Basic Principles of Building with Bamboo
Bamboo is arguably the most valuable, versatile, useful plant in the world. It is probably one of the oldest construction materials in history, used to make buildings, fences, utensils, toys, tools, boats, weapons, and musical instruments. In carbonized form, it was one of Edison’s most successful early filaments in his electric light bulb, and in its culm stage, when it first emerges from the ground, it is edible. Scholars have catalogued more than a thousand applications for this botanical cousin to corn, rice, and Kentucky Bluegrass(1), which grows on every continent on Earth, from sea-level in the Tropics to over 13,000-feet in the mountains.
With over a thousand species of bamboo, it ranges from the size of field grass to 120-foot stalks whose girth is about twelve inches. It grows with hollow chambers, each cordoned off with internodes. These internodes give the stalks strength, and, predictably, occur more frequently nearer to the base. One story on the naming of the plant is that the sounds given off when the chambered stalks burned – Bam! Boom! – had the obvious results. Perhaps its most amazing attribute, however, is the fact that each stalk, or culm, reaches its full height in six to eight weeks – literally, one can watch it grow!
In studies done at the Institute for Lightweight Structures (IL) at the University of Stuttgart in Germany, it has proven to be stronger per weight than steel. Because of this, it has even been used as reinforcing in pre-stressed concrete. Adding the fact that it is a extremely elastic, easily grown, beautiful, and has, thanks to its waxy coating, good resistance to weathering, this cheap, lightweight material seems to be a natural for use in our State’s Landscape Design and Construction industry.
A good way to think about how bamboo grows is to liken it to the grasses, with each spreading through underground rhizomes. Bamboo is divided into two main categories according to how it spreads; either clumping, which has a circular, ring-like growth pattern, or running, which sends rhizomes out in a radial pattern. The running bamboo has a bad reputation for ‘getting out of hand,’ one reason that the clumping varieties are becoming more popular. The spreading varieties can be easily controlled, however, by either surrounding the grove with metal, plastic, or concrete barriers two feet in the ground, by kicking the culms over in the Spring when they emerge, or, best of all, by harvesting the culms and eating them.
Each clump of bamboo, no matter how far reaching, is one plant. Many species of bamboo flower on long cycles of 30, 60, or even up to 120 years. Extremely interesting is the fact every plant of each species flowers at the same time worldwide. After flowering, the plants die, and it then takes between ten to fifteen years for the grove to regain its former vitality, sprouting either from the few surviving rhizomes or, more prevalent, from the germination and growth of the seeds.
Given bamboo’s widespread distribution and long history, there are many mistaken notions surrounding its growth and management. When starting a bamboo grove, do not be impatient to begin harvesting. It takes a plant between ten and fifteen years to achieve a large enough biomass to be able to support the extremely rapid growth of the large diameter canes. Another misunderstanding is that bamboo is a bog plant. Because of its rapid growth rate, bamboo does require a great deal of water, achieving larger girths in years when there are good Spring rains, but it does not tolerate standing-water on its roots. Perhaps the most often misunderstood aspect of growing bamboo is the frequency in which it can be harvested. Once the grove has attained the biomass necessary to support its rapid growth, too large or too frequent a harvesting of the larger canes will deplete the grove and sometimes lead to its demise. The best method is to only harvest the five-year-old canes. If a larger harvest is necessary, a longer period of revitalization will be necessary.
The type of bamboo that you might use for any building project will often be limited to what you can find growing around you. It is useful, however, to find or plant several different varieties, because they can have very different characteristics. When used for building, the most sought-after characteristic is the thickness of the walls, with the thicker walls having more strength and durability. If you are bending bamboo to achieve curved forms, the longer internodes seem to be preferable. Even if you cannot determine the identity of bamboo available, if you cut a piece and see that it has a thick wall, typically 1/4” and greater, this will likely work for most forms of simple construction.
If you are looking for large diameter canes with strong walls, the temperate varieties that do quite well in this area are Phyllostachys hetercycla pubescens, Moso Bamboo, Phyllostachys nigra ‘Henon’, Grey Henon Bamboo, and Phyllostachys bambusoides var, ‘Giant Japanese Timber,’ Madake Bamboo. These are all ‘timber’ bamboos that can achieve a girth of up to four inches in this region of the country. The Grey Henon, growing close to 70’ in the Southern Pines area, has a green-grey cast to it because of its heavy waxy coating. The Moso is a yellow in color, and supposedly has thicker walls, while the Madake is known for having a smaller diameter cane nearer the base, which expands to the desired (3” – 4”) at three to four feet above the ground. Phyllostachys vivex is another large diameter species that is reputed to have walls that are too thin; in many cases, however, the walls are sufficiently thick to make this species very useful.
If you are looking for smaller diameter canes, useful in doing more detailed work, the Phyllostachys aurea, Golden Bamboo, is very strong walled, with the unusually feature of having very compact, distorted internodes near the base. Another smaller diameter variety, Sinobambusa tootsik, Tootsik Bamboo, has strong, thick walls, with longer than usual internodes, useful in achieving cured forms. This last is the most popular variety used in the making of flutes. A very beautiful as well as strong variety, Phyllostachys nigra ‘Hale,’ Hale of Black Bamboo, has a dark, maroon-black coloration that makes a striking look either as an ornamental plant or when used in construction. Another ornamental variety that is also useful is the Phyllostachys viridis ‘Robert Young,’ Robert Young or Green Striped Bamboo, which, in addition to having medium to large diameter canes, is widely used for making paper.
Harvesting and Curing:
When cutting bamboo for construction purposes, it is best to use canes that are three to five years old. These older canes have slightly thicker and much tougher walls, whereas the younger canes are made up primarily of water and will readily split when dried. The best way to determine the age of the cane is by the coloration. First-year canes are dark, shiny green and very clean. Second-year canes are still somewhat dark green, but are neither as shiny nor as clean (birds love bamboo groves). Older canes tend to have much more yellow in them, and actually feel stiffer when you shake the stalk. Other signs that a cane is ready to be cut are when the first node above the ground has aerial roots present and when the culm sheath (near the ground) is old and brittle. Some experts can tell the age of a stalk by counting the leaf rings of the side branches, while in Oriental cultures, the growers often keep track of the age by scratching the dates in the base of each years’ new canes.
Cutting and curing bamboo go hand in hand, and there are many, often conflicting theories about how to best go about these tasks. All agree that it is advisable to cut each stalk as close to the ground as possible, to avoid the shin-barking and toe-stubbing punji stakes from wreaking revenge on later harvesting trips. A good quality, pull-stroke, hand pruning saw seems to be the best tool for toppling the stalks. Once down, the debate on how to handle the canes begins. Generally speaking, it is best to leave the fallen canes in the field for up to a week, with the leaves still on. This will help to pull the starches, which attract the various insects, out of the cells as the leaves continue to work. After this time period the stalks are collected and trimmed. It is important to do a very careful job when trimming the side branches, for if sharp-pointed spindles are left, again they will take their revenge during the further working of the canes.
The canes are then bundled together and submerged in water (running water seems best) for between two weeks and two months. This operation is an effort to further remove the starches from the cells. After removal from the water, the canes need to be washed. Bird guano and other debris that attaches to the canes will provide fertile ground for fungus and bacterial activity. These can diminish the durability of the stalk, as well as detract from the beauty of the canes. In the Orient, this operation is often accomplished on riverbanks by grasping handfuls of sand in a cloth and rubbing the entire cane clean. Simple detergent in water and a coarse cloth seem to work well; even rubbing the cane with the second finest grade of steel wool (the finest will disintegrate too easily) will work. Try to avoid damaging the outer waxy coating, because not only will this leave striations that may detract from the overall look, but it will also create an opening for pests to access the cellulose wall. Similar to any wood product, it is recommended that the canes then be stacked in a cool, dry place to cure for three months to a year.
When properly cured, bamboo will last, if in contact with the ground, for two to three years; if exposed to the elements but not touching the ground, for five to ten years; and if protected from the elements and not touching the ground, indefinitely.
Cutting to Length: A key in preparing bamboo for construction of any sort is in how it is cut. It is best to cut each length so that both ends are trimmed as close to the outside of an internode as possible, leaving each chamber intact. If the canes are cut between the internodes, the exposed ends offer easier access for insects and disease; the internodes, because of their denser cell structure, seem to resist invasion better. Getting similar diameter canes of equal length can be a time intensive task, but it is possible because the varying lengths of the internodes nearer to the base of the stalks allow you to adjust where you make your cuts. If you have no alternative but to cut one end of a stalk between internodes, it often works better to arrange that end at the bottom of the structure.
Splitting: Splitting bamboo with hand-held knives is a very tricky operation. Unless well trained in this task, splits will wander with the grain to the outer walls as often as not. At the Georgia Coastal Gardens and Bamboo Farm outside of Savannah, a simple splitter has been devised. An old cleaving knife was centered and welded on the interior of a three-inch angle iron, close to one end with the cutting edge facing the long dimension. The 12-ft long apparatus is supported on sawhorses. Each cane is simply centered and hand-pushed past the blade, splitting the stalks cleanly.
Sometimes, bamboo ‘splits,’ or thin, flat segments of the cane, are desired. These can be achieved by splitting the lengths of cane with circular, hand-held devices that have centrally mounted blades. These are usually designed to divide each cane into either four or six pieces. The remnants of the internodes can then be trimmed off, leaving flat, flexible lengths of highly useful ‘splits.’
Bending: Bamboo is very flexible and can be bent, almost to any shape desired, whether it is split or whole. Because whole canes are stronger by virtue of their shape, in larger construction projects they may be more desirable. When the canes are freshly cut, or immediately after removal from their water immersion, they can be trained to bend by gradually forming them to the desired bend. Sometimes, for special projects, forms are built and the bamboo is attached to these to remain during the drying process. When slight curves are desired, especially when using larger diameter canes, weights are tied to the poles, and over time, with the poles leaving against wall or suspended between two supports, the proper curve evolves.
“Bamboo, the Giant Grass,” National Geographic, Vol. 158, No. 4, October,
1980. Washington, D.C.
This is one of the best overviews of bamboo published, and was used as the basis for the Introduction of this article.
Bambus-Bamboo: Bamboo as a Building Material, edited by Klaus
Dunkleberg of the Institute for Lightweight Structures at the University of Stuttgart, Germany, pub. by Karl Kramer Verlag, Stuttgart, Germany 1985.
This is by far the best publication available on the structural qualities and construction details for building with bamboo. Also, Kramer has, as one of its specialties, the publishing of books and articles on both growing and building with bamboo.
Linton, Frank, Conversations with, Spring 1995.
Mr. Linton is an Agriculture Research Assistant III, working for the College of Agriculture and Environmental Sciences, Cooperative Extension Service, at The Coastal Gardens at the Coastal Gardens and Bamboo Farm, #2 Canebrake Road, Savannah, GA 31419. Although he claims not to be an expert, his careful observations over many years makes him a very valuable resource.
The Bamboo Fences of Japan, Suzuki, Osamn and Yoshikawa, Isao;
Graphic-sha Pub. Co., Ltd., 1-9-12 Kudan-Kita Chiyoda-Ku, Tokyo, 102, Japan.
This is one of the best books available with good color photos of a wide variety of different fencing details. It can be obtained in this country by contacting Dave Flannigan, “The Bamboo Fencer,” 31 Germania, Jamaica Plain, MA 02130.