April 15, 2011

Drywall, plasterboard, or gypsum board – whatever you call it, this ubiquitous building material comes in panels made of gypsum plaster sandwiched between sheets of fiberglass or thick paper. The interior walls and ceilings of innumerable buildings are comprised of drywall. Clearly, we’ve come a long way since ancient Egypt, when constructing a home meant mixing mud and chopped straw, putting the mixture in molds, and baking it into bricks in the sun.

Drywall is much more convenient than spreading plaster on lath-work and then adding a finish. After all, drywall has to be finished by hand only at the fasteners and joints. Consequently, it doesn’t require nearly as much work, or time to dry, as more antiquated methods.

The first drywall prototype came into being in 1894, when Augustine Sackett put plaster between four layers of wood felt paper and called the result Sackett board. It wasn’t until the first quarter of the 20th century, between 1910 and 1930, that true gypsum board was invented. It was similar to modern drywall, in both its general structure and its resistance to fire. Down the line, manufacturers added air bubbles to the plaster to make gypsum board less heavy.

The next development in drywall’s evolution was the use of rock lath – compressed gypsum plaster board – rather than wood or metal lath. This product was soon faced with paper that had gypsum crystals in it. The crystals bonded with wet plaster, making the gypsum board even easier to use.

Today, drywall consists of a gypsum plaster core inside a paper liner. (Gypsum’s chemical name is calcium sulfate dihydrate, which can also be written CaSO4•2H2O.) To ensure that drywall can resist fire and fungus, manufacturers add vermiculite, fiberglass, or similar materials. Drywall liner itself can be made of fiberglass instead of heavy paper. When drywall is produced en masse, it’s generally dried in kilns.

American drywall panels tend to be 4 feet wide and either a half-inch or five-eighths of an inch thick. (Panels can be long or short, depending on their purpose.) Drywall prevents heat from moving between rooms (thermal resistance), and it does the same with sound. It’s possible to install drywall in a home within a day or two, and seasoned non-professionals can generally do it without difficulty.

Installers use a T-square to cut drywall panels into the right sizes and shapes, whereas a keyhole saw is best for making small holes, like an opening for a light switch. To attach drywall to a wall, you need nails, glue, or drywall screws. It’s important to secure each panel to a wall stud or ceiling joint, and joint tape or compound can hide the seam between one panel and the next. If compound is used, it should be sanded smooth after it dries.

Water is no friend of drywall. It can make panel swell, mold, or fall apart. In hot, humid climes, greenboard or cement board, both resistant to moisture, are commonly used. Gypsum’s built-in hydrates minimize the amount of heat that can travel through drywall, and the gypsum in “Type X” drywall includes glass fibers, which makes it especially fire-resistant.

The typical U.S. home has more than 7.31 metric tons of gypsum in it. Compared to other continents, North America uses an extraordinary amount of drywall. Fortunately, EcoRock, an environmentally friendly drywall made of recycled kiln dust, slag, and other waste products is becoming increasingly popular.

After 2000, some drywall made in China was full of volatile chemicals. Under certain circumstances, such as heat and/or humidity, these chemicals – among them carbon disulfide, carbonyl sulfide, and hydrogen sulfide – could emerge as gases. They left copper and silver black and powdery, due to the interaction between those metals and the gases’ sulfurous components.

In affected homes, then, copper and silver items worked like canaries in a coal mine, letting residents know that something was amiss. The harmful chemicals from tainted drywall caused breathing problems, nausea, headaches, sinus difficulties, eye irritation, and other unpleasant symptoms, and their potential long-term effects included insomnia, fatigue, and memory loss.

After the Florida hurricanes of 2004 and 2005, and especially following Hurricane Katrina in 2005, the U.S. purchased a great deal of drywall from China. Repairing the hurricane damage depleted America’s drywall supply, making Chinese drywall a must. Since the beginning of 2006, the U.S. has imported more than 550 million pounds of drywall manufactured in China.

Contaminated drywall has to be replaced, of course, but so do any copper wires or pipes that it has affected. In the U.S. alone, between 60,000 and 100,000 homes contain bad drywall. While most of the Chinese drywall’s makers remain anonymous, the company Knauf Plasterboard Tianjin Co. Ltd. prints its name on every panel it produces. For this reason, Knauf has become the main target of class-action lawsuits since 2009, when Congress demanded an investigation of the Chinese drywall problem.

The study concluded that pyrite, which abounded in the tainted drywall, was almost certainly the cause of all the trouble. Scientists believe that the sulfurous gases emerged via pyrite oxidation, and that the pyrite’s ultimate source was fly ash. While American drywall makers also use fly ash, they must adhere to strict safety standards. The bad Chinese drywall was so poorly made that pyrite oxidation was able to occur.

At present, Knauf has begun the process of remediation – that is, removing and replacing tainted drywall and damaged metal in hundreds of homes. This action was the direct result of a class-action lawsuit by a group of Florida homeowners. The suit also names suppliers and builders who provided and installed the drywall in question. While many more homes might contain contaminated drywall, and not all of the wrongdoers will end up paying for their negligence, some justice has clearly been done.


  1. [...] video is a demonstration of a drywall [...]

Previous post:

Next post: