What is Gypsum?
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.
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.