For centuries, walls and ceilings have been coated with a layer of finishing plaster to cover the construction prior to painting them. Plaster was a paste of powdered gypsum, lime or cement mixed with water and applied to the walls. Mixing water with the powder triggered an exothermic process, causing solidification of the paste. During the 1950s, drywall or plasterboard replaced the traditional plastering methods. Drywall also called Sheetrock is a core of gypsum sandwiched between paper liners or fiber glass mats, to form ready-made panels that can be installed to the building interiors. Gypsum board, plasterboard, and wallboard are the other terminologies referring to drywall.
Manufacture
The drywall manufacturing process is phased into 5 stages – stucco preparation, mixing, forming, drying and finishing. Gypsum is partially dehydrated in a calcining process in flash calciners. The powder is mixed with paper pulp or fiber and other additives that give the specific variety of drywall the desired degree of qualities – like fire resistance, moisture resistance, sound proofing, etc. Water is added to the mixture and the slurry is treated with a surfactant to permit air entrainment that gives the ability to cut, fit and nail the boards. The slurry is then poured over a long roll of paper on a conveyor belt, and wrapped by another roll of paper. The sandwiched mixture is compacted and formed to desired thickness and edges. The mixture is set, cut to panel sizes and dried in ovens.
Types and installation
Drywall can be generally classified into fire-resistant, water-resistant and other types. The panels are commonly available in 48-inch and 54-inch wide sizes, ½ inch and 5/8 inch thickness and varying lengths. The installation process is quite easy, the main challenge being the ceiling. Once the crucial part is complete, the entire process should complete within a day or 2. The panels are cut to desired sizes and fastened to walls and ceilings using drywall screws, and the seams are secured using joint tapes.
Material composition
The primary materials that compose the boards are gypsum and paper. Gypsum is available in plenty all over the world, and is also obtained as a by-product from flue gas desulfurization. The by-product is called synthetic gypsum, and is combined with virgin gypsum in varying percentages in the making of drywall. Paper that is used is almost always recycled newspaper. Renewable materials like agricultural corn and starch are used as binders, and the additives, which form a minimal percentage of the composition, are chosen based on the board type.
Drywall is considered as a passive fire protection material, as it is an ablative and vaporizes when set on fire, preventing spread of flame.
Volatile organic compounds (VOCs) are organic chemicals available in paints and coatings that have been identified to cause a lot of harm to the environment and human health. Reduction of VOC emissions in materials used for interiors is one of the primary focus areas in constructing green buildings. The gypsum boards are considered as low emitters of VOCs. Presently, most of the raw materials used in the making of drywall are entirely recycled stuff. Gypsum by itself is non-toxic and is considered beneficial to environment. Continuous improvements have been made to reduce energy consumption and carbon dioxide emission in the manufacturing process.
Owing to its inherent qualities and the Eco-friendly manufacturing processes employed, the gypsum board has been branded as an Eco-friendly building material.
Recycling drywall
Drywall wastes increase with frequent rebuilding, and remodeling. Earlier drywall waste was just discarded into landfills. Improper disposal caused more environmental damage and the new challenge faced by authorities and environment activists is to recycle discarded drywall. A lot of study and research has gone into its treatment and disposal. Pulverizing discarded drywall gives about 90% gypsum, shredded paper and a certain amount of acceptable waste. The gypsum is simply used for soil treatment or as raw material for new drywall.
Issues
During the start of the century, the construction industry in USA faced a steep rise in requirement of drywalls, and had them imported in large quantities from China. Residences in certain parts of America saw a rise in sulfur emissions causing a lot of health issues. Complaints of copper corrosion and bad odor were later traced to pyrite oxidation in specific climes, causing release of sulfur compounds and deterioration in indoor air quality.
The lesser serious issues are – broken old water pipelines causing mold and mildew on drywall, creation of provisions for fire-stop, drywall sag in ceilings, etc. Choosing the right variation or type and making of drywall based on location, climate, building type and thinking through the plan carefully before installing. The interiors would go a long way in creating an Eco-friendly and pleasant surrounding.
