PLYWOOD: Lurid Tales of Grains and Glues
nyone who has ever used a pair of disposable chopsticks understands the problem that plywood is designed to address: when you pull the two sticks apart, the isthmus joining them breaks with a satisfying snap. In general, all wood is like that much stronger across its grain than parallel to it. Thin pieces are flexible and light, but they can scarcely hold any weight.
The ancients knew this, too, and developed a crude form of what we know as plywood. Their solution, dating back to the tombs of second millennium B.C. Egyptian pharaohs, was to glue thin slabs of wood together with their grain running perpendicular to each other. The strength of one ply compensated for the weakness in the next. Similar ventures are known from ancient Rome, China and 17th century France.
It wasn't until the Industrial Revolution met the great forests of the Pacific Northwest, however, that plywood made its mass-market debut. The prototype panels were trotted out for the 1905 World's Fair in Portland, produced one at a time, clamped with house jacks and held together with animal glue which stank so bad that the workers had to leave the mill frequently in search of fresh air. Since then, plywood has become so widely used that in 1995 enough was produced worldwide to cover a football field to a depth of eight miles. About two-thirds of that is used in just three countries: the United States, China and Japan.
The process of making plywood has become ever more sophisticated. To start with, logs are cut to lengths of eight-and-a-half feet, stripped of their bark and steamed to soften the wood. Next, they are mounted on a lathe and spun at a few hundred revolutions per minute. A sharp knife peels the spinning log into a single running strip of veneer between one-tenth and one-quarter of an inch thick, depending on the kind of plywood being made. The process is so quick that a medium-sized log, some two feet in diameter, can be reduced to about 400 feet of tenth-inch veneer in a matter of ten or fifteen seconds.
Because the log is sliced with a knife, none of it is lost to sawdust, although some is wasted in the process of reducing an irregularly shaped log to a true cylinder. Over time, systems have improved to discard less and less of the center core at the end of the process. Previously, veneer lathes would stop peeling when the remaining core was just large enough to make a pair of two-by-fours or a fence post. New technologies allow veneer-makers to peel logs down to a core barely thicker than a broomstick.
Once veneers are made and trimmed to standard lengths, they must be handled carefully so they don't tear. The sheets are dried in a kiln, and some are then patched. Higher grades of plywood must have all their knots cut out and plugged with any of the standard-sized wood patches, such as the familiar football- or eye-shaped repair.
The sheets of veneer are then laid up in stacks and glued, with the better-looking veneers on the face and back, and the unappealing, irregular or knottiest sheets in the center. The glued sheets almost all made in the familiar four-by-eight-foot size are then sandwiched for about five minutes in a hot press. Some final repairs are made with resin, the panel is sanded, and it's ready for use.
The last twenty years have seen significant changes in the raw materials used to manufacture softwood plywood. At the outset, the western plywood industry relied heavily on large, flawless old-growth Douglas fir logs. These trees yielded lots of near-perfect veneer, providing panels unmarred by knots or patches. But as top-notch trees have become scarcer, they are in greater demand for solid lumber that is clear of knots, or as standing forests to provide habitat for the spotted owl, marbled murrelet and coho salmon. The industry adjusted by retooling for smaller logs, and customers adapted by reconciling themselves to knot repairs in their plywood. Where softwood plywood was once made from six-foot-diameter logs, now it comes primarily from logs that are at most two feet across.
At the same time, much of the U.S. softwood plywood industry has shifted from the Pacific Northwest to the South and Southeast, where pine plantations abound on private lands. These small pines produce a lower quality panel than older trees, according to forestry consultant Dobbin McNatt, who recently retired from a 33-year career at the U.S. Forest Service Forest Products Laboratory in Madison, Wisconsin. These southern pines are typically cut by the time they hit 30 years old, and are made up in large part of "juvenile wood," he explains, which is more prone to warping than older fibers. "I've seen it put down as underlayment for a floor in real dry conditions in the winter and then turn wavy in the summer," he says.
The wood products industry responded in still another way to the declining supply of large logs. In the process, they also dealt with the labor-intensive nature of conventional plywood production. They developed a panel called "oriented strand board" (OSB), made up of layers of wood chips about 3 or 4 inches long by 1 or 2 inches wide. Successive layers are arranged with the grain running perpendicular, just like plywood veneers. Machines deposit these very uniform chips on a form, add glue, and press a fluffy stack that might start out 6 or 8 inches tall to a thickness of less than half an inch. OSB does for structural panels what press logs do for firewood: provides a way to manufacture an absolutely uniform product with lots of machinery and little hands-on labor. Where a plywood mill might employ a couple of hundred people, there might be just three or four on an OSB plant's shop floor. It also allows the industry to make structural panels out of hitherto less-exploited species such as aspen. These differences are reflected in the price, too: about half the cost of comparable plywood products. As a result, OSB has grown from a relatively small business in the early 1980s to nearly two-thirds the volume of the plywood industry in 1996.
But OSB can't take the place of plywood in all situations. Apart from aesthetic concerns, it can't tolerate outdoor exposure the way plywood siding can. Louisiana-Pacific discovered this in the early and mid-1990s when it marketed Inner Seal, a brand of OSB siding. The resin-treated coating that was supposed to protect it from the elements failed, and the panels began to crumble. L-P spent tens of millions of dollars settling suits by homeowners whose siding disintegrated, leading to the ouster of chairman and president Harry Merlo in 1995.
Probably the most celebrated plywood cause has been the logging of rainforests in Southeast Asia particularly Malaysia and Indonesia to create a product that is thrown away after a short time. Lauan is a group of heavily used tropical tree species used to make plywood. Lauan plywood is used extensively in Japan, both for concrete forms and for cheap furniture, often discarded after a few years. It has also been a favorite of Hollywood set builders, who used to go through a quarter of a million sheets of lauan plywood each year. Some studios such as MCA/Universal and Paramount have recently shifted to ecologically sounder substitutes; others, such as Disney and Warner Brothers, have cut back significantly on their use of lauan. Indonesia and Malaysia remain the second and fifth largest makers of plywood in the world; Malaysia would place higher if the logs it exports for plywood manufacture elsewhere were included.
In some parts of the tropics, such as the Amazon, most logging is a by-product of other economic pressures to clear land for ranching, or build mining roads. But in Southeast Asia, logging is the main force driving the clearing of the rainforest and the displacement of peoples such as the Penan of Sarawak in Malaysia.
The Rainforest Alliance operates a certification program called Smart Wood to distinguish sustainably harvested forest products which originate from temperate as well as tropical regions. Certifiers consider the entire management system of a forest in deciding whether to award their stamp of approval, from logging techniques to fair labor practices.
Smart Wood recognizes at least two plywood suppliers. Plywood and Lumber Sales in Emeryville, California (510/547-7257) offers top-grade cherry and red oak panels, in sustainably harvested veneer glued onto a core made of North Dakota wheat straw. These panels will sell to cabinetmakers for about $130 or so, compared with the $85 for a comparable run-of-the-mill panel. Wisconsin's Marion Plywood Corporation (715/754-5231) offers plywood made from the certified Menominee Tribal Enterprises hard maple, yellow birch and red oak.
A variety of panels made from post-consumer waste is available. Homasote is made from discarded paper, which is pulped and then formed into boards. Homasote, which has been in use since 1916, comes in styles suitable for roof decking, subflooring, sheathing and interior design. Unicore is a similar product, which Universal Studios has just adopted for its set construction.
|Reprinted from the The Liberty Tree Alliance Website, www.libertytree.org. Liberty tree is a national association of writers, scientists, and activists concerned with the preservation of the natural world. Liberty Tree Alliance, 1140 Broadway, Suite 1205, New York, NY, 10001; (212) 683-1226; email: libertytreeigc.org|