Although there are more than 70 species in this genus grouping of Dipterocarpus that grow in the Indo-Malaysian region, the lumber they produce is all marketed together as keruing. In the Philippines, lumber in this grouping is marketed as apitong.
Properties can vary widely from species to species within the grouping, so make sure that any purchase requests stipulate the density, color or other important properties, in order to avoid undesired characteristics.The trees within this genus can commonly reach heights of 200 feet with trunk diameters of 6 feet. An abundance of FAS lumber is therefore produced.
One characteristic to be aware of is the rare occurrence of silica within the wood, causing rapid blunting of tools. Silica dust can also cause allergic reactions in some people. Potentially troublesome is the presence of resin ducts. Exudation of resin in finished products, even if finished, can be troublesome. The resin, unlike softwood resin, cannot be "set" in the kiln-drying process and can build up on tools and sandpaper, causing machining or sanding difficulties.
Processing suggestions and characteristics
Density. The basic lumber weight, when dried to 6 percent MC, ranges from 35 to 45 pounds per cubic foot, or roughly 3 to 4 pounds per board foot. This is equal to about 20 percent heavier than red oak.
Drying and stability. This wood dries slowly, often with considerable degrade due to checking and warp. Generally, the wood is dried similarly to American oak. Sometimes, collapse occurs while drying, and this must be recovered by steaming, or else excessive localized swelling can occur in use.
Shrinkage from green to 6 percent MC ranges widely from species to species. Tangential shrinkage (the width in flatsawn lumber) can exceed 14 percent; radial, 7 percent.
Movement in service, which varies from species to species, is rather large, especially when compared to native U.S. species. A 1 percent size change tangentially can occur with 2 percent MC change; radially, with a 4 percent MC change. Correct final MC is essential to avoid size changes in-use.
Gluing and machining. Generally, apitong and keruing machine moderately well, similar to oak.
Gluing is moderately difficult, as with most denser species. The resin may also interfere with gluing. Typically, when gluing, the wood is glued within minutes after machining the mating surfaces to avoid resin exudation.
Strength. Due to its moderately high density, apitong and keruing's strength and stiffness are high. For dry wood, the ultimate strength (MOR) is 19,900 psi, stiffness (MOE) is 2.07 million psi and hardness is 1,270 pounds, with moderate variation from species to species. Comparative oak values are 14,300 psi, 1.82 million psi and 1,290 pounds. The high hardness makes it a good choice for flooring, especially industrial flooring, and other high-impact, high-strength areas. Moderate natural decay resistance (with some variation from species to species) makes this a good choice for boardwalks and exterior flooring.
Nails and screws have excellent holding power.
Color and grain. Heartwood varies from light to dark red brown or brown to dark brown, sometimes with a purple tint. The surface texture is moderately coarse with many small open pores. Surfaces would not be considered exceptionally smooth. The grain is usually quite straight.
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