Pure gypsum is a white rock but sometimes impurities colour it grey, brown or pink. Its scientific name is calcium sulphate dihydrate and its chemical formula is CaSO42H2O. This means that, for every molecule of gypsum, there are two molecules of water. If a piece of gypsum is ground to powder and heated, it will lose about three quarters of its water. If this powder is then mixed with water, the paste or slurry will set rock hard. The chemically-combined water, previously removed, has re-combined and the material has reverted to the original composition of the rock.

The powder is called hemi-hydrate gypsum plaster (Plaster of Paris). Gypsum plaster has been used in buildings for literally thousands of years.

Gypsum is found in every continent of the world. We have mentioned France, but gypsum is also mined and quarried throughout Europe. India and Pakistan have gypsum and so have Africa, Australia, China, Japan and South America. There are gypsum mines across North America, and Utah possesses large deserts of powdery gypsum rock. Gypsum is also obtained as a by-product of reducing the emissions levels of coal-fired power stations.

In 1890 the works of the New York Coal Tar Chemical Company, Augustine Sackett and Fred L. Kane used manilla paper and plaster of Paris to create a stiff, strong, new material - plasterboard. By 1909, Augustine Sackett was producing nearly 47 million square metres of plasterboard a year. In 1917 plasterboard came to Britain. The first factory in Europe was set up in Wallasey, Cheshire. It is a success story that continues to this day and plasterboard is recognised for its properties of acoustic insulation, fire resistance, thermal insulation and usefulness in modern methods of construction.

Gypsum is a non-hazardous mineral.

Why does gypsum waste have to be disposed of in a separate landfill?

From 1st April 2009 the guidance on landfill changed. Visible gypsum waste can no longer be disposed to general landfill, but must go to a separate cell for non-hazardous high-sulphate material. This is because gypsum mixed with waste organic material can give off hydrogen sulphide gas (bad eggs smell).

What is By-product Gypsum?

By-product gypsum is produced as a waste from other industrial processes. In this country this is primarily produced from the cleaning process at coal powered power-stations. Over 60% of all the gypsum used for making plaster and plasterboard products in the UK now comes from recycled by-product gypsum reducing the demand for natural gypsum and preserving the long term stocks of the mineral.

For waste sites accepting plasterboard, please click on the following link:-

http://www.netregs.gov.uk/netregs/98247.aspx