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Gypsum is monoclinic, high degree of cleavage, easy to crack into thin slices. Gypsum will be heated to 100 ~ 200 ° C, the loss of part of the crystal water, semi-water gypsum can be obtained. It is a gas-hardening cementitious material, with α and β two forms, are diamond-shaped crystals, but the physical properties of different. Β-type hemihydrate gypsum is flaky and cracked crystals, the crystal is very fine, the specific surface area is much larger than the α-type hemihydrate gypsum.

Production of gypsum products, α-hemihydrate gypsum less than β-type water requirements, products have a higher density and strength. Usually steam autoclave autoclave in saturated steam is made of α-hemihydrate gypsum, also known as high-strength gypsum; frying pan or rotary kiln open device calcined from the β-type hemihydrate gypsum, which is building plaster. Industrial by-products Chemical gypsum has the same properties as natural gypsum and does not require excessive processing. Half-water gypsum and water mixing slurry to re-form dihydrate gypsum, in the drying process of rapid coagulation and hardening to obtain strength, but the water is softened.

Gypsum is the production of gypsum cementitious materials and gypsum building products, the main raw material, but also Portland cement retarder. Calcined gypsum calcined at 600 ~ 800 ° C, adding a small amount of lime and other catalysts together fine, can be obtained anhydrite cementing material (also known as the cementing material); by 900 ~ 1000 ° C calcination and grinding, can be calcined high-temperature gypsum . Products made with these two kinds of gypsum, the strength is higher than the building gypsum products, and anhydrite cementing material has good insulation, high-temperature calcined gypsum has good wear resistance and water resistance.

The use of building gypsum production of building products are:

① paper gypsum board. In the building gypsum by adding a small amount of adhesive, fiber, foam and other water mixed with continuous casting in the two layers between the protective paper, and then by rolling, solidification, cutting and drying. Thickness 9 ~ 25 mm, dry bulk density 750 ~ 850 kg / m 3, sheet toughness, non-flammable, dimensional stability, surface smooth, can be cut, easy to construct. Mainly used for interior walls, interior wall veneer, ceilings, acoustic panels, but poor water resistance, should not be used for wet environments.

② fiber gypsum board. Will be mixed with fiber and other admixtures of building gypsum slurry, with winding, pressing or roll forming method, after cutting, solidification, drying. Thickness is generally 8 to 12 mm, compared with the paper gypsum board, the bending strength is higher, do not protect the surface of paper and adhesive, but the bulk density is larger, use the same with the plaster board.

③ decorative gypsum board. Will be prepared by the construction of gypsum slurry, pouring in the bottom mold with a pattern of the box, the smoothing, solidification, stripping, drying, thickness of 10 mm. In order to improve its sound absorption effect, can also be made with perforated and blind holes of the plate, commonly used for ceiling and decorative wall.

④ gypsum hollow slab and gypsum block. Casting gypsum slurry into the mold, the vibration molding and solidification after stripping, drying. Hollow slab thickness is generally 60 to 100 mm, hole rate of 30 to 40%; block size is generally 600 × 600 mm, thickness 60 ~ 100 mm, around the mouth of the mouth, and sometimes can be made with a hollow hole Block. Hollow slabs and blocks are dedicated gypsum masonry, construction is convenient, commonly used for non-load-bearing wall.