What you need to know about bamboo
August 30, 2018 | 3:50 pm CDT
Bamboo is not wood, but a grass with no woody material in its stem. But we are seeing more and more use of this grass in cabinets and as a substitute or adjunct to "good old, solid wood." And I have seen some pretty good- looking bamboo items.
This grass that looks just like the bamboo fishing rods used by Huckleberry Finn and Tom Sawyer, only larger, is being harvested in a manner similar to trees. The round, hollow stem, with closed sections every foot or two, is sawn lengthwise into long narrow strips that are then made into rectangular-cross-section pieces that take out the curvature.
The strips are then edged glued together into veneer and glued into "plywood" panels that look similar to and behave much like wood. There is a growing list of active importers who bring bamboo products into North America.
There are more than 1,000 species of bamboo. The properties and appearance of the various bamboos varies greatly. This is where confusion lies as people tried one supplier's material and liked it, but found a second supplier had a different product that did not work as well.
In short, not all bamboo is the same and, like wood, has many variations in appearance and properties from species to species. My advice is to know your supplier well.
The bamboo tree itself is very fast growing and, as such, promises to supply fiber needs in many parts of the world, especially tropical areas, where wood-based timber growing takes too long. A bamboo tree can reach 40 feet and over 6 inches in diameter within 4 years and can in a few more years, when growing conditions are good, reach a height of 90 feet and a diameter of nearly 2 feet (but it is still a hollow stem).
When harvested, the root system will send up sprouts which perpetuate the species with little human intervention. Some "wild" grass forests still persist today, although most stems are fairly small in diameter. In many parts of the world, bamboo is grown in managed plantations.
Properties of bamboo
The properties of the different bamboo species can vary greatly. For example, Calcutta bamboo has a stability when the humidity changes that is close to oak, but some bamboo varieties shrink and swell twice as much. Not all commercial bamboo lumber or plywood will have the desired properties and characteristics you need.
Make sure you talk to others who are using the same bamboo species from the same supplier that you will be using before you begin investing. Further, make sure that your supplier will not be changing species without your knowledge. Because of the potential for large movement of bamboo, you will have to pay particular attention to obtaining and maintaining the correct MC.
The piece of bamboo in the picture consists of long, narrow strips (about 1/8 inch in thickness and 1/4 inch wide) that are edge-glued together to form the 1/8 inch surface veneer.
A true picture
Most people believe that bamboo is very bendable and lightweight. However, bamboo products like the one pictured are actually as heavy (40 pounds per cubic foot) and as strong in bending as oak. The material is easy to cut and fasten with metal fasteners or adhesives. (I prefer a good PUR adhesive.)
As consumers begin to ask more and more for bamboo, we will have to learn to work with this grass, even though most of us have sawdust in our veins. Careful purchasing, handling and moisture monitoring assure us that we will not have any major problems adding bamboo to our repertoire.
Processing suggestions and characteristics
For the purposes of this article, the properties listed are for Calcutta bamboo (Dendrocalamus strictus), which is the most common bamboo in the Indian forest, making it a very important species in India and other Asian tropical countries.
The density of bamboo is about 40 pounds per cubic foot, which is similar to oak. As the bamboo panels will be 100 percent bamboo, they will be slightly heavier than an oak plywood panel of similar thickness, as most oak plywood uses a lower density species for the interior plies.
Bamboo will always be dried at the site of manufacturing. Drying is not difficult. Shrinkage in drying is similar to oak, but there is little difference between radial and tangential shrinkage.
Gluing and Machining
Calcutta bamboo (and many other bamboos) do glue well when making a laminated product. The high density does mean that surfaces must be well prepared. It may take some experimentation to determine the best glue spread rates. My personal feeling is that a PUR adhesive is an excellent choice for the furniture and cabinet shops when gluing pieces of bamboo.
Machining of bamboo is reported to be very good, but again there will be variation when the species change. I could not find any allergic reactions from contact with the bamboo dust in the literature.
The relationship between relative humidity and moisture content for Calcutta bamboo is nearly identical to the standard tables used for wood in North America. Further, the shrinkage is similar to oak, with a 3 percent MC change resulting in a 1 percent size change. However, shrinkage and swelling are essentially the same in the radial and tangential directions (across the grain directions). Therefore, end checking is a risk, but is moderated by using cross-laminated plywood construction. In short, bamboo must be handled carefully when it comes to storage humidities and moisture issues, just like oak and other fine woods. As most bamboo will come from a humid, tropical location, some drying in our North American environments can be expected. It would be prudent to expose the bamboo to the drier environment, especially in the wintertime, to avoid shrinkage in a finished product.
Lengthwise (longitudinally), this bamboo species does not shrink or swell appreciably, just like wood.
(Caution: Some bamboo products being sold are very unstable with MC changes...know the material you are working with.)
The strength (MOR) ranges from 12,000 to 22,000 psi, which is a bit higher than red oak The stiffness is 1.1 to 2.9 million psi, which is again a bit higher than oak.
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