Bamboo

Common Name(s): Bamboo Scientific Name: Hundreds of species among dozens of genera from the Poaceae (grass) family (Many timber-producing bamboos are from the Phyllostachys and Bambusa genera) Distribution: Most timber-producing bamboos are from south Asia Tree Size: Some of the largest bamboos can be up to 50-100 ft (15-30 m) tall, with a 3-6 in (10-20 cm) diameter Average Dried Weight: 31 lbs/ft3 (500 kg/m3) to 53 lbs/ft3 (850 kg/m3) Specific Gravity (Basic, 12% MC): .38 to .64, .50 to .85 Janka Hardness: 1,410 lbf (6,270 N) to 1,610 lbf (7,170 N) Modulus of Rupture: 11,020 lbf/in2 (76.0 MPa) to 24,450 lbf/in2 (168.6 MPa) Elastic Modulus: 2,610,000 lbf/in2 (18.00 GPa) to 2,900,000 lbf/in2 (20.00 GPa) Crushing Strength: 8,990 lbf/in2 (62.0 MPa) to 13,490 lbf/in2 (93.0 MPa) Shrinkage:Diameter: 10-16%, Wall Thickness: 15-17%

Color/Appearance: Generally a uniform and pale yellow to almost white. Live bamboo that has been left standing too long frequently develops fungal decay, discoloring the wood with brown or black streaks and patches.

Grain/Texture: Being a monocot in the grass family, bamboo does not have any sapwood/heartwood or growth rings. Texture is very uniform, and ranges from medium to fine depending on density. Bamboo that has been split and processed into lumber will have intermittent variations in the fiber at each node on the stem.

Endgrain: Resembles the endgrain of palm—another monocot. No data is available to distinguish between bamboo species, but bamboo can usually be distinguished from wood and palms by the hollow stem, pale color, and the lack of rays or visible pores.

Rot Resistance: Bamboo used in exterior conditions is perishable, and will deteriorate in a matter of years. This is also paralleled in the short natural life cycle of bamboo, where many species quickly reach full maturity after only two or three years, and are subsequently attacked by decay mold and fungi, typically collapsing only a few years later. Bamboo is also susceptible to insect attacks such as powder-post beetles, termites, and marine-borers.

Workability: By woodworking standards, bamboo can be different. It is not necessarily difficult to work with, but depending on the species, it may require some special care. Bamboo fibers tend to split and pull out when being cross-cut, (applying masking tape across the cut line beforehand is recommended to prevent this sort of tearout). Also, bamboo is very high in silica—from .5% to 4.0%, found almost entirely in the outermost layers of the stem—so care must be taken when processing lumber. Carbide cutters are strongly recommended, and surface sanding is suggested instead of thickness planing with steel cutters, both for longevity of cutting edges, and quality of the finished surface. Bamboo glues, stains, and finishes well. When turning giant bamboo species, tools dull quickly, and endgrain tearout is common, but tearout tends to be very shallow, and the endgrain sands nearly as easily as the facegrain, and an overall smooth finish can be achieved with minimal effort.

Odor: Bamboo has a unique, earthy smell while being worked.

Allergies/Toxicity: Although severe reactions are quite uncommon, bamboo has been reported to cause skin irritation. It’s unclear whether the bamboo itself actually causes the irritation, or if it is simply due to the decay fungi commonly present in the material. See the articles Wood Allergies and Toxicity and Wood Dust Safety for more information.

Pricing/Availability: Bamboo is typically available in three forms: in hollow turning-blank sizes from giant bamboo species; in glued-up boards (flooring) and sheets made from many smaller strips; and in paper-backed veneer. Although bamboo is a very abundant natural resource, and prices for raw material tend to be low, (it is often called the “poor-man’s timber” throughout bamboo’s natural range), prices can be much higher for the energy-intensive, processed and glued-up imported products: often exceeding the cost of domestic hardwoods.

Sustainability: This wood species is not listed in the CITES Appendices or on the IUCN Red List of Threatened Species.

Common Uses: Veneer, paper, flooring, fishing rods, ladders, scaffolding, musical instruments (flutes/woodwinds/chimes), furniture, window blinds, carving, turned items, and small novelty items.

Comments: Bamboo is one of the most unique plants on earth. Unlike trees, bamboo grows initially at full width, with no tapering or horizontal growth. Some species can grow up to three feet a day! After just one year, bamboo reaches its full height, and in subsequent years, the stem (called the “culm”) continues to harden. The strength of the bamboo continues to increase for the next two to four years; most species of bamboo are considered fully mature in just two to three years. After this time, fungus and mold begin to cover the outside of the culm, eventually working its way into the interior, weakening the plant over several years before it eventually collapses from decay. For this reason, there is a window of time when it is considered best to harvest bamboo for optimum strength and hardness.

Bamboo is known to have a high shrinkage rate when initially being dried, amounting  to 10-16% in culm diameter and 15-17% in overall wall thickness. Bamboo tends to shrink more towards the outer wall than at the interior: for this reason, surface checks can develop on the outside of the culm if it is dried too rapidly. However, despite the high shrinkage rates for bamboo, once it has adjusted to equilibrium moisture content, it is somewhat stable in use.

Although many prefer the aesthetics of bamboo for its unique, down-to-earth, Asian-flair, the real story on bamboo lies in its mechanical properties. Although it is hard to typify a group of over one thousand different species into a single set of mechanical values, on the whole, bamboo possess some of the best stiffness/strength characteristics, and strength-to-weight ratios of any woody material on the planet.

But the difficulty in qualifying bamboo’s strength lies not only in the abundance of species, but also in the lack of standardized testing: a complicating factor is that bamboo itself tends to be harder and stronger toward the outside of the culm, gradually getting softer and weaker toward the center. In some testing, certain species of bamboo at certain areas of the culm have exhibited stiffness (m.o.e.) and bending (m.o.r.) values far exceeding that of any hardwood. The only “weakness” of bamboo is simply inconsistency: with so many different species, and so many ways to cut and process bamboo, it is hard to be assured of the mechanical characteristics of any given bamboo product.

Related Species:

None available.

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Scans/Pictures: As you can see from the pictures, there are two styles of bamboo commonly used for flooring, which would loosely correspond to flatsawn or quartersawn sections in woodworking terminology. Each type is formed by gluing smaller bamboo strips either in a horizontal or vertical orientation. The giant bamboo blanks and turned vase below are Dendrocalamus asper.