Gypsum board

Gypsum board, also known as sheetrock or drywall, is a panel of noncombustible gypsum core that is usually encased in paper. The paper face extends around the long side to protect the core while reinforcing the product. Edges can be squared, rounded, and tapered which can allow for reinforcement and concealing with tape. It is lightweight and resists fire. Gypsum board also conducts little heat or sound. It is noted for being easy to install and is generally vermin proof.

History
Augustine Sackett was the first to patent gypsum board. The board measures 32 by 36 inches and had six layers of unsized felt paper that separated five layers of gypsum. Gypsum board traditionally weighed 1 ½ pounds per square inch. Sackett Wall Board Company first introduced Sackett Board in 1898. Sackett Board had four sheets of paper and three sheets of gypsum. This board was marketed as being a replacement for lath and plaster but was commonly used as a backing surface that plaster was applied to. Ten years later, Stephen Kelley began Samson Plaster Board Company and soon patented a process for making 32 by 36 inch two-ply boards, replacing felt paper with chip paper. Soon after, the United States Gypsum Company acquired the Sackett Wall Board Company and the Samson Plaster Board Company in New Jersey. The following year, the company took over the Lockwood Paper Company and produced its own paper for gypsum board. United States Gypsum Company’s engineer, Clarence Utzman, found a way to make the gypsum board with folded paper edges. John and Joseph Schumacher invented successfully developed a method of producing boards faced with paper that were cut uniformly and could hinder permeation. With a standard for creating gypsum board and a production line, the amount of gypsum board produced before World War I grew extensively. Military barracks used gypsum board to replace flammable fiberboards. Gypsum board was less expensive that wood and metal lath for plaster backing as well. United States Gypsum introduced a wide variety of gypsum building boards in the 1920s, including Sheetrock wallboard and tile board, Rocklath, and Gyp-lap sheathing. These materials cut down on the cost of construction. These boards were commonly 32 to 48 inches wide and normally 3/8 inch thick. Attaching Sheetrock gypsum board to an interior support member resulted in a finished wall. Demand for gypsum grew significantly during World War II when drywall became the preferred building material to plastering. Gypsum as a substitute building material in war housing showed it potential. Gypsum’s popularity seemed to explode after the war, when the need for housing increased. Gypsum has undergone some improvements since its introduction. It has improved strength and reduced weight, which makes installation easier. Gypsum underwent several experiments in the 1920s, testing different fillers and microscopic bubbles (which led to a lighter wallboard). The National Gypsum Company patented Gold Bond as the name for this new gypsum board. Gypsum board underwent many improvements to the surface and how it was finished. Early products used heavy unsized paper to face the product which was replaced by recycled newspaper that was less permeable. Wood veneer finishes were marketed in 1937 as well as decorative pastel surfaces followed with vapor retarding foil insulating layers in the 1940s. Vinyl covered boards were introduced in the 1950s and required no further decoration. Gypsum board had always been known for its fire-retarding qualities. Later improvements, adding multiple layers to wallboard, seemed to improve these qualities. The 1940s were full of research that produced special additives like asbestos or mineral wood that enabled fire-retarding wall systems that had fewer layers. Certain-Teed Products introduced the first fire-rated gypsum board in 1946. Later, Bestwall Firestop was introduced. Bestwall Firestop had small amounts of glass fibers and unexpanded vermiculite that helped retain strength and shape after the chemically bound water was driven off by extreme heat. Fire-rated gypsum became a standard product for most companies by the 1950s.

Manufacturing Process
Gypsum is found around the world in its natural state of a grayish white rock. 90% of the amount mined is used for building materials. During the manufacturing process, the gypsum will be quarried and crushed until it is a fine powder. Ground gypsum is placed into a calcining kettle and heated, causing more than 75 percent of its water to evaporate. While the material is heated, a rotating shaft agitates the material. The heated material is mixed with starch and retarder in a mixer and then fed down a 4-foot wide conveyor belt that runs through a water reservoir. The mixture absorbs just enough water to make slurry. The mixture then travels through a mixer that is coned shaped with a propeller styled mixing device. The mixture is poured onto a piece of paper that is on a forming table. The mixture is covered with a piece of paper and passed through rollers where heaters are used to set the plaster edges. The paper adheres to the mixture; the edges of the paper are scored, and then folded over. The gypsum mixture begins to cure and is moved to an automatic cutter. The board is cut and partially set, then moved by a conveyor to a dryer to finish curing. Wall-board is commonly twin mounted (two boards face each other with the edges taped together).

Uses and Installation
Gypsum board was a popular material for drywall construction because it did not need several weeks to allow layers of plaster to dry. Gypsum board came ready to finish within hours. The fireproof qualities helped make it more desirable, as did the inexpensive cost. Gypsum board was inexpensive because the natural materials were so readily available regardless of location. World War II saw a rise in use in commercial, industrial, and residential applications. Sheetrock and Sheetrock wallboards found countless uses as walls, wainscoting, ceilings, and partitions. Installation methods have varied slightly over the years but have centered on two basic methods for single-layer application-horizontal and vertical. In either application, the boards are attached directly to the studs in the interior of a building. The framing should not be less than 16 inches on center with header strips inserted for support. Ceilings should be at right angles to the joists, with joints staggered. Wall boards should be hung from the ceiling first. Nails should not be less than 3/8 inch from the edge and should be started first at intermediate supports, second to edges. The nail head should be just slightly under the surface. The nail should always be driven straight in. Drywall screws are offered according to what material it will be driven in to. Wood screws should go at least 5/8 inch into the wood while metal framing screws should penetrate 3/8 inch. Joints should be covered with reinforcing tape and joint adhesives or cement. The cement should be spread over the nail heads. Tape is meant to cover joints and should be placed over the center and pressed into the cement. A thin coat of cement is applied over the surface of the tape to hide it. The edge of the cement should be feathered to blend with the surrounding wall. Nail holes should be filled until they are flush with the surface. After drying, excess material can be sanded lightly to match the surrounding area. Interior corners require the cement to be spread on each side while the tape is folded along the center and pressed in at an angle. This should be allowed to dry before additional coats are applied. Outer corners require a metal corner that can be tacked or bent into place, then covered with several coats of joint cement on each side. Different methods for installation have been developed in an attempt to smooth the finished wall. The early 1900s had boars that had round, folded edges to provide reinforcement for nailing edges. Square folded edges were introduced. Square edges allowed for the boards to fit more closely together. Tongue and groove edges were later introduced to help eliminate ridging. 1937 introduced a wallboard with recessed edges that would create a valley where the two pieces came together. This valley allowed for a flat, smooth joint treatment. The tapered edge was introduced in the 1950s and is still being used today. Specialized nails were eventually replaced with drywall screws that had different points and threads. Joint tape was once perforated paper tape but has recently been replaced by metal strips and self-adhering fiber tape.