AU2011201333B2 - Coatings for building products - Google Patents

Abstract

Abstract A method for coating a building product in which a coating formulation is provided which includes an hydraulic binder and a quantity of dewatering agent. A slurry is produced from said formulation and applied to the product to be coated. The resultant 5 coating is then dewatered through said product. Dewatering can be accomplished with or without vacuum assistance. The method is suitable for producing a composite product which comprises a base structural layer with the coating thereon. )I

Description

- 1 AUSTRALIA PATENTS ACT 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT ORIGINAL Name of Applicant: James Hardie Technology Limited Actual Inventors: Basil Naji and Milton O'Chee Address for Service is: SHELSTON IP 60 Margaret Street Telephone No: (02) 9777 1111 SYDNEY NSW 2000 Facsimile No. (02) 9241 4666 CCN: 3710000352 Attorney Code: SW Invention Title: COATINGS FOR BUILDING PRODUCTS Details of Original Application No. 2008200439 dated 29 Jan 2008 The following statement is a full description of this invention, including the best method of performing it known to me/us: File: 34505AUP02 - la TITLE: COATINGS FOR BUILDING PRODUCTS Technical Field This application claims priority from the following Australian provisional patent applications, the full contents of which are hereby incorporated by cross-reference. 5 Application No Title Date Filed PR3474 A Composite Product 2 March 2001 PR3475 Spattering Apparatus 2 March 2001 PR3476 Additive for a Dewaterable Slurry 2 March 2001 PR3477 A Method and Apparatus for Forming a 2 March 2001 10 Laminated Sheet Material by Spattering PR3478 Coatings for Building Products 2 March 2001 The present invention relates to coatings and in particular coatings for building products and laminated building products. Background Art 15 Any discussion of the prior art throughout the specification should in no way be considered as an admission that such prior art is widely known or forms part of common general knowledge in the field. There are a huge variety of mechanisms for applying coatings to building products such as building boards. 20 The coatings can be divided into two main groups namely finishiiig coatings, which are intended primarily for aesthetic purposes, and functional coatings which provide some additional structural or other property/attribute to the resultant product. The application technique depends to a large extent on the properties of the coating composition and base layer or product to be coated. Manual application and 25 spraying etc are most popular but they restrict the types of coating to be applied and indeed the building product to be coated. For example, when using a spray technique, one must ensure the coating composition is of sufficient flowability to pass through the spray nozzle but at the same time, the base material to be coated must be sufficiently rigid to withstand the impact of the spray coating. 30 For certain building products, such as internal wall systems, a smooth surface finish is vital. Gypsum or plaster board is used almost exclusively as an internal wall board due to its excellent surface finish.

-2 The use of fibre reinforced cement building board for instance as an internal wall board has significant advantages including cost and structural integrity as compared with gypsum board. However, some techniques for production of fibre reinforced cement sheets do not provide a gypsum like surface finish. In response to 5 public demand, builders require an internal wall board with a near perfect surface I------------- --------- i - pUre finish. Even minUte irregulitiesMI wich arise fro p10 UU1roucution oir reniorced cement sheets can be sufficient to reject the product. Sanding the surface of the FRC sheet has been used to improve its surface finish but in some instances such sanding can 'feather' or leave exposed the reinforcing fibres thereby exacerbating the problem. 10 It is an object of the present invention to overcome or ameliorate at least one of the disadvantages of the prior art, or to provide a useful alternative. Disclosure of the Invention According to a first aspect, the present invention provides a dewatering aid for dewatering a cementitious slurry coating on a product, said dewatering aid comprising 15 a particulate material in an effective quantity and particle size to maintain porosity in the slurry and the product to be coated during dewatering and thereby permit dewatering of the slurry through the product to be coated, wherein said dewatering aid is fly ash particles having two components with a first larger size component of particles of about a 100 micron maximum size in an amount of about 10 to 60 wt % of 20 the cementitious slurry based on total dry ingredients, and a second smaller size component of particles of about a 10 micron maximum size in an amount of about 5 to 30 wt. % of the cementitious slurry based on total dry ingredients. According to a second aspect, the present invention provides a dewatering aid for dewatering a cementitious slurry coating on a product, said dewatering aid 25 comprising a particulate material in an effective quantity and particle size to maintain porosity in the slurry and the product to be coated during dewatering and thereby permit dewatering of the slurry through the product to be coated, wherein said dewatering aid comprises about 25-60 wt % silica, about 10-30 wt % A1 2 0 3 , about 5 25 wt % Fe 2

O

3 , about 0-20 wt % CaO, about 0-5 wt % MgO, wherein a first portion of 30 the particulate material has a larger particle size of about a 100 micron maximum size in the amount of about 10 to 60 wt % of the cementitious slurry based on total dry ingredients and a second portion of the particulate material that is a smaller particle -3 size of about a 10 micron maximum size in the amount of 5 to 30 wt. % of the formulation based on total dry ingredients, and wherein the slurry is up to 50% water, wherein the water is based on percent by total weight of solids. Unless the context clearly requires otherwise, throughout the description and the 5 claims, the words 'comprise', 'comprising', and the like are to be construed in an inciusivU snsie as opposed to an exclusive or exhaustive sense; that is to say, in the sense of "including, but not limited to". The dewatering agent serves to maintain sufficient porosity in the slurry and product to be coated to permit dewatering of the slurry through the product to be 10 coated. Preferably, the dewatering agent is a particulate material such as fly ash, alumina trihydrate, silica flour, cenospheres (ceramic hollow spheres) or similar. Fly ash is particularly preferred as it permits dewatering of the slurry within a few minutes. Other particulate dewatering agents such as alumina trihydrate or silica flour may also be used, however, they increase the time required for dewatering of the 15 slurry through the product to be coated. In a preferred embodiment, the slurry applied to the product to be coated has a high water content. Preferably, the water content can be up to 50%. This is in contrast to previous cementitious formulations which generally have a higher solids content. 20 By combining the various components of the coating formulation described above, a dewaterable slurry is obtained which can be applied to the building product, dewatered through the building product and thereby provide a uniform coating over the building product. Normally, after application of the coating, the resultant product would be 25 normally cured, steam cured or hydrothermally cured, ie autoclaved, and if required, sanded to a smooth flat finish. The building product to which the coating can be applied is virtually limitless provided the slurry can be dewatered through the building product. Cementitious and -4 gypsum building boards are typical examples of suitable building products on which the coating can be applied. The resultant coating, which may optionally contain fibres, results in a decorative finishing layer which is sandable, smooth, flat, low permeable, crack free 5 and/or flexible, ready to be finished, for example by painting. The thickness of such a coating layer prior to sanding would range from around 0.1 to 10 mm, preferably 0.5 to 5 mm and most preferably 1 to 3 mm. After sanding, the finish layer may have a depth of around 0.05 to 5 mm, preferably 0.1 to 2 mm and most preferably 0.5 to 1 mm. The thus produced coated 10 product is comparable in its workability to monolithic (single layer) composites. It can be flexed, cut, drilled and fixed by nails etc to a frame without surface cracking or chipping. The applicant's have found an extremely good interlaminer bond and compatibility between the dewatered slurry layer and base layer resulting in excellent 15 composite action, compatibility and resistance to delamination. The term 'hydraulic binder' as used throughout the specification refers to a pulverised material in the solid, dry state which, when mixed with water, yields plastic mixtures that are able to set and harden, for example a cement. Included within the ) definition are white, grey or pigmented cements and hydraulic limes. 20 The term 'cement' includes hydraulic and alite cements such as pirtland cement, blended cements such as portland cement blended with fly ash, blast-furnace slag, pozzalans and the like and mixtures thereof, masonry cement, oil well cement, natural cement, alumina cement, expansive cements and the like, or mixtures thereof -The quantity of binder in the formulation is preferably between 10 to 50 wt% 25 based on the total dry ingredients, more preferably 15 to 40 wt% and most preferably 20 to 30 wt%. The fly ash used in the present invention provides a number of advantages including, particularly, as an aid to dewatering of the slurry as defined above. The term 'fly ash' as used herein refers to a solid powder having a chemical 30 composition similar to or the same as the composition of material that is produced during combustion of powdered coal, ie 25 to 60 wt% silica, 10 to 30 wt% A1 2 0 3 , 5 to 25 wt% Fe 2

O

3 , 0 to 20 wt% CaO and 0 to 5 wt% MgO.

Fly ash particles are typically spherical and range in diameter from 1 to 100 microns. In a preferred embodiment, the fly ash comprises two components. A first 'larger' size particles of fly ash with preferably a 100 micron maximum size. This size range of fly ash is used in the slurry to aid in improving the dewatering characteristics 5 of the slurry but also as a moderately reactive pozzalan. The second 'smaller' fly ash size zone which preferably has a 10 micron maximum size also adds an improving dewatering characteristic but is a more highly reactive pozzalan. This 'smaller' fly ash particle zone also improves the sanded surface quality of the finish layer. 10 In a preferred embodiment, the first fly ash comprises 10 to 60 wt% of the formulation based on total dry ingredients, more preferably 20 to 50 wt% and most preferably 30 to 40 wt%. The second fly ash component preferably provides 5 to 30 wt% of the formulation based on total dry ingredients, more preferably 10 to 25 wt% and most 15 preferably 15 to 20%. In another preferred embodiment, the dewatering agent may include a coarse fraction fly ash which is greater than 100 microns. This coarse fraction fly ash includes bottom ash or similar products from coal combustion. There is an advantage to using these products over the aforementioned particle size fly ash since it is 20 cheaper. Of course, as will be clear to persons skilled in the art, some reformulation of the slurry may be required to provide a suitable coating and appropriate dewatering characteristics when the dewatering agent is such a coarse fraction fly ash. The coating may optionally contain other additives such as fillers. Such fillers may also be used to improve the dewatering characteristics of the slurry. For 25 example, cenospheres (hollow ceramic microspheres) diatomite, wollastonite, ground rice hulls, ground perlite or the lice, are particularly suitable for this purpose. These and other fillers may also be used to provide additional benefits, for example calcium carbonates or alumina hydrates improve sandability and flexibility of the coated layer respectively. Silica flour improves hardness of the sanded surface of 30 the coating layer and the acoustic/thermal insulation properties of the layer can be improved by including rubber particles, venicullt,perlite,~expanded polystyrene or gypsum.

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The fillers preferably comprise 5 to 30 wt% of the formulation based on total dry ingredients, more preferably 10 to 25 wt% and most preferably 25 to 20 wt%. The coating may also contain other organic additives. Cement plasticising agents, for example, may be used to alter the rheology of the slurry. Suitable cement 5 plasticising agents include melamine sulphonate formaldehyde condensates, naphthalene sulphonate formaldehyde condensates, naphthalene sulphonates, calcium lignosulphonates, sodium lignosulphonates, saccharose, sodium gluconate, sulphonic acids, carbohydrates, amino carboxylic acids, polyhydroxycarboxilic acids, sulphonated melomine and the like. 10 The amount of cement plasticiser of course will depend upon the fluidising ( ability of the particular plasticisers. Generally the quantity of plasticiser will be in the range of 0.3 to about 3 wt% and more preferably 0.5 to 2 wt% based on the total of dry ingredients in the formulation. Particularly preferred cement plasticisers are Melment F- 10, a melamine 15 formaldehyde sodium bisulphate polymer dispersant marketed by SKW-Trostburg in the form of a fine white powder. Another suitable plasticiser is Neosyn, a condensed sodium salt of sulphonated naphthalene formaldehyde available from Hodgson Chemicals. Another preferred component in the coating is a biopolymer which acts to 20 enhance the flowability, segregation resistance and self levelling qualities of the cementitious slurry. Particularly suitable bioplymers are xanathan gum and/or whelan gum, eg KELCO-CRETE, KIC 376 manufactured by Monsanto. Latex may also be included in the coating composition to improve adherence, elasticity, stability and impermeability of the coating. The latex also improves 25 flexibility of the formed coating. The latex may be selected from the group consisting of acrylic latex, styrene latex, butadiene latex or mixtures thereof and is provided preferably in an amount between 0.5 to 20%, more preferably I to 15% and most preferably about 10% by weight of cement (on polymer solids basis) solids. 30 Vinyl polymers may also be incorporated into the coating either in addition or as a substitute to the latex emulsions. Such vinyl polymers or equivalent polymeric -7 materials enhance adhesion, resilience and flexural strength and abrasion resistance of the coating. Preferred vinyl polymers include polyvinyl acetate or a copolymer vinyl acetate with another monomer such as ethylene. A particularly preferred vinyl acetate resin is 5 VINNAPAS LL5044 thermo plastic resin powder which contains a vinyl acetate ethylene copolymer available from Wacker. Such powdered vinyl polymer is preferably provided in quantities similar to the latex emulsion referred to above. ) In addition to the above, conventional other additives such as mineral oxides, hydroxides and clays, metal oxides and hydroxides, fire retardants such as magnesite, 10 thickeners, silica fume or amorphous silica, water sealing agents, water reducing agents, setting modifiers, hardeners, dispersants, foaming agents or flocculating agents, water-proofing agents and density modifiers are suitable for use with the present invention. In this regard, one particular advantage arising from the present invention is the 15 ability to treat the product to be coated by providing additives in the coating. To explain, since the coating is dewatered through the product to be coated, it is possible to provide additives to the base layer by incorporation in the slurry. For instance, a waterproofing agent such as silane may be included in the coating in excess of the ) coating layers requirements. During dewatering, the silane will be drawn into and 20 through the base layer being coated thereby treating the base layer. This simultaneous treatment of the base layer as well as coating the base layer is a valuable additional benefit arising from the aforedescribed method. Best Mode for Carrying Out the Invention The present invention will now be described by way of example only with 25 reference to the following embodiments. In each of the following examples, the product was produces as follows. Step 1 Slurry preparation A slurry of the formulation is prepared by mixing the hydraulic binder, fly ash and other optional components with water. The solids content in the slurry is 30 preferably between 50 and 90%, more preferably 55 to 80% and most preferably 60 to 70%.

Step 2 Slurry application/dewatering The slurry is applied to the base layer by any convenient means such as brushes rollers, knives or sprays etc. In a particular embodiment the slurry is applied by means of the apparatus and method subject of Australian Provisional Patent 5 Application Nos. PR3475 and PR3477, which are incorporated herein by reference. The slurry is preferably designed to self level and form a uniform coating on the product. The building product to be coated exhibits s certain degree of porosity ) causing the slurry to dewater and form a uniform deposited cementitious layer. Time for dewatering can vary quite dramatically but normally occurs between 10 and 10 90 seconds, depending on the porosity of the material to be coated, its water content and thickness and viscosity of the slurry formulation. A vacuum may be used to reduce the slurry dewatering time if required. This is particularly useful when tailoring the coating process to the speed of a building product forming process, eg between 40 to 45 seconds on a Hatschek production line. 15 Step 3 Curing After forming, the green laminate article comprising the building product plus coating is preferably precured for a short time, eg up to 48 hours, then cured by air/moist curing at room temperature, steam curing between 40 and 90"C or autoclaving in a steam pressure vessel between 120 and 200*C. 20 For either of these three curing techniques, a curing time range between 6 and 72 hours, preferably up to 48 hours, is suitable. Of course, as will be clear to persons skilled in the art, the length of time chosen for curing is dependent on the formulation, the manufacturing process and form of the article. The following examples relate to specific formulation compositions. 25 Example 1: Sandable Dewatered Slurry Composition Function: sandable, durable finishing layer for facade applications. The low viscosity slurry (drainage time in 50 ml volume funnel= 3.4 seconds) was applied on the base layer (HardiformTM 12 nm thick cellulose fibre reinforced cement-based green sheet manufactured by James Hardie Industries). The slurry 30 dewatered in 90 seconds (un-aided by vacuum) forming a 1.25 mm thick coating. The coated sheet was autoclave-cured for 8 hrs at 180 *C temperature and 0.80 MPa -9 pressure. It was then sanded flat to 0.60 mm thick using industrial sanders equipped with 100 grit sand paper belts.

)I

- 10 Slurry % by total Weight in gm Composition weight of solids (S) Dewatered Cementitous Composition Portland Cement 30 12000 Silica Flour (400 G 10 4000 grade) Fly ash (larger size 40 16000 fraction) Fly ash (smaller size 20 8000 fraction) Total 100 40000 Water (W) 14000 Water/ Solids (W/S 0.35 ratio) Solids Content 0.74 (W/W+S) Organic Additives Welan Gum 0.0075 3.0 (Kelcocrete) naphthalene 0.25 100.0 formaldehyde Plasticising Agent (Neosyn) Acrylic Emulsion 1.0 400.0 Rhoplex MC1934 Example 2: Rubberised Dewatered Slurry Composition Function: Finishing layer in skid-resistant flooring, hard wearing static 5 dissipative flooring and acoustic insulating ceiling panels. The low viscosity slurry (drainage time in 50 ml volume funnel = 4.2 seconds) was applied on the base layer (HardifornrM 12 mm thick cellulose fibre reinforced cement-based green sheet manufactured by James Hardie Industries). The slurry dewatered in 60 seconds (un-aided by vacuum) forming a 1.25 mm thick coating. The 10 coated sheet was autoclave-cured for 8 lrs at 180 'C temperature and 0.80 MPa pressure. It was then sanded flat to 0.60 mm thick using industrial sanders equipped with 100 grit sand paper belts.

-- 11 Slurry % by total Weight in gm Composition weight of solids (S) Dewatered Cementitous Composition Portland Cement 30 12000 Recycled Rubber crumbs 10 4000 (minus 30 mesh) Fly ash (larger size 40 16000 fraction) Fly ash (smaller size 20 8000 fraction) Total 100 40000 Water 13000 Water/ Solids (W/S 0.325 ratio) Solids Content 0.755 (W/W+S) Organic Additives Welan Gum (Kelcocrete) 0.0075 3.0 naphthalene 0.25 100.0 fonnaldehyde Plasticising Agent (Neosyn) Acrylic Emulsion 1.0 400.0 Rhoplex MC1934 Example 3: Flexible & Sandable Dewatered Slurry Composition 5 Function: Flexible & sandable finishing layer on thin fibre cement reinforced cement-based lining. The low viscosity slurry (drainage time in 50 ml volume funnel =2.8 seconds) was applied on the base layer (HardiflexTM 4.5 mm thick cellulose fibre reinforced cement based green sheet manufactured by James Hardie Industries). The slurry dewatered in 10 120 seconds (un-aided by vacuum) forming a 1.25 mnn thick coating. The coated sheet was precured for 48 hours then was autoclave-cured for 8 hrs at 180 *C temperature and 0.80 MPa pressure. It was then sanded flat to 0.60 1mm thick using industrial sanders equipped with 100 grit sand paper belts.

-12 Slurry % by total Weight in gm Composition weight of solids (S) Dewatered Cementitous Composition Portland Cement 20 8000 Calcium Carbonate 10 4000 Grade 10 (40um avg. size) Alumina Tri-hydrate 5 2000 (80 urn avg. size) Fly ash (larger size 45 18000 fraction) Fly ash (smaller size 20 8000 fraction) Total 100 40000 Water 12000 Water/ Solids (W/S 0.30 ratio) Solids Content 0.77 (W/W+S) Organic Additive Welan Gum (Kelcocrete) 0.0075 3.0 naphthalene 0.25 100.0 formaldehyde Plasticising Agent (Neosyn) Styrene Acrylic Latex 5 2000 Emulsion (56% solids) Example 4: Flexible & Sandable Dewatered Slurry Composition (Low Cement) Function: Flexible & sandable finishing layer on thin fibre cement reinforced 5 cement-based lining. The low viscosity slurry (drainage time in 50 ml volume funnel = 4.5 seconds) was applied on the base layer (HardiflexTM 4.5 mm thick cellulose fibre reinforced cement-based green sheet manufactured by James Hardie Industries). The slurry dewatered in 90 seconds (un-aided by vacuum) forming a 1.25 mm thick coating. The 10 .coated sheet was autoclave-cured for 8 hrs at 180 *C temperature and 0.80 Mla -13 pressure. It was then sanded flat to 0.60 mm thick using industrial sanders equipped with 100 grit sand paper belts. Slurry % by Weight in gm Composition total weight of solids (S) Dewatered Cementitous Co position Portland Cement 10 4000 Calcium Carbonate 20 8000 Grade 10 (40um avg. size) Alumina Tri-hydrate 5 2000 (80 um avg. size) Fly ash (larger size 40 18000 fraction) Fly ash (smaller size 25 10000 fraction) Total 100 40000 Water 16000 Water/ Solids (W/S 0.40 ratio) Solids Content 0.715 (W/W+S) Organic Additives Welan Gum (Kelcocrete) 0.0075 3.0 naphthalene 0.25 100.0 formaldehyde Plasticising Agent (Neosyn) Vinyl acetate-ethylene 1.625 650 powdered copolymer (Vinnapas LL5004) 5 The aforementioned examples provide a coated product comparable in workability to monolithic or single layer composites. They can be flexed, cut, drilled or fixed by nails or the like to a frame without surface cracking or chipping. The surface is 'finish-ready' and remains smooth, flat, crack-free and with low permeability even when used in a curved configuration. 10 Each examples provided excellent interlaminer bond between the base sheet and coating exhibiting good composite action, compatibility and resistance to delamination.

-14 It can be seen that the present process provides a significant improvement not only in the attributes of the product but also in the ability to tailor the surface finish of a building product to match particular requirements. Examples of particular formulations to provide the desired finish characteristic include 5 a) Terrazzo (hardwearing decorative finish) - the finishing layer of the dewatered slurry can contain marble chips and pigmented cements and fillers. It may then be sanded and polished to form a hardwearing decorative finish. Such a coating on, for example, a fibre cement backing board, could be used as flooring tiles, decorative wall lining or external prefinished fibre cement cladding. 10 b) Stucco (orange peel) Finish -this may be achieved by manipulating speed and volume of the applied slurry to achieve a stucco look on the finishing layer. Once again, such a product may be used as an external pre-fmished cement cladding. c) Sandable finish - this is probably the simplest and most straightforward application of the coating technique to provide a coating layer which may be sanded 15 and sealed, thereby providing a paint ready smooth, crack-free and low permeable surface. Such a product may be used for a variety of internal and external uses. d) Flexible finish - the coating layer may include v- ious fillers and other additives to improve its flexibility, eg ethylene vinyl acetate, styrene butadiene rubber, styrene acrylic. It is designed to be a sandable, workable ie by score and snap, 20 nailable, crack-free, non-chipping, flexible and bendable, paint ready siface. Such a coating could normally be applied to reasonably thin building product to permit flexibility. It has a wide variety of uses but is particularly suitable as an internal lining in wet area applications or as an external cladding element, eg as a paint ready fibre cement siding. 25 e) Skim-coated finish - such a coating of the dewatered slurry may be applied to gypsum based building products thereby providing a smooth, flat, pre-skim coated and paint ready surface. f) Rubberised finish - by the addition of rubber crumbs into the slurry formulation, a coating layer may be provided on say a fibre cement backing for use as 30 a skid resistant flooring, hardwearing static dissipative flooring or acoustic insulating ceiling panels.

- 15 It will be understood by persons skilled in the art that the present invention may be embodied in other forms without departing form the spirit or scope of the inventive idea as described herein. In particular, it will be appreciated that the formulations, coatings, additives, methods and composite products of the present invention are 5 suitable or may be adapted for use in conjunction with the methods and apparatus as described in the various priority documents.

Claims (20)

1. A dewatering aid for dewatering a cementitious slurry coating on a product, said dewatering aid comprising a particulate material in an effective quantity and particle size to maintain porosity in the slurry and the product to be coated 5 during dewatering and thereby permit dewatering of the slurry through the product to be coated, wherein said dewatering aid is fly ash particles having two components with a first larger size component of particles of about a 100 micron maximum size in an amount of about 10 to 60 wt % of the cementitious slurry based on total dry ingredients, and a second smaller size 10 component of particles of about a 10 micron maximum size in an amount of about 5 to 30 wt. % of the cementitious slurry based on total dry ingredients.

2. The dewatering aid according to claim 1, wherein the slurry includes additives as fillers selected from the group consisting of ceramic hollow spheres, 15 diatomite, wollastonite, ground rice hulls, perlite, vermiculite, expanded polystyrene, gypsum, calcium carbonate, alumina hydrate, and silica flour.

3. The dewatering aid according to claim I or claim 2, wherein the product through which the slurry is dewatered is a cementitious building board or 20 product or gypsum building board.

4. The dewatering aid according to any one of the preceding claims, wherein the slurry includes fibres. 25

5. The dewatering aid according to any one of the preceding claims, wherein the coating includes an hydraulic binder selected from the group consisting of white, grey or pigmented cements, hydraulic limes and mixtures thereof

6. The dewatering aid according to any one of the preceding claims, wherein the 30 coating includes cements selected from the group consisting of Portland cement, blended cements, blast furnace slag, pozzolans, masonry cement, oil well cement, natural cement, alumina cement, expansive cements and - 17. mixtures thereof

7. The dewatering aid according to any one of the preceding claims, wherein the slurry includes a binder between about 10 and 50 wt % based on total dry 5 ingredients.

8. The dewatering aid according to any one of the preceding claims, wherein the slurry includes organic additives selected from the group consisting of plasticising agents and biopolymers. 10

9. The dewatering aid according to any one of the preceding claims, wherein the dewatering aid allows the coating to be uniform on the product.

10. The dewatering aid according to any one of the preceding claims, wherein the 15 dewatering aid permits dewatering of the slurry within a few minutes.

11. The dewatering aid according to any one of the preceding claims, wherein the cementitious slurry coating includes additives to improve resultant properties of the coating. 20

12. The dewatering aid according to any one of the preceding claims, wherein the cementitious slurry coating includes additives to improve workability and applicability of the slurry to the product to be coated. 25

13. The dewatering aid according to any one of the preceding claims, wherein the cementitious slurry coating includes additives to improve the properties of the product to be coated such that upon dewatering of the slurry through the product, the product is thus treated with said additive. 30

14. A dewatering aid for dewatering a cementitious slurry coating on a product, said dewatering aid comprising a particulate material in an effective quantity and particle size to maintain porosity in the slurry and the product to be coated - 18. during dewatering and thereby permit dewatering of the slurry through the product to be coated, wherein said dewatering aid comprises about 25-60 wt % silica, about 10-30 wt % A1 2 0 3 , about 5-25 wt % Fe 2 O 3 , about 0-20 wt % CaO, about 0-5 wt % MgO, wherein a first portion of the particulate material 5 has a larger particle size of about a 100 micron maximum size in the amount of about 10 to 60 wt % of the cementitious slurry based on total dry ingredients and a second portion of the particulate material that is a smaller particle size of about a 10 micron maximum size in the amount of 5 to 30 wt. % of the formulation based on total dry ingredients, and wherein the slurry is 10 up to 50% water, wherein the water is based on percent by total weight of solids.

15. The dewatering aid according to claim 14, wherein the dewatering aid is fly ash. 15

16. The dewatering aid according to claim 14 or claim 15, wherein the product through which the slurry is dewatered is a cementitious building board or product or gypsum building board. 20

17. The dewatering aid according to any one of claims 14 to 16, wherein the dewatering aid permits dewatering of the slurry within a few minutes.

18. The dewatering aid according to any one of claims 14 to 17, wherein the particulate material includes a particle size greater than about 100 microns 25 and wherein the particles of size greater than about 100 microns is selected from the group consisting of fly ash, and bottom ash.

19. The dewatering aid according to any one of claims 14 to 18, wherein the slurry includes additives as fillers selected from the group consisting of ceramic 30 hollow spheres, diatomite, wollastonite, ground rice hulls, perlite, vermiculite, expanded polystyrene, gypsum, calcium carbonate, alumina hydrate, and silica flour, and wherein the additives maybe further selected from the group - 19 consisting of organic additives ofplasticising agents and biopolymers.

20. A dewatering aid for dewatering a cementitious slurry coating on a product substantially as herein described with reference to any one of the 5 embodiments of the invention illustrated in the accompanying figures and examples but excluding comparative examples.