paints Trucare has been used. Commercially available Asian Paints Trucare putty sample usually is:

[0060] • a white cement-based product with re-dispersible polymer and functional additives for application on interior and exterior rough plasters

[0061] Comparative Example 3

[0062] As a comparative example 3, putty sample of commercially available Birla white Wallcare has been used. Commercially available Birla white Wallcare putty sample usually is:

[0063] • Birla White Cement, Extra Hydrophobic Polymers, and some special chemicals and mineral fillers

[0064] Preparation of gypsum plaster composition as per the Inventive Example 1 :

[0065] The plaster was prepared by mixing the dry ingredients in a planetary mixer for 10 min. The minor additives were weighed on a calibrated weighing scale to nearest 0.01 g and added to the mixer containing the major ingredients stucco and dolomite. Post dry- mixing for 10 min, the homogenous mix is bagged in moisture-proof lined PE bags. Each bag weighs up to 40kg.

[0066] The following tests have been performed for the gypsum plaster as per the inventive example over the comparative examples 1 to 3 to evaluate the claimed performance. a) Tensile Adhesion Strength:

[0067] In accordance with Standard: EN 1015-12; EN 13279

[0068] The TAS is tested using a standardized and hand-held pull-off tester from Aimil Ltd. The load rate is set to 200N / s and the results are calculated in MPa. Table 2 b) Compression Strength:

[0069] In accordance with Standard: IS 516:1959

[0070] The CS is tested using a standardized UTM tester or a compression tester from AIMIL Ltd. Here, the load rate is 2.9kN / s and the results are calculated in MPa.

[0071] Table 3

[0072] It is inferred that compressive strength of the samples as per the comparative examples 1 to 3 matches their claim of 3-7 MPa, while the strength of gypsum plaster at 45% water gauge is ~ 3MPa equivalent to 14-day strength of competitor putty samples. This can be attributed to the presence of gypsum crystals that resist crack propagation and equilibrate the compressive stress cracks. At times walls plastered with cement [comparative example 1 to 3 samples] tend to develop cracks or shrinkage after a few months, but gypsum plaster as per the inventive example 1, remains fault-free for a longer time, due to the presence of gypsum crystals. In accordance with the inventive example 1, the cement of comp examples is replaced by stucco as a binder contributing to high strength. c) Abrasion Resistance:

[0073] In accordance with Standard: ASTM D2486- 17

[0074] The AR is tested using a standardized Abrasion tester from Elcometer. The test protocol follows for 50 cycles; Speed: 65 cycles / min and failure mode are determined as no. of cycles until complete material removal. The final calculation is volume loss in cm3.

[0075] Table 4

[0076] It is indicated from the above table 4 that Inventive Example 1 has low material volume loss which corresponds to less chalking of material on the site and the improved interparticle bonding in the material. Indeed, the number of cycle to failure is similar to comparative example 3, but with a lower volume loss (15 cm3for invention vs 21 cm3for comparative example 3). d) Paintability:

[0077] Table 5 e) Moisture property - Capillary Water absorption co-efficient

[0078] In accordance with standard BS EN 1015-18

[0079] The inventive and comparative coated samples were cut into two equal halves, thereafter, immersed in water up to a height of 5- 10mm. As the core encounters water, absorption of water due to capillary action results in increase in weight. This gravimetric change was noted to quantify the moisture resistance. Coefficient of water absorption has been calculated using the below formula.

[0080] C = 0.03* (Ml -MO) (kg / (m2. min0.5)) where,

[0081] Ml - weight gain after 10 minutes (g)

[0082] MO - initial weight (g)

[0083] The mean of the individual half-specimens was calculated as mean coefficient of water absorption due to capillary action (Cm) stated to the nearest 0.1 kg / (m2. min0.5).

[0084] The sample as per the inventive example 1 showed an absorption coefficient between 0.028 and 0.045 which is well below the standard limit of 0.1 kg / m2min°5..

[0085] Note that not all of the activities described above in the general description, or the examples are required, that a portion of a specific activity may not be required, and that one or more further activities may be performed in addition to those described.

[0086] Benefits, other advantages, and solutions to problems have been described above about specific embodiments. However, the benefits, advantages, solutions to problems, and any feature(s) that may cause any benefit, advantage, or solution to occur or become more pronounced are not to be construed as a critical, required, or essential feature of any or all the claims.

[0087] The specification and illustrations of the embodiments described herein are intended to provide a general understanding of the structure of the various embodiments. The specification and illustrations are not intended to serve as an exhaustive and comprehensive description of all of the elements and features of apparatus and systems that use the structures or methods described herein. Certain features, that are for clarity, described herein in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features that are, for brevity, described in the context of a single embodiment, may also be provided separately or in a sub combination. Further, reference to values stated in ranges includes each and every value within that range. Many other embodiments may be apparent to skilled artisans only after reading this specification. Other embodiments may be used and derived from the disclosure, such that a structural substitution, logical substitution, or another change may be made without departing from the scope of the disclosure. Accordingly, the disclosure is to be regarded as illustrative rather than restrictive.

[0088] The description in combination with the figures is provided to assist in understanding the teachings disclosed herein, is provided to assist in describing the teachings, and should not be interpreted as a limitation on the scope or applicability of the teachings. However, other teachings can certainly be used in this application.

[0089] As used herein, the terms "comprises," "comprising," "includes," "including," "has," "having" or any other variation thereof, are intended to cover a non-exclusive inclusion.

[0090] Also, the use of "a" or "an" is employed to describe elements and components described herein. This is done merely for convenience and to give a general sense of the scope of the invention. This description should be read to include one or at least one and the singular also includes the plural, or vice versa, unless it is clear that it is meant otherwise. For example, when a single item is described herein, more than one item may be used in place of a single item. Similarly, where more than one item is described herein, a single item may be substituted for that more than one item.

[0091] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The materials, methods, and examples are illustrative only and not intended to be limiting. To the extent that certain details regarding specific materials and processing acts are not described, such details may include conventional approaches, which may be found in reference books and other sources within the manufacturing arts.

[0092] While aspects of the present disclosure have been particularly shown and described with reference to the embodiments above, it will be understood by those skilled in the art that various additional embodiments may be contemplated by the modification of the disclosed machines, systems and methods without departing from the spirit and scope of what is disclosed. Such embodiments should be understood to fall within the scope of the present disclosure as determined based upon the claims and any equivalents thereof. 1

Claims

We Claim:1) A gypsum plaster composition or dry mix comprising, by weight:25 to 75 % of stucco;25 to 75 % of filler;0.005 to 0.1 % of retarder;0.01 to 0.1 % of heat resistant accelerator;0.05 to 0.5 % of modified cellulose ether;0.05 to 3 % of re-dispersible polymer; and 0 to 1 % of coloring agent.2) The gypsum plaster composition as claimed in claim 1, wherein the modified cellulose ether is selected from the group consisting of hydroxypropyl methyl cellulose; hydroxyethyl methyl cellulose, methylhydroxypropyl cellulose, hydroxyethyl cellulose, hydrophobically modified hydroxyethyl cellulose or a combination thereof.3) The gypsum plaster composition as claimed in claim 1 , wherein the filler is selected from the group consisting of calcium magnesium carbonate.4) The gypsum plaster composition as claimed in claim 1, wherein the ratio of stucco to filler is in the range of 30:70.5) The gypsum plaster composition comprising the gypsum plaster composition or dry mix as claimed in claim 1, and further comprising water in such that the ratio of dry mix ingredients to water is in the range of 40:60 to 40:50.6) The gypsum plaster composition as claimed in claim 5, is a wet gypsum plaster composition.7) The gypsum plaster composition as claimed in claim 6, wherein the wet gypsum plaster is applied on a reinforced cement concrete surface as a monolayer and has improved direct adhesion on the reinforced cement concrete surface.8) The gypsum plaster composition as claimed in claim 6, wherein pH of the composition is in the range of 6.5 to 7.5.9) The gypsum plaster composition as claimed in claim 7, avoids the application of a base coating on the surface.10) The gypsum plaster composition as claimed in claim 7, wherein the curing time of the coating applied onto the substrate is less than 45 minutes.11) The gypsum plaster composition as claimed in claim 7, wherein the thickness of the coating applied onto the substrate is 2 to 6 mm.12) The gypsum plaster composition as claimed in claim 1, wherein the retarder is selected from the group consisting of citric acid, tartaric acid and its salts, phosphates, protein and any composite thereof.13) The gypsum plaster composition as claimed in claim 1, wherein the heat resistant accelerator is selected from the group consisting of calcium sulphate dihydrate, potassium sulphate, magnesium oxide or a combination thereof.14) The gypsum plaster composition as claimed in claim 1, wherein the re-dispersible polymer is selected from the group consisting of polyvinyl acetate, Ethylene vinyl acetate, polyvinyl alcohol, or a combination thereof.15) The gypsum plaster composition as claimed in claim 1, wherein the coloring agent imparts color including but not limited to orange, yellow, pink, green, brown.16) The gypsum plaster composition as claimed in claim 1, wherein the coloring agent is selected form the group consisting of non-ionic surfactants, iron oxide yellow, pyrazol, butanamide, chromium oxide, azo and phenylene compounds or a combination thereof.17) The gypsum plaster composition as claimed in claim 1, wherein the composition further comprises thickener, whitening agents, fillers.18) The gypsum plaster composition as claimed in claim 1 , wherein the re-dispersible polymer has a particle size ranging from 50 to 100 microns.19) The gypsum plaster composition as claimed in claim 1, wherein the stucco has a particle size ranging from 40 to 50 microns.20) The gypsum plaster composition as claimed in claim 1, wherein the filler has a particle size ranging from 50 to 150 microns.21) The gypsum plaster composition as claimed in claim 7, wherein the adhesion strength of the coating applied onto the surface is between 0.2 to 1.5 MPa.22) The gypsum plaster composition as claimed in claim 7, wherein the compression strength of the coating applied onto the surface is between 1 to 3 MPa.23) A method of manufacturing a gypsum plaster composition, the method comprising the steps of:a. mixing the stucco, filler, retarder, heat resistant accelerator, modified cellulose ether, re-dispersible polymer and coloring agent of the gypsum plaster composition as claimed in claim 1 ; and b. adding water to the gypsum plaster composition formed in step a, to form a lump-free consistent slurry.24) A method of applying gypsum plaster composition on a reinforced cement concrete a. coating the formed lump-free slurry of claim 23, on the surface of a reinforced cement concrete; b. troweling the gypsum plaster to smoothen; and c. optionally providing a diluted coat of less than 1 mm.

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