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Get to know gypsum the building material

The diverse material

Gypsum is an essential part of our natural habitat: Karst landscapes are impressive with their widely varied vegetation and numerous morphological manifestations. And man has always used and left his mark on this "gypsum habitat". Gypsum rock is one of the most important mineral building materials. Not necessarily the quantity, even though 4 – 5 million tonnes is no longer a small quantity. More important is its significance, particularly for drywalling construction in interiors.



Nature is inventive

The inventive spirit of nature is ingenious. Gypsum, a rock that is more than 200 million years old, is so easy to use that it has been employed as a building material for millennia. In ancient Jericho, walls and floors were made of gypsum more than 11,000 years ago. This material enjoyed a true renaissance in the master craftsmanship employed in baroque stucco work. Today, gypsum is used to ensure a comfortable living environment and for creative room design.

Securing the raw material base

It is hardly surprising that the demand is increasing steadily for this "miraculous material". In the close interrelation between the most modern energy technology and intelligent processes, Knauf ensures that gypsum will also be available in the future as an environmentally-friendly material.

Natural gypsum

The white natural gypsum stone was formed over several geological eras.

Gypsum was formed between 100 and 200 million years ago. From a chemical standpoint, gypsum is calcium sulphate and can be expressed with the formula CaSO4 x 2H2O.

It was formed by sedimentation during evaporation of seawater in the flat basins distributed across the surface of the earth. During the course of geological history, as the gypsum deposits were covered by other rock material or subject to other geological influences, they lost their crystallized water, and anhydrite (CaSO4) was formed. As soon as waterless anhydrite comes into contact with water, it gradually reverts back into gypsum.

Both natural materials are important in the manufacture of our products. They are mined in both open-cast and underground mines.

FGD gypsum

Flue gas desulphurization plant gypsum (FGD) as a raw material for the building materials industry.

The German Federal Emission Control Law (Bundesimmissionsschutzgesetz) from 1983, stipulates that fossil fuel based combustion plants require flue gas desulphurization plants (FGD). Thus, a very significant step for air purity was taken in Germany.

We at Knauf made a significant contribution in developing the desulphurization technology. It is a simple, wet cleaning procedure utilizing natural limestone resulting in an end product of moist, fine desulphurized flue gas gypsum that is delivered directly as a raw material to the economic cycle of the building materials industry.

Both the technology for desulphurization as well as the development for the application of FGD gypsum in the building materials industry is based on our research and development work and our comprehensive know-how as well as close cooperation with the operators of power plants. This process has prevailed in both Western and Eastern Europe. A good example of European cooperation and an important contribution to global conservation of nature and the environment.

FGD gypsum is created using the same principles as natural gypsum. Now this process at an accelerated pace takes just a few hours, whereas nature requires millions of years for the formation of natural gypsum deposits.

Alpha hemihydrate

Alpha hemihydrate is a fascinating raw material with exceptional properties. Our manufacturing sites in Germany allow us to manufacture promptly and flexibly – with premium quality.

Alpha hemihydrate as a raw material is a very reactive and highly stable binder that will react with water within a very short period without a catalyst. It is synthesized by subjecting FGD gypsum to pressurized steam treatment at a maximum temperature of 150 °C.

The compact crystal with a low specific surface and low water demands produces hard, low porosity casts. Alpha hemihydrate is used primarily in industrial mixtures based on its high strength and quick setting features, such as in the manufacture of moulding gypsums, gypsum based building materials and special gypsums for areas of application with specialized requirements.

Thermal anhydrite

The thermal anhydrite raw material is obtained by calcinating FGD gypsum at a temperature of at least 700 °C.

The process completely expels the water of crystallisation from the FGD gypsum and the surface of the anhydrite (CaSO4) that is formed is reduced by sintering to ensure a more favourable mixing water requirement. As a moist, particulate flue gas gypsum (also called FGD gypsum), the thermal anhydrite is directed straight into the economic cycle of the building material industry, and its uniform grain size makes it the exemplary manufacturing solution for many products.


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