Plasterboard is one of the great versatile materials in modern construction. Made from the simple materials of gypsum and paper it is used in most building types in a wide range of applications including wall lining, partitions, sound control and fire protection
The main environmental impacts associated with plasterboard result from the production process, transportation and disposal. Efforts directed by government currently concentrate on reducing the quantity of plasterboard being diverted from landfill to be recycled.
Around 270 million m2 of plasterboard is manufactured annually using some 3 million tonnes of gypsum. Representing around 60% of the total annual output, gypsum used in plasterboard is generated by from natural and synthetic sources:
Naturally occurring gyspum
Gypsum (CaSO4.2H2O) is the hydrated form of Calcium Sulphate (CaSO4). Calcium Sulphate is a by-product of the evaporation of lake and seawater and occurs in beds up to several metres thick. Calcium Sulphate Dihydrate (Gypsum) is commonly hydrated by groundwater.
The UK is largely self-sufficient in gypsum. The material can be found in seams in the Pennines and the Midlands, but the biggest source of extraction is in East Sussex where mining extracts some 100,000 tonnes of gypsum a year from 100 m below the High Weald. The mined rock is reduced to powder through a process of crushing and grinding.
Synthetic or Glue Gas Desulphurisation (FGD) gypsum
This gypsum is a by-product of the desulphurisation of the flue gases of coal-fired powerstations. Sulphur dioxide emission control systems remove sulphur from combustion gases using 'scrubbers.' One particular type of scrubber that uses lime or limestone reagent system produces 'FGD gypsum' which is chemically nearly identical to mined natural gypsum.
Though currently contributing towards a significant proportion of overall gypsum production in the UK, this is likely to have peaked as the country moves towards reducing dependence on coal-fired power stations (assuming no substantial breakthrough in carbon capture and storage technology / change in energy policy).
Plasterboard production
'Stucco' is produced by removing around 75% of the water from the gypsum through heating using natural gas to a temperature of over 150'C. This process of 'calcination' changes calcium sulphate from its dihydrate state (gypsum) to its hemihydrate state.
The hemihydrate calcium sulphate (CaSO4.½H2O) is now ready to form plasterboard.
Water, as well as other additives to control production and performance, is added to the stucco. The slurry is poured onto a moving belt of facing paper where a further paper is applied as a top cover and spreads the slurry to set the width and thickness of the plasterboard.
The resulting wet sandwich of paper and plaster is cut to board lengths as the plaster sets quickly before being transferred to a drying line which carries the boards through a gas-heated kiln. When the slurry has dried and hardened it has effectively reverted back to being gypsum rock.
Once dry, the boards are trimmed and stacked ready for despatch and use.
Common additives
• Starch - protects the physical bond between gypsum crystals and facing paper during drying.
• Lignosulphates - Improves the flow of the slurry so less water is required, resulting in denser plaster.
• Potassium sulphate - Causes the gypsum to precipitate out more quickly due to a common ion effect.
• Foaming agent (detergent) - Forms a foam in the mix, resulting in a less denser plaster.
• Silicone - plasterboard is inherently vulnerable to moisture, silicone is added for use in damp conditions
• Wax - also added to provide resistance to moisture
• Vermiculite - added to specifically designated fire resistant boarding
• Glass fibre - also added to provide increased fire protection.