WATER-RESISTANT BUILDING MATERIAL

Abstract: The present invention relates to a water-resistant building material which comprises: 0.2 to 6 % by weight of water-proofing additive; 0.5 to 10 % by weight of fly ash; 0 to 5 % by weight of Portland cement; and the balance being gypsum and optionally at least one other additive, all of the above percentages by weight being based on the weight of the total composition. The present invention also provides a method for producing the water-resistant building material and a water-resistant plasterboard construction containing the water-resistant building material.

Description: WATER-RESISTANT BUILDING MATERIAL The present invention relates to a water-resistant building material, such as, a panel or sheet. The building materials currently used in internal wet areas, such as, behind tiles in shower recesses or for external protected areas, for example, eaves lining, are composed of compressed cellulose cement or water-resistant plasterboard. A requirement accordingly exists for a water-resistant building material which has improved long term water-resistance and maintains an acceptable strength after considerable exposure to moisture. According to the present invention there is provided a water-resistant building material which comprises: 0.2 to 6% by weight of water-proofing additive; 0.5 to 10% by weight of fly ash; 0 to 5% by weight of Portland cement; and the balance being gypsum and optionally at least one other additive, all of the above percentages by weight being based on the weight of the total composition. Further according to the present invention there is provided a method for producing a water-resistant building material which comprises: mixing 0.2 to 6% by weight of water-proofing additive, 0.5 to 10% by weight of fly ash, 0 to 5% by weight of Portland cement and the balance being plaster of Paris and optionally at least one other additive with water to form a slurry; pouring the slurry into a mould; allowing the slurry to hydrate and set; and drying the building material at 50 to 150 °C. Still further according to the present invention there is provided a water-resistant plasterboard construction which comprises: at least one layer of fabric; and a layer of the water-resistant building material described above. The water-resistant building material is preferably a sheet or panel for internal or external use. The water-proofing additive may be of any suitable known type, for example, melamine formaldehyde, polyvinyl alcohol, paraffin wax emulsion, silicone emulsion, silicone oil, polyvinyl acetate and bitumen emulsion. Preferably, the concentration of water-proofing additive in the building material is 0.4 to 4% by weight of the total composition. The concentration of fly ash in the building material is preferably 1 to 6% by weight of the total composition. Preferably, the concentration of Portland cement in the building material is 0 to 3% by weight of the total composition. The concentration of gypsum in the building material is preferably 80 to 96% by weight of the total composition. The other additive which may be present includes fibrous reinforcement, for example, cellulose fibre or chopped fibreglass and light weight filler, for example, waterproof perlite. It will be appreciated that the present invention is not limited to these additives and may include other additives used in the art. The improved water-resistance is preferably obtained by incorporating low concentrations of fly ash and optionally Portland cement with the plaster of Paris, together with the water-proofing additive. The water-proofing additive acts in conjunction with the low concentrations of ettringite formed and this significantly improves the long term water-resistance compared with that achieved by using the water-proofing additive or the fly ash and Portland cement. Thus, in a particularly preferred embodiment, the water-resistant building material comprises: 80 to 96% by weight of gypsum; 0.2 to 6% by weight of water-proofing additive; 0.5 to 10% by weight of fly ash; 0 to 5% by weight of Portland cement; 0.2 to 3% by weight of fibrous reinforcement; and 0 to 2% by weight of light weight filler, all of the above percentages by weight being based on the weight of total composition. The water-resistant plasterboard construction preferably comprises one layer of fabric and one layer of paper with the water-resistant building material being sandwiched therebetween. The fabric preferably forms the layer which is exposed to the water. The fabric may be composed of either naturally occurring fibres or man-made fibres. Preferably, the fabric is composed of man-made fibres based on natural organic polymers such as rayon or of man-made fibres based on synthetic organic polymers such as olefin. Particularly preferred fabrics are viscose rayon, more preferably Lantor (Registered Trade Mark) filter or spunbonded polypropylene, more preferably Evolution (Registered Trade Mark) fabric. The water-resistant plasterboard construction may be produced by any suitable known process, preferably a continuous process. A particularly preferred continuous process will now be described by way of example only with reference to the accompanying drawing in which: Figure 1 is a side view of a continuous process for the production of a water-resistant plasterboard construction in accordance with the invention. As shown in the accompanying drawing, the components of the water- resistant building material 2 are metered into a mixer 4 which discharges a slurry 6 onto a layer of paper 8 which is transferred onto a conveyer belt 10. The fabric layer 12 then sandwiches the slurry and after the edges are sealed, the water-resistant building material 2 is allowed to set. During setting, the slurry impregnates the fabric and on setting the gypsum crystals formed provide a strong bond with the fabric. The fabric reinforces the surface and contributes significantly to the flexural strength of the plasterboard construction. After the water-resistant building material has set, the plasterboard is cut into desired lengths and dried. The invention is further described in and illustrated by the following Examples. The Examples are not to be construed as limiting the invention in any way. The percentages quoted in the Examples are by weight of the total composition. Example 1 Plaster of Paris 80-96% Water-proofing additive 0.2-6% Fly ash 0.5-10% Portland cement 0-5% Fibrous reinforcement 0.2-3% Waterproof perlite 0-2% The above components were mixed with water in a ratio of 50-90mls of water to lOOgms of powder and other liquid additives used in the art to form a slurry. The slurry was mixed using a suitable mixer such as a propeller type mixer, and was poured into a mould and allowed to hydrate and set. After setting the mould was removed and the cast building slab was dried in a heated air circulating drying kiln. TTie water resistant building materials described in the following Examples 2 to 9 were produced in the same manner as Example 1. 6 - Example 2 Plaster of Paris 80-96% Silicone 10% Fly ash 0.5-10% Portland cement 0-5% Waterproof perlite 0-2% Drying temperature 90 °C 10 day water absorption 8.2% Flexural strength 200 Newtons Example 3 Plaster of Paris 80-96% Silicone 4% Fly ash 2% Portland cement 0-5% Fibrous reinforcement 0.2-3% Waterproof perlite 0-2% Drying temperature 70 °C 10 day water absorption 6.9% Flexural Strength 240 Newtons Example 4 Plaster of Paris 80-96% Silicone 1% Fly ash 2% Portland cement 0-5% Fibrous reinforcement 0.2-3% Waterproof perlite 0-2% Drying temperature 50 °C 10 day water absorption 5.0% Flexural Strength 250 Newtons Example 5 Plaster of Paris 80-96% Silicone 1% Fly ash 2% Portland cement 0-5% Fibrous reinforcement 0.2-3% Waterproof perlite 2% Drying temperature 50 °C 10 day water absorption 2.9% Example 6 Plaster of Paris 80-96% Silicone 1% Fly ash 2% Portland Cement 0.5% Fibrous reinforcement 0.2-3% Waterproof perlite 0-2% Drying temperature 80 β C 10 day water absorption 6.0% Example 7 Plaster of Paris 80-96% Paraffin wax emulsion 8% Fly ash 5% Portland cement 0-5% Fibrous reinforcement 0.2-3% Waterproof perlite 0-2% Drying temperature 90 °C 10 day water absorption 6.5% Example δ Plaster of Paris 80-96% Paraffin wax emulsion 10% Fly ash 3% Portland cement 0-5% Fibrous reinforcement 0.2-3% Waterproof perlite 0-2% Drying temperature 60 °C 10 day water absorption 5.5% Example 9 Plaster of Paris 80-96% Paraffin wax emulsion 6% Fly ash 1% Portland cement 1% Fibrous reinforcement 0.2-3% Waterproof perlite 0-2% Drying temperature 80 °C 10 day water absorption 4.3%

Claims: CLAIMS 1. A water-resistant building material which comprises: 0.2 to 6% by weight of water-proofing additive; 0.5 to 10% by weight of fly ash; 0 to 5% by weight of Portland cement; and the balance being gypsum and optionally at least one other additive, all of the above percentages by weight being based on the weight of the total composition. 2. A water-resistant building material as claimed in Claim 1 wherein the water-proofing additive is selected from melamine formaldehyde, polyvinyl alcohol, paraffin wax emulsion, silicone emulsion, silicone oil, polyvinyl acetate and bitumen emulsion. 3. A water-resistant building material as claimed in Claim 1 or Claim 2 wherein the concentration of water-proofing additive is 0.4 to 4% by weight of the total composition. 4. A water-resistant building material as claimed in any one of the preceding claims wherein the concentration of fly ash is 1 to 6% by weight of the total composition. 5. A water-resistant building material as claimed in any one of the preceding claims wherein the concentration of Portland cement is 0 to 3% by weight of the total composition. 6. A water-resistant building material as claimed in any one of the preceding claims wherein the concentration of gypsum is 80 to 96% by weight of the total composition. 7. A water-resistant building material as claimed in any one of the preceding claims wherein the at least one other additive is fibrous reinforcement and/or light weight filler. 8. A water-resistant building material as claimed in Claim 7 wherein the fibrous reinforcement is cellulose fibre or chopped fibregiass. 9. A water-resistant building material as claimed in Claim 7 or Claim 8 wherein the light weight filler is waterproof perlite. 10. A water-resistant building material as claimed in any one of the preceding claims which comprises: 80 to 96% by weight of gypsum; 0.2 to 6% by weight of water-proofing additive; 0.5 to 10% by weight of fly ash; 0 to 5% by weight of Portland cement; 0.2 to 3% by weight of fibrous reinforcement; and all of the above percentages by weight being based on the weight of total composition. 11. A water-resistant building material as claimed in any one of the preceding claims which is in the form of a sheet or panel for internal or external use. 12. A method for producing a water-resistant building material as claimed in any one of the preceding claims which comprises: mixing 0.2 to 6% by weight of water-proofing additive, 0.5 to 10% by weight of fly ash, 0 to 5% by weight of Portland cement and the balance being plaster of Paris and optionally at least one other additive with water to form a slurry; pouring the slurry into a mould; allowing the slurry to hydrate and set; and drying the building material at 50 to 150 °C. 13. A water-resistant plasterboard construction which comprises: at least one layer of fabric; and a layer of the water-resistant building material as claimed in any one of Claims 1 to 11. 14. A water-resistant plasterboard construction as claimed in Claim 13 wherein the fabric is composed of either naturally occurring fibres or man- made fibres. 15. A water-resistant plasterboard construction as claimed in Claim 13 or Claim 14 wherein the fabric is composed of man-made fibres based on natural organic polymers or of man-made fibres based on synthetic organic polymers. 16. A water-resistant plasterboard construction as claimed in Claim 15 wherein the man-made fibres based on natural organic polymers is rayon. 17. A water-resistant plasterboard construction as claimed in Claim 15 wherein the man-made fibres based on synthetic organic polymers is olefin. 18. A water-resistant plasterboard construction as claimed in any one of Claims 13 to 15 wherein the fabric is viscose rayon or spunbonded polypropylene. 19. A water-resistant plasterboard construction as claimed in Claim 18 wherein the viscose rayon is Lantor (Registered Trade Mark) filter. 20. A water-resistant plasterboard construction as claimed in Claim 18 wherein the spunbonded polypropylene is Evolution (Registered Trade Mark) fabric. 21. A water-resistant plasterboard construction as claimed in any one of Claims 13 to 20 which comprises one layer of fabric and one layer of paper with the water-resistant building material being sandwiched therebetween. 22. A water-resistant plasterboard construction as claimed in any one of Claims 13 to 21 wherein the fabric forms the layer which is exposed to the water.

Inventors: BROWN GRAEME ALEXANDER, KOJIC DRAGAN, RICHARDS COLIN DAVID, BROWN, GRAEME, ALEXANDER, KOJIC, DRAGAN, RICHARDS, COLIN, DAVID
Applicants: AUSTRALIAN GYPSUM, BORAL AUSTRALIAN GYPSUM LIMITED
Application year: 1992
Main classification: B32B13
IPC codes: B32B13, C04B28