Plasterboard manufacture

In a method of making gypsum plasterboard by the steps of forming an aqueous slurry of calcium sulphate plaster, including starch as a dry bond assistant therefor, encasing the slurry between paper sheets, allowing said slurry to set to form a core and drying said board, the improvement which comprises applying to at least those faces of the paper sheets that contact the slurry, a solution consisting of a water-soluble zirconium salt and a solvent therefor, and contacting said sheets with said slurry during manufacture of the board, the use of said zirconium salt enabling a reduction to be made in the amount of starch required in the plaster slurry to produce an adequate dry bond.

In a method of making plaster or gypsum board by the steps of forming an aqueous slurry of calcium sulphate plaster, including starch as a dry bond assistant therefor, encasing the slurry between paper sheets, allowing said slurry to set to form a core and drying said board, the improvement which comprises applying to at least those faces of the paper sheets that contact the slurry, a solution consisting of a water-soluble zirconium salt and a solvent therefor, and contacting said sheets with said slurry during manufacture of the board, thereby causing said zirconium to inhibit migration of said starch whereby a dry bond between said sheets and said core can be achieved at a reduced level of starch in said slurry.

In a method of making gypsum plasterboard by the steps of forming an aqueous slurry of calcium sulphate plaster, including starch as a dry bond assistant therefor, encasing the slurry between paper sheets, allowing said slurry to set to form a core and drying said board, the improvement which comprises applying to at least those faces of the paper sheets that contact the slurry, a solution consisting of a water-soluble zirconium salt and a solvent therefor, and substantially immediately thereafter contacting said sheets while still wet from said solution with said slurry to manufacture said board, the use of said zirconium salt enabling a reduction to be made in the amount of starch required in the plaster slurry to produce an adequate dry bond.

In a method of making gypsum plasterboard by the steps of forming an aqueous slurry of calcium sulphate plaster, including starch as a dry bond assistant therefor, encasing the slurry between paper sheets, allowing said slurry to set to form a core and drying said board, the improvement which comprises using as said sheets, paper wherein the face that contacts said slurry is soft sized or substantially unsized, applying to at least those faces of the paper sheets that contact the slurry a solution consisting of a water soluble zirconium salt and a solvent therefor and contacting said sheets with said slurry during manufacture of the board, the use of said zirconium salt enabling a reduction to be made in the amount of starch required in the plaster slurry to produce an adequate dry bond.

In a method of making plaster or gypsum board by the steps of forming an aqueous slurry of calcium sulphate plaster, including starch as a dry bond assistant therefor, encasing the slurry between paper sheets, allowing said slurry to set to form a core and drying said board, the improvement which comprises using as said sheets, paper wherein the face that contacts said slurry is soft sized or substantially unsized , applying to at least said face of said sheets a solution consisting of a water-soluble zirconium salt and a solvent therefor and substantially immediately thereafter contacting said sheets while still wet from said solution with said slurry to manufacture said board, thereby causing said zirconium to inhibit the migration of said starch whereby a dry bond between said sheets and said core can be achieved at a reduced level of starch in said slurry.