Oriented strand board.
Oriented strand board, or OSB, or waferboard, or Sterling board (UK) or SmartPly (UK & Ireland) is an engineered wood product formed by layering strands (flakes) of wood in specific orientations. In appearance it may have a rough and variegated surface with the individual strips (around 2.5 by 15 cm (approx. 1 in by 6 in) each) lying unevenly across each other.
It is manufactured in wide mats from cross-oriented layers of thin, rectangular wooden strips compressed and bonded together with wax and resin adhesives (95% wood, 5% wax and resin). The layers are created by shredding the wood into strips, which are sifted and then oriented on a belt or wire cauls. The mat is made in a forming line, the layers are built up with the external layers aligned in the panel's strength axis with internal layers cross-oriented. The number of layers placed is determined partly by the thickness of the panel but is limited by the equipment installed at the manufacturing site. However individual layers can also vary in thickness to give different finished panel thicknesses. The mat is placed in a thermal press to compress the flakes and bond them by heat activation and curing of the resin that has been coated on the flakes. Individual panels are then cut from the mats into finished sizes. Most of the world's OSB is made in the USA and Canada in large production facilities. The largest production facilities can make over a billion square feet of OSB per year.
Different qualities in terms of thickness, panel size, strength, and rigidity can be imparted to the OSB by changes in the manufacturing process. OSB panels have no internal gaps or voids, and are water-resistant, although they do require additional membranes to achieve impermeability to water and are not recommended for exterior use. The finished product has similar properties to plywood, but is uniform and cheaper. It has replaced plywood in many environments, especially the North American structural panel market. The most common uses are as sheathing in walls, floors, and roofs.
While OSB does not have a continuous grain like a natural wood, it does have a specific axis of strength. This can be seen by observing the alignment of the surface wood chips. The most accurate method for determining the axis of strength is to examine the ink stamps placed on the wood by the manufacturer.
All wood-based structural use panels can be cut and installed with the same ease and types of equipment used with solid wood. In 2001, 19.4 million m³ of OSB panel was produced in the US. The US is Canada's largest OSB market, receiving 98% of its export product in 2005.
Some manufacturers may treat the wood chips with various borate compounds which are toxic to termites, wood boring beetles, molds, and fungus but not mammals in applied doses. Buyers are recommended to seek borate modified wood products for construction, particularly in warm moist climates.