How Drywall Works

The U.S. Gypsum Company (USG) invented drywall in 1916. It was originally called "Sackett Board," after the Sackett plaster company, a USG subsidiary [Source: Allen]. The material was first sold in the form of small, fireproof tiles, but within a few years, it was sold in multi-layer gypsum and paper sheets. In less then a decade, it took on the form we know, consisting of a single layer of compressed gypsum sandwiched between two sheets of heavy paper.

While it only took a few years for this board to evolve into the material we know today, it took 25 years for builders to begin using drywall in any substantial quantity.

With all its uses and benefits, why were builders hesitant to use something as simple as drywall? At the time, drywall was thought of as a cheap fix, with none of the fine art associated with making plaster. People didn't want to live in homes that were shoddily constructed, so they stuck with the tradition and expense of plaster.

U.S. Gypsum eventually changed the brand name of the material to "Sheetrock" in an attempt to improve drywall's reputation, but builders and homeowners still paid no attention.

It wasn't until the United States became involved in World War II that builders came around to the benefits of using drywall [Source: Gellner]. As the country's labor force became focused on war manufacturing and many soldiers were sent overseas to fight, quick and inexpensive building materials were needed to offset the labor shortage and war costs. Because the labor shortage was too intense for plastering to remain a viable building option, people began to use drywall instead. Houses and factories could be constructed in a fraction of the time and with a fraction of the labor previously required. Cheap and efficient products were seen as patriotic because they allowed citizens to spend more time and money supporting the war effort.

By the time the war ended in 1945, drywall had become the dominant building material in the United States. During the post-war building boom, contractors knew they could construct homes and workplaces in one-tenth the time if they abandoned plaster for drywall, leading to higher profits. Over time, the use of plaster gradually faded as people all over the world turned to drywall. With net sales of over $5 billion in 2007, the U.S. Gypsum Company is still one of the world's top producers and innovators of drywall and related products [source: USG].

Next we'll look at how drywall is made and how it's evolved since the early days of its invention.

Drywall is made primarily of gypsum. Gypsum is a mineral usually found in massive beds that look like white sand, though impurities can cause beds to appear pink, yellow or gray. One of the most famous gypsum beds in the United States is the popular White Sands National Monument in New Mexico.

Despite being used to make drywall, there's a large amount of water in gypsum. The water is in crystalline form, which is why the individual molecules of gypsum are dry. These crystalline water molecules give finished drywall its fire-resistance. As drywall gets hot, the water crystals begin to destabilize and begin vaporizing as the water reaches its boiling point. The evaporating water crystals keep the drywall cool, protecting the structure behind it.

Once gypsum has been mined, it's transported to factories throughout the world. There, raw gypsum is mixed with several additives, including starch, paper pulp and an emulsifier (or thickening agent), then blended with water to form a thick paste. The gypsum paste is spread onto Manila paper in 3/8-inch to 3/4-inch-thick layers. Another sheet of Manila paper is then laid on top. The entire formation passes through ovens that heat the sheet at temperatures up to 500 degrees Fahrenheit. This dries the material out and prepares it for cutting. Typical sheets are 4x8 feet, though 4x10 feet and 4x12 feet sheets have become popular recently, as they allow for faster installation of taller walls.

Additional additives or types of paper are used when creating more specialized forms of drywall. For more on this, and information on finding the right type of drywall to suit your needs, read on to the next section.

While regular drywall is appropriate for most applications, there are many other types that are better suited for special circumstances. The chart below will help you choose the correct type for your application.

­Once you've determined which type is best for your project, you'll need to figure out how much you'll need. Measure the square footage of the walls and ceilings you need to cover. To accommodate for material waste due to cutting and size restrictions, add 20 percent to your measurement. Divide your square foot measurement by 32 feet (the size of the typical sheet) to find out how many sheets you'll need to purchase.

Of course, no matter which type of drywall you use, it's no good on its own. Joint compound, often called “mud” or “spackle,” goes hand in hand with drywall. It's made from a mixture of limestone, emulsifiers, various polymers, and water. Its smooth texture makes it easy to apply, sand and blend to create an even finish. Because joint compound typically takes about a day to dry, fast setting mixes are available. Drywall mud is typically applied over fiber-mesh or paper drywall tape. This tape is used to close up and tighten seams that occur when drywall sheets are hung side by side.

To find out which tools are useful for drywalling, let's take a look at how drywall installation works.

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Drywall installation is a popular DIY project for homeowners because it's easy to learn and doesn't require any expensive specialty tools.

To begin installing drywall in your home, use the chart in the previous section to determine which kind of drywall you need for your project, then estimate how many sheets you'll need based on the size of the area. Most home improvement stores will deliver your purchases to your home, which is useful because of the length of the drywall sheets. You can also save cash by renting many of these tools. Once you've made your purchase or rental, you can break your project down into three easy steps:

1. Cutting

Begin by laying your drywall sheets out on a level, dry surface. Measure the length you'll need for your project, and use a pencil to mark where you'll need to cut the sheet. Using a T-square as a guide, cut the sheet along the marks using a drywall saw. You can make most of your cuts before starting the project to ready your materials, or you can cut pieces as you work. The latter method results in fewer mistakes and less waste, but may take more time. A keyhole saw can be helpful for cutting spaces for electrical outlets and light switches, and a circle cutter is useful if you have curved spaces to work with.

2. Hanging

Start attaching your drywall sheets to the wood or metal studs used to frame your space. You should hang sheets horizontally when working with wood studs, while metal studs work better with vertical installations. This is because wood studs are more likely to warp and deflect over time. Hanging the sheet horizontally allows each sheet to be in contact with more studs and helps minimize deflection. Generally speaking, it can be more difficult to screw into metal studs. When using wood studs, you should also apply a drywall adhesive to the face of the studs before hanging your drywall in order to further minimize deflection. To attach the drywall to the studs, use a screw gun and drywall screws, making sure you hit the studs. Screws should be placed about every four inches.

3. Finishing

­Finally, you'll tape, sand and finish the drywall. This involves applying three layers of mud, one layer of drywall tape, and a whole lot of sandpaper. First, use a 6-inch finishing knife to spread joint compound along each seam. This first layer is called the tape coat, and should be about four inches wide, centered on the joints in your drywall sheets. Next, apply drywall tape along the joints. The mud you applied will hold it in place. Your second coat of mud is called your block coat. Use your 6-inch finish knife to apply a second coat of mud on top of your drywall tape. Use just enough to seal the drywall tape in place. The final coat is called the skim coat. A 10-or 12-inch knife should be used to apply a third coat of mud. Take your time on this coat to spread the mud thinly away from the seams to provide a smooth, level surface.

Now, the waiting game begins. Allow 24 hours for the mud to dry to begin sanding.

Use a pole sander and 120-grit sandpaper to lightly sand the mud you applied earlier. You've finished sanding when you can't see any tape or mud bulges on the walls' surface, and when a level applied to the wall shows it is smooth and even. Wear a mask and goggles while sanding to prevent damage to eyes and lungs.

Sometimes drywall will become damaged due to impact from people or objects. This damage is simple to repair, and simply involves filling any holes, then covering them with mud and sanding them so they are smooth and flush with the rest of the wall. For larger holes, cut out a piece of drywall that will roughly fill the hole, then fill the rest of the space with mud. For smaller holes or dings, mud can be used on its own to fill in the damaged area. After you've filled the hole, use a single coat of mud and sand as usual.

Still not sold on drywall? You can find some alternatives on the next page.

As useful as drywall is, it still has some drawbacks. Many people are turned off by the hollow thump made when you knock or tap on a wall built with drywall. It can remind people that drywall is still a cheap, quick fix. Another problem is drywall's lack of texture and character, as well as its inability to be molded. Finally, some people feel that drywall is too susceptible to damage.

Luckily, there are several alternatives to traditional drywall that can be used to create walls in a building's interior. We'll take a look at some of them here:

Next we'll look at how drywall fits into today's green building trends and examine ways drywall can be recycled by both the manufacturer and the end user.

Nothing's hotter in construction these days than sustainable, environmentally friendly design. Fortunately, drywall is easy to recycle and is made of green and recycled materials.

From a manufacturing standpoint, drywall is already pretty eco-friendly. The cores are made from 90 to 95 percent recycled material, mostly reclaimed drywall, while the paper exterior is made exclusively from 100 percent recycled content, mostly old newspapers. From an emissions standpoint, however, the drywall industry still has a way to go. Approximately 1 percent of U.S. energy emissions come from the production of drywall [Source: Sassoon]. A product called EcoRock, introduced in 2008 by San Jose-based Serious Materials, is said to be the first zero emissions drywall material on the market. Essentially, it has no carbon footprint and is still made from nearly 100 percent recycled content. Builders are showing interest in this product, but time will tell if people will be willing to pay a premium for reduced carbon emissions.

­For the consumer, drywall waste is 100% recyclable, but finding places to recycle drywall can be tricky. With commercial use, manufacturers have programs in place so builders can return scrap drywall to be recycled. For homeowners, recycling drywall is a bit more difficult. Many cities and municipalities have drywall recycling programs in place, but finding them may require a bit of research. USG is scheduled to open a gypsum recycling plant in Washingtonville, Pennsylvania in 2008. This plant will be the largest of its kind in the world, and as green building continues to grow in popularity, additional channels for recycling will become available.

Recycled drywall has three major uses. The first is to crush the material and use it to make new drywall. This is currently the most popular choice by far, and all of the major manufacturers have systems in place to do so. Recycled drywall can also be used an an ingredient in Portland cement, which is used to make stucco, plaster, and other building materials. Finally, crushed drywall is growing in popularity in the agricultural world. It is useful as a soil conditioner, providing calcium and sulfur for plants, which is especially useful when growing peanuts, potatoes, or corn. Recycled drywall can also be placed on soil that has a high salt content to help neutralize the ground so that crops can eventually grow there.

It took some time for the building industry to recognize drywall for what it is - an extremely versatile, inexpensive and sustainable material that has overcome its initial reputation as a cheap substitute for plaster to become something an average person could use to build walls. Not bad for a quick fix.

For more information on drywall, please see the links on the following page.