Drywall

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Background

Drywall is a construction material made up of thin panels of gypsum board. It consists of gypsum rock layered between two sheets of specialized paper. This form of construction is much more efficient compared to the older method of applying wet plaster to gypsum laths.

Besides its ease of installation, drywall also offers some fire resistance to buildings. Gypsum contains a significant amount of water in crystalline form; for instance, 10 square feet of gypsum board holds over 2 quarts of water. When exposed to fire, the water within the gypsum evaporates, keeping the panel's temperature at 212°F (100°C) until all water is released, thereby protecting the wood beneath. Even after the water is gone, gypsum itself doesn't burn and continues to offer fire protection.

Gypsum plaster has been a construction material for thousands of years. Remarkably, plaster dating back at least 4,000 years still survives in excellent condition inside Egypt's Great Pyramids. Today, drywall is essential in modern construction globally.

Raw Materials

The key ingredient in drywall is the mineral gypsum, a lightweight rock found abundantly around the world. Gypsum molecules consist of two parts water and one part calcium sulfate, giving the compound its unique properties. Although gypsum contains 21% water by weight, nearly 50% of it is water by volume.

Gypsum remains dry because the water in it is crystalline. Unlike ice, which melts at room temperature, this water stays solid unless heated to 212°F, at which point it turns gaseous and evaporates.

Historical Uses of Gypsum

The Greeks referred to gypsum as "gypsos," recognizing its versatility. While pure gypsum is white, impurities can color it gray, brown, pink, or black. Assyrians used a variant called alabaster for sculptures. Today, finely ground gypsum has numerous applications, including an ingredient in toothpaste, a filler in paints and cosmetics, and a base for polishing automotive glass. It's also used in agriculture as a fertilizer and in food products as a calcium source, and even in movies to simulate snow.

When heated to remove much of its water content, gypsum becomes plaster of Paris, a fine white powder that can be molded when mixed with water and retains its rock-like qualities once dried. Apart from making drywall, this material is useful for sculptures, pottery, and medical casts.

In North America, millions of tons of gypsum are mined annually to produce gypsum board. Up to 20% of gypsum used in drywall can be recycled from waste produced at plants or construction sites. Moreover, electric power plants that produce gypsum as a byproduct of flue-gas desulfurization provide an economical, eco-friendly raw material for high-quality gypsum board.

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The Manufacturing Process

The making of drywall involves combining gypsum core material with two layers of paper, drying it, and then cutting it into standard panels.

Blending of Additives

• 1 Depending on the type of drywall being produced, various additives are mixed with plaster of Paris, which forms the core. Additives like starch ensure paper adherence, paper pulp adds tensile strength, unexpanded vermiculite enhances fire resistance, and substances like clay can be added. Additionally, water is mixed to form a slurry of appropriate consistency.
• 2 An asphalt or wax emulsion is included to control moisture resistance. A foaming agent introduces air into the mixture, making the gypsum board lightweight and easy to handle. In cases where fire resistance is required, glass fibers are added to the mixture.

Making the Sandwich

• 3 The gypsum slurry is poured between two layers of paper. This "sandwich" then moves through rollers to compact the core to the desired thickness, typically 9.5 mm, 12.7 mm, or 15.7 mm.

Finishing the Edges

• 4 Automated production lines in gypsum plants, ranging up to 247 meters long, shape the drywall edges as the board moves along the conveyor. Edge shapes vary and include options like square, tapered, beveled, or rounded.
• 5 The face paper wraps around the edges to seal them to the back paper.

Cutting the Panels

• 6 Once the core sets, the continuous strip is sliced into standard panels sizes—typically 1219 mm or 1572 mm wide and 2400 mm or 3600 mm long.

The Drying Process

• 7 The panels then go through a lengthy drying oven. For example, one gas-fired oven measures 143 meters long, starting at 500°F and gradually reducing temperature over 35-40 minutes. Both humidity and temperature are meticulously controlled.

The Finished Product

• 8 Post-drying, the panels undergo visual inspections before being bundled into sets of 30 or 40 and stored in a warehouse awaiting shipment. Each board is labeled for inventory control, billing, and retail price scanning.

Product Evolution

Since its invention, gypsum board has undergone improvements, becoming lighter and better-performing. Initially weighing 2 pounds per square foot, modern gypsum board weighs around 1.6 pounds per square foot, facilitating easier handling and reducing shipping costs.

Fire-resistant and moisture-resistant types were introduced in the late 1950s, followed by controlled density (CD) ceiling board in 1988. Research is ongoing on better disposal methods for wallboard waste, with studies analyzing the reuse of construction scraps in agricultural applications.

Where To Learn More

Periodicals

"TU Electric Pioneers FGD-Gypsum Production for Use in Wallboard." Power, April 1988, pp. 33-34.

White, Edwin H. and Mark E. Burger. "Construction Drywall as a Soil Amendment." BioCycle, July 1993, pp. 70-71.

Other

Standing, H.A. "The Story of Gypsum." Domtar Gypsum Company, 1-800-DOM-TAR1.

—Loretta Hall

Feasibility Study For Gypsum Powder Manufacturing | PDF

This document is a business plan for a proposed gypsum powder manufacturing plant by AMX Manufacturing PLC in Ayshea, Ethiopia. The plant aims to produce 150,000 tons of gypsum powder annually, utilizing abundant local gypsum resources, and create over 200 jobs. It will cost approximately 140 million Birr to establish, and is projected to have an IRR of 42% and payback period of 1.5 years. The plant will help meet domestic and export demand for gypsum and substitute imports, while generating economic benefits and foreign exchange for Ethiopia.

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