assembly can withstand a standardized fire test. Often perlite, vermiculite, and boric acid are added to improve fire resistance. Greenboard, the drywall containing an oil-based additive in the green-colored paper covering, provides moisture resistance. It is commonly used in washrooms and other areas expected to experience elevated humidity levels. Blueboard, blue face paper forms a strong bond with a skim coat or a built-up plaster finish, providing water and mold resistance. Cement board, which is more water-resistant than greenboard, for use in showers or sauna rooms, and as a base for ceramic tile. Soundboard is made from wood fibers to increase the sound transmission class. Soundproof drywall is a laminated drywall made with gypsum and other materials such as damping polymers to significantly increase the sound transmission class rating. Mold-resistant, paperless drywall with fiberglass face Enviroboard, a board made from recycled agricultural materials Lead-lined drywall, a drywall used around radiological equipment. Foil-backed drywall used as a vapor barrier. Controlled density (CD), also called ceiling board, which is available only in thickness and is significantly stiffer than the regular whiteboard. EcoRock, a drywall that uses a combination of 20 materials including recycled fly ash, slag, kiln dust and fillers and no starch cellulose; it is advertised as being environmentally friendly due to the use of recycled materials and an energy efficient process. Gypsum "Firecode C". This board is similar in composition to Type X, except for more glass fibres and a form of the vermiculite used to reduce shrinkage. When exposed to high heat, the gypsum core shrinks, but this additive expands at about the same rate, so the gypsum core is more stable in a fire and remains in place even after the gypsum dries up. Waste Because up to 12% of drywall is wasted during the manufacturing and installation processes and the drywall material is frequently not reused, disposal can become a problem. Some landfill sites have banned the dumping of drywall. Some manufacturers take back waste wallboard from construction sites and recycle them into new wallboard. Recycled paper is typically used during manufacturing. More recently, recycling at the construction site itself has been researched. There is potential for using crushed drywall to amend certain soils at building sites, such as sodic clay and silt mixtures (bay mud), as well as using it in compost. As of 2016, industry standards are being developed to ensure that when and if