Botanical Engineering
Building better with borates
October 1998

In its natural state, wood is remarkable. Species like balsa are renowned for lightness; black ironwood is so heavy it sinks. Weight for weight, constructional timber is several times stronger than steel. It has been a friend to carpenters, joiners and builders over the centuries because of its versatility, physical properties and ease of working.

But there are downsides. Wood's very popularity raises questions about the logging and sustainability of old-growth forests. Being a natural material, it is also prone to attack from fungi. This, then, is the story of old technologies, new technologies, and of Borax Borogard® ZB wood preservative making a valuable contribution to the sustainability of our forest resources.

Improving on the natural product is nowhere near new. The history goes back to ancient Egypt, where veneers were used to beautify domestic and tomb furniture. Our modern plywood is a close relation, and Oriented Strand Board (OSB), made from wood chips bonded together, is another of this family of natural wood composites known as engineered woods. With OSB, planks and sheets can be re-created with dimensions far larger than a sawn tree, and with better properties than the parent material. It is mechanically excellent, strong, consistent, easy to install and work, and is a popular material in house construction as exterior siding, sheathing, and as flooring and roofing.

In our environmentally-conscious world, wood for construction offers an impressive pedigree. It is the only renewable building material. It is also the most energy efficient. While it represents almost half of all industrial raw materials used in the U.S., it consumes just four percent of the energy needed to produce these materials.

And sustainability? The debate about renewable forestry hinges not only on the logging versus new growth ratio, but the species need to be considered too. Highly-desirable hardwood timbers like oak and ash grow relatively slowly, and only a quarter of the volume of felled trees like these can be used to provide solid sawn lumber.

But there are also the fast-growing but hitherto under-utilized 'weed' trees like the Great Lakes aspen and it is in this area that the engineering of wood is making its sustainability contribution. Although sawn aspen lumber is of no use in construction, the wood fiber itself is. Down to the smallest stems, it can be chipped and wafered mechanically. The trees regenerate from their roots, meaning they don't have to be replanted.

The chips, inches long by fractions thick, are flash dried, mixed with adhesives and hot-pressed into sheets, boards and strips. Result? A timber product of high and consistent quality, dimension and manufacturing tolerance; less thermal and humidity movement (swelling or shrinkage); surfaces able to be textured, coated and pre-primed for paint finishes; no knotholes, and it can be made as strong as plywood or particleboard.

It sounds almost too good to be true. Unfortunately, for all its woody, availability and environmental virtues, aspen falls prey to fungal infestation more than most woods.

With this hidden characteristic, untreated OSB components can succumb rapidly and badly to rot. The bonded wood chips absorb water and when wet, the panels can become an ideal home to fungal colonies.

What was needed to exploit the aspen's sustainability asset was a fungal deterrent that kept its potency over many years, and could be considered environmentally-friendly, economical, non volatile, and also completely compatible with the manufacturing process. This just happens to be a very good description of borates and their well-known biostatic properties.

During OSB manufacture, Borogard ZB's slow-release zinc borate is sprinkled into the shavings and adhesive mix before the hot-pressing stage. About 40 grammes per square meter are used, but this relatively small amount provides fungal protection in all climatic conditions.

If the wood stays dry, Borogard ZB's tiny crystals stay dormant. But if OSB gets damp, the zinc borate dissolves into action against fungus. It is actually mobile in damp wood.

With borate treated OSB there is fungus-free peace of mind for the home owner.

How borates stop the rot

Borates have long been known to be effective wood preservatives capable of controlling both fungal and insect pests in timber, and their efficacy has been established through research carried out by scientists around the world.

Borates are not directly lethal to an organism but rather are considered to be biostatic, and control degradation by inhibiting necessary oxidative metabolic activity at the cellular level - a constant energy-producing process necessary for life. Because the way it works is fundamental, borates are effective against a broad spectrum of pests, with no known development of resistance.