All Aboard With Optibor^TM TG Boric Acid
November 1999

With residential and commercial building proceeding at a blistering pace in North America, there has been skyrocketing demand for wallboard this year. Wallboard (also known as plasterboard or gypsum board) plants are operating 24 hours a day, seven days a week and are still unable to meet the demand. The shortages in the southeast United States are so acute that they have been importing board from Norway. Building contractors have been sneaking into do-it-yourself supply stores, willing to pay retail prices for boards, but only to find purchases rationed to a few dozen per customer.

How did this situation come about? There has not been a new plant constructed in North America in the last ten years, and manufacturers, who had been badly hurt in the past by increasing capacities only to have been hit by recession, have been cautious. How can manufacturers increase line speeds and production to meet demand, and maintain product quality? The answer: by the addition of Borax's Optibor TG boric acid. Optibor TG increases the productivity in the process, saves in raw material, energy and shipping costs, and improves the overall board quality.

With North American wallboard plants operating at full capacity, and not meeting demand, plans have been announced for the addition of eight new plants in North America by 2003. With these new plants, capacity will be raised by 30 percent. All the plants currently being designed or under construction in the U.S. will use synthetic gypsum from power plants. The technology is essentially the same as for natural gypsum, but the handling is slightly different.

Wallboard basics

Making wallboard appears simple, but it is actually quite technically demanding. The process starts by taking gypsum, chemically known as calcium sulfate dihydrate (CaSO4·2H2O) and calcining it to convert it to plaster (often referred to as "stucco", but not the same material as used on the outside of buildings).

Calcium sulfate hemihydrate (CaSO4·1/2 H2O) is the chemical form of plaster (stucco). This material is mixed with water and various additives and squirted onto a moving sheet of paper. The slurry then passes through a roll and is covered with more paper. It travels further down rollers where it hardens, is cut into appropriate lengths, and goes through a dryer to remove excess water.

It is interesting to note that gypsum, unlike cement, is a physical structure rather than a chemical structure. The needle-like gypsum crystals form a network to give the board its physical integrity.

The trend in board making in North America has been towards lighter and lighter boards. There are many reasons for this, but probably the two main reasons are ease of handling during installation, and shipping costs. Shipping costs are quite significant for wallboard, as it is a high weight product with relatively low value. While the advantages of lightweight boards are many, making a quality lightweight board is not simple.

Lighter weight means less gypsum in the board as a whole, and in particular less gypsum at the paper/core interface and at the edges and ends. The less gypsum at the interface, the easier it is to over-dry or calcine the surface. When the gypsum crystals at the surface are calcined (converted back into their hemihydrate form), they lose their strength and the bond between the gypsum and the paper can fail. Obviously this 'splitting' is a serious quality issue. Over-drying of the ends ('end burn') and edges can also be a problem, and can lead to crumbling during handling and nailing.

Humidified deflection or 'sag' is another problem related to lightweight boards in ceiling applications. This can be a problem particularly in humid environments. The gypsum needles when wet can become 'lubricated' and slip over each other in response to gravity. Other properties related to the perimeter and surface of the board are referred to as edge hardness and nail-pull resistance. These properties measure how robust the board is to handling both in the manufacturing process and during installation, and are related to the strength of the board near the surface, edges, and ends. This is in areas where the board is most likely to be calcined during drying.

The Optibor TG solution

Using Optibor TG as an additive can address all of these problems related to lightweight boards. It effectively raises the calcination temperature for gypsum, thereby protecting the wallboard from the effects of over-drying. Water soluble Optibor TG migrates to the surface of the board (as well as the ends and edges) during the drying process, forming a very thin but concentrated layer. It effectively increases the density of the core at the interface with the paper, but without increasing the overall weight of the board. This dense layer is resistant to over-drying. The added layer of protection allows the boards to be processed more rapidly through a hotter dryer, thus speeding up production.

Increasing starch content can also serve to protect the gypsum crystals from over-drying, but since starch holds water so tightly more energy is required to remove the water from the board, increasing drying times and energy costs. Optibor TG also modifies the gypsum crystals, making them larger and thicker. This contributes to the rigidity of the boards, reducing the sagging tendency.

While gypsum board makers are working hard to keep up with the demand, Borax's Optibor TG is doing its part by providing increased production rates while maintaining product quality.

The above information was adapted from the article 'Effects of Boric Acid on Gypsum Board' in the June 1999 issue of Global Gypsum by Bob McBroom and Alona Vizel. Bob is principal research chemist at U.S. Borax in Valencia, California.