Lightweight construction panels, such as gypsum plaster-board, are commonly used to provide internal partitions in buildings It is known to cover, either partially or fully, the panel with an aqueous material such as gypsum plaster or jointing compound. It has been found that known panels expand when they absorb water. This gives rise to several undesirable results such as the gypsum plaster or jointing compound cracking as the panel expands as moisture is absorbed. The present invention provides a panel comprising a gypsum matrix including fibres in an amount of at least 0.8 wt % relative to the gypsum, a polymeric additive in an amount of at least 0.8 wt % relative to the gypsum, and at least one phosphate additive. A panel having such a composition has been found to have desirable characteristics.

A fire-resistant gypsum panel comprises: a gypsum core layer comprising set gypsum and a high temperature sag-resistant material including mineral wool in an amount between 0.2% and 3.0% by weight of gypsum.

This invention provides low dust low density gypsum wallboard products having high total core void volumes, corresponding to low densities in the range of about 10 to 30 pcf. The wallboards have a set gypsum core formed between two substantially parallel cover sheets, the set gypsum core preferably having a total void volume from about 80% to about 92%, and made from a slurry including stucco, pregelatinized starch, and a naphthalenesulfonate dispersant. The combination of the pregelatinized starch and the naphthalenesulfonate dispersant also provides a glue-like effect in binding the set gypsum crystals together. The wallboard formulation, along with small air bubble voids (and water voids) provides dust control during cutting, sawing, routing, snapping, nailing or screwing down, or drilling of the gypsum-containing products. This invention also provides a method of making the low dust low density gypsum products including the introduction of soap foam in an amount sufficient to form a total void volume, including air voids, preferably from about 80% to about 92% in the set gypsum core, corresponding to a set gypsum core density from about 10 pcf to about 30 pcf. The wallboards produced by the method generate significantly less dust during working.

Systems and methods for making gypsum board using a liquid gypsum set accelerator. Stucco and water are mixed to form a gypsum slurry, such as in a pin mixer. A gypsum set accelerator is mixed with a liquid medium to form a liquid gypsum set accelerator, such as in an eductor. The liquid gypsum set accelerator is added to the gypsum slurry, which is shaped to form the gypsum board.

A liquid accelerator composition for accelerating the setting reaction of calcium sulfate hemihydrate and water and methods of forming a liquid gypsum accelerator are provided. The liquid accelerator composition includes a liquid media in which calcium sulfate dihydrate is less than fully soluble and a ground product of a mill grinding of a mixture comprising calcium sulfate dihydrate.

The invention concerns a method for producing gypsum boards, wherein a liquefier for the gypsum slurry is foamed with gas to provide a foam having a water content of less than 85 wt.-%, then incorporated into a gypsum/water mixture and the mixture thus obtained is applied on a two dimensional substrate. The incorporation of the liquefier in foamed form allows for a significant reduction of the amount of liquefier required to provide a desired flowability of the gypsum/water mixture, thus allowing the production of gypsum boards with similar characteristics with less liquefier. The invention further concerns gypsum board prepared using this process, apparatuses for producing gypsum boards using this process and the use of a corresponding liquefier foam to minimize the amount of liquefier required to establish a desired flowability of a gypsum/water mixture.

Disclosed is a composite gypsum board comprising a set gypsum core disposed between face (e.g., Manila) and back (e.g., Newsline) cover sheets. The set gypsum core is formed from a core slurry comprising stucco, water, and optional additives, such as foaming agent, migrating starch, accelerator, retarder, dispersant, etc. A dense layer formed from a dense layer slurry comprising stucco, water, fiber (e.g., paper fiber), and optionally, strength-enhancing starch, is disposed between the core and the face paper. The dense layer slurry contains a greater concentration of fiber, and optionally, strength-enhancing starch, than the core slurry, but the concentration of one or more other additives (e.g., accelerator, retarder, dispersant, or combinations thereof) is lower or the same in the dense slurry as compared with the core slurry. Also disclosed is a method of making board using one board mixer. In embodiments, paper fiber is added to water to form a suspension. The suspension is introduced, while in a non-laminar state, into the dense slurry. Further disclosed is apparatus, such as an extractor and an additive injection system, which can be a part of a cementitious slurry mixing and dispensing assembly.

Method for producing a cementitious board (1), wherein a first liner (2) with first overlap sections (5) is provided and furnished with at least one layer of at least one slurry comprising a cementitious material (3); a second liner (4) with second overlap sections (8) is provided and arranged such that it contacts the first overlap sections (5) of the first liner (2), wherein the at least one layer of the at least one slurry (3) is arranged between the first liner (2) and the second liner (4); an adhesive foam (6) is provided at least partly on at least one of the first or second overlap sections (5, 8); and the first liner (2) and the second liner (4) are bonded via the adhesive foam (6) in the overlap sections (5, 8).

Disclosed are an organic binder-based coating; a composite gypsum board containing face and back cover sheets, an outside surface of the back cover sheet bearing the coating; and a method of preparing composite board where the back cover sheet contains the coating on its outer surface. The coating is formed from a composition comprising an alkaline silicate, a solid filler, and optionally, a borate. An enhancing layer can also be applied to the back cover sheet.

Gypsum board having improved performance is obtained by controlling the distribution of starch in the gypsum core of the board and the gelling temperature of the starch. Starch migration in the board is controlled by the degree of acid-modification, to adjust the starch viscosity profile. The starch gelling temperature is controlled by chemical modification of the starch —OH groups.