The following report was revised in February of 2004 by our Chairman, Leimana Pelton,
and local architect, Valerie Simpson. It is an excellent synopsis of identifying local species,
and the management and treatment of bamboo in Hawaii.
It is reproduced here for you convenience and edification.
This report was originally made possible by a grant from Hawaii County Department of Research and Development to Save Hawaii,
a non-profit environmental organization, with the intent to examine the feasibility of locally grown bamboo as an acceptable
construction material for Hawaii.
Our County Department of Research and Development recognizes the need for sustainable and
reliable locally grown building materials and the local agricultural possibilities of bamboo. They therefore sponsored this
report as a resource for the people of Hawaii. Eco Terrestrial Concepts, a team of individuals committed to sharing information
about bamboo gathered through travels, seminars, interactions with leading bamboo authorities, and from explorations
and experiments of their own, has provided the research and the final report.
This report is based on three premises: 1) That there is a need for a locally grown and processed building material that could
help reduce Hawaii’s dependency on depleting materials from the continental United States. 2) That bamboo could help fill a
need to reuse former sugar cane lands, especially in “marginal” areas where bamboo tends to thrive, which would result in 3)
providing expanded opportunities for local farmers.
Bamboo has a reputation around the world as a strong and versatile construction material. There are countless extraordinary
examples of bridges, all types of buildings, as well as the most remarkable scaffolding for high-rise buildings.
In our efforts to gather information from both traditional and current technologies, we have sought out the foremost
authorities and knowledgeable professionals in various fields relating to bamboo construction, without whose inspiration
and support this report would not have been possible.
Architect Simon Velez of Colombia provided our initial inspiration for building with bamboo with his outstanding examples
of ingenuity, and has graciously allowed us to penetrate his world of innovative bamboo construction from the groundwork
to the finish details at many project sites throughout his native country in South America.
Engineer Jules Janssen, of the Netherlands, made important recommendations during his series of seminars in Hawaii. First,
we must plant as many of the best timber species as possible. Then, we must test them to determine the highest quality
variety for our particular climates, where they will grow to full potential in size and strength. Next, he advised us to
build a treatment facility in order to have reliable results for our efforts. Finally, he suggested that we use our bamboo
locally for building and to make value-added products for export.
Bamboo researcher Dr. Walter Liese, Ph. D. of Germany and Engineer Victor Cusak of Australia also honored us with extensive
information from their lifelong research in their lectures during their stay here. Dr. Liese provided the adaptation of the
standard “Boucherie” method of wood treatment into a model custom made for bamboo. Victor Cusak owns one of the largest
selections of bamboo species in the world.
We begin our report with an examination of current local bamboo species, comparing the characteristics of the four species
of clumping bamboos ( Bambusa beecheyana, Bambusa vulgaris,Guadua angustifolia and Hirose) that we have identified, harvested,
treated and used in experiments as a building material. In addition there are a few other species that are discussed as being
potentially useful but have not yet been tested. Then, we discuss the management of bamboo clumps in order to maximize quality
and minimize effort from propagation to harvest, with a special section on managing older, wild clumps. In the next section,
we describe various treatments methods, including the construction of our own pressurized sap displacement facility.
And a discussion of curing methods concludes this report.
IDENTIFYING LOCAL BAMBOO SPECIES
There are many species of bamboo on the Big Island. They can first be divided into two main groups as either “running” bamboo; which in Hawaii has given bamboo in general a bad name because of its invasive nature, and “clumping” bamboo which remains in a relatively small area, readily mixing with other plants. In temperate climates, running bamboo may be the best, and perhaps only, option for construction material. We encourage people to explore the utilizing existing running bamboos, while being careful no to spread them. All bamboos have utilizable characteristics. In tropical climates, most of the clumping varieties are considered to be better for building material, with noteable exceptions, especially the attractive and most commonly seen yellow Bambusa vulgaris vittata or “Green Stripe.”
Many clumping varieties can be found around the island. Some of the finest examples are found in watershed areas where bamboo thrives and contributes to soil and water retention. Because bamboo is highly adaptable to its environment, its characteristics may change dramatically in different locations.
It is hypothesized that at least two of the established bamboos of the Big Island have mutated over time from their imported origins Hirose and “Parker giant”. Mutation can occur when the plant flowers and produces viable seeds. Each seed can produce a significant variation. Flowering is rare and varies from species to species; behavior differs even among the same species in the same location. There are two general categories of flowering; gregarious, and sporadic.
When a clump “gregariously flowers”, every culm will flower resulting in the death of the clump. A gregariously flowering bamboo's lifecycle varies tremendously. There is no mention of any species cycling sooner than 20 years, and some species haven't flowered in over one thousand years. Because of the extremes and lack of attention to this part of bamboo history there is little documentation older than 40 years. Every seed produces new evolutionary possibilities and the new plants that result often require a different identification for their next cycle of growth, and receive new names.
Subsequently some of the clumping species found in Hawaii are difficult to identify. Two examples are varieties we call Hirose and “Parker Giant”. Another problem is that there are no local taxonomists for bamboo here in Hawaii. In fact, it is mostly due to Professor Norman Bezona (now retired) and recent student pressure that our local universities have even considered “bamboo studies” let alone hire a staff expert.
When a clump “sporadically flowers”, only a small amount of blossoms appear, and the clump does not suffer. Nonetheless, any successfully germinated seed could produce a mutant variety from the parent plant that would in turn have different characteristics and require a new variety name.
Following is a description of the bamboo species that are established on the Big Island. The first four species have characteristics according to our experience, research and observations, that render them as possible construction material.
Description by Species
Bambusa beecheyana: Has a mostly round diameter of up to 51/2” and a height of 25’-65’. It is dark green with tilted nodes, causing the culm to arch slightly in opposing directions after each node, and tends to lean away from the clump. In crowded conditions this species as well as any compact “clumper” will meander around in order to find it's way to the sunlight at the top of the clump. The walls are thick at the base (first ten feet). Node spacing is close at the base and normally increases toward the top. It thrives best in wetter climates and is distinguished by a white powder on the surface that is exposed after the sheath drops.
B.beecheyana is the most common variety of clumping timber bamboo on the Big Island. It has thick walls and good bending strength but exhibits quite different characteristics depending on its habitat. Because it is starchy, powder post beetles attack it. This species might be classified as a medium strength timber. One notable characteristic is the beautiful color variations in the “wood” when sanded and carved. When grown in very little soil, the clump height may reach only 15-30 feet, and a lot of orange discoloration appears on culms and leaves. It has been reported that all B.beecheyana has mosaic virus. That could contribute to the orange colors. We do not know of any B.beecheyana on the island that has been fertilized. It seems to do quite well in older clumps from its own mulch, even when competing with aggressive trees, as long as there is sufficient soil.
Bambusa vulgaris(Green): Also called “common bamboo,” its origin is unknown but believed to be an early Polynesian introduction. Culms have a 2”-4” diameter, are thick-walled at the base and grow 40’-60’ tall. Though reasonably strong, it is not very dense, therefore lightweight. It has a and high starch content so bore beetles love it.
Guadua angustifolia: In other parts of the world, reaches 6” in diameter and averages 66’ in height. It has thick walls and is dangerously thorny. The culms have short internodes with white bands above and below the nodes. Species are both variegated and green. While not a starchy bamboo, it is susceptible to beetle and fungus attack.
Recently introduced to Hawaii, Guadua is one of the world’s finest timber bamboos. It is loose clumping and, unlike any other clumping species, has a natural culm spacing of one to two feet in mature clumps due to long neck rhizomes, and therefore creates more of a bamboo forest effect environment. It easily coexists with tall forest trees but inhibits the growth of new seedlings due to its matted root system, which is common around tropical clumpers. This does help with controlling invasive plant species.
The clumps at the Bamboo Village Hawaii site at 900’ elevation are reaching 80 feet after only six years and are up to 6” in diameter. They could still increase their overall size. All the clumps of Guadua angustifolia we've seen here branch all the way to the ground.
There are other subspecies that have fewer thorns and or do not produce lower branches on the mature culms. It is important to remove all the branches and nodal thorns (which are about 4” long) as they begin to grow unless the intent is to create a very hazardous environment for both people and the tender new emerging shoots. Pruning is highly recommended to help to minimize damage to neighboring culms, farm workers and to facilitate harvesting. Telescopic pruning tools work very well for this. We have witnessed one clump here sporadically flowering.
Bambusa”Hirose”: Bamboo Hirose is a timber Bamboo, this bamboo has not yet been officially identified. It is a timber bamboo, which, we are told, was brought to Hawaii from India. When first planted in Hawaii it grew to 6” in diameter with thick walls. The original five plants all seeded and died, producing only one seed that germinated. From that seed, this current strain, now grows 2”-5” in diameter. Some of the culm sections are oval but most are round. The few clumps found growing here are very straight and reach 60'- 70' tall with thin, strong walls and long internodes. Hirose possesses a good strength-to-wall thickness ratio but cracks easily under heat stress or direct sunlight. It also cracks when tooled carelessly. According to the preservation tests done by entomologist and researcher, Mark Mankowski PHD, at the UH Manoa campus, it appears to be the most resistant to powder post beetle.
”Parker Giant”: This Bamboo has not yet been positively identified yetin Hawaii. It can reaching 10” diameter with up to 2” thick walls at the base, continuing with very thick walls, this is the largest known local timber bamboo. From an established clump in Kohala, it has been divided and sold to numerous growers throughout the Big Island. We expect this superior species to become available for building in perhaps 8 to 10 years. With plenty of water, drainage, and fertile soil, culms could reach 120’ in height. A clump of this magnificent species was donated to the Panaewa Zoo for everyone to watch as it grows.
Although we have not yet used this species structurally ourselves, , the Parker Giant planted at the Bamboo Village Hawaii (BVH) forest site is producing excellent growth. It seems that this species is slow to get started but with enough available nutrition can produce dramatic results.
Bambusa vulgaris vittata: (Yellow with green stripes): 2”-5” diameter, 30’- 60’ tall with medium wall thickness. Culms lean outward from clump rather than growing straight up. Its weak walls tend to crack and split and bore beetles will eat away all structural integrity. Though large, beautiful, and commonly found everywhere in Hawaii, we do not recommend its use for permanent construction.
Dendrocalamus apus: Peter and Susan at Quendembo Nursery state that this species is an excellent timber choice. In the fourth shooting season the BVH specimen, from Quendembo, doubled the number of culms in one year! They are now 3” diameter, and 50 ’ tall. Like all the Indonesian varieties the leaves are very large and look like hands spread out to receive the sunlight. The culm walls are very thick and appear to be strong. From the first pieces cut, to thin away the ”bush”, there was no noticeable beetle infestation even without treatment. Therefore, it appears that this variety has a good resistance to them. To our knowledge locally raised D.apus has not yet been tested or used structurally in Hawaii.
Dendrocalamus strictus: The first experience we had with Strictus was with poles imported from Vietnam. They were all treated for pests and straightened with fire. The poles were nearly solid, very strong, and somewhat pliable.There are many different cultivars here in Hawaii, possibly due to the wide spread occurrence of the species around the world. The straightest example, we have, comes from Kim Higby of Hale Ohe' Nursery in Hakalau. Having moved a large portion of this clump to the BVH site when it was approximately 3 years old, it has been there now another three shooting seasons and grows over 2” diameter and 35’ tall. The clump arches out nicely from the top half. It branches perpendicular from the culms starting at the ground, which necessitates trimming if the clump is to be ” managed” for harvesting purposes or appearance; in either case its a good idea, otherwise it becomes interlocked making removal of any culm not at the perimeter of the clump, practically impossible.
Another Strictus cultivar at the BVH site has much smaller leaves and arches away from the clump beginning at the ground. It is a short plant of approximately 10’ tall after 2 shooting seasons, with a diameter of 1”. The most unusual cultivar of Strictus seen at two locations has culms that actually grow in loops and other bizarre configurations. Other characteristics are similar to the above.
There are many other attractive bamboo species planted on the Big Island that show potential as timber but will not be included here due to a lack of information during the short time that they have been here.
Starting a Clump from a Young Plant or Rhizome
This report is not intended for monocropping farmers and therefore recommendations here are directed to sustainable interplanting with other compatible plant species. Caution must be used with regard for how falling culms may impact neighboring plants and structures, not to mention utility wires.
The object of management is to create healthy and accessible stands of bamboo. As the clump matures, accessibility of desirable culms is accomplished by opening a path into the center and creating a ring of culms around an open center so that most of the culms are easily accessed from either the inside of the ring or the outer circumference. Because the clump will naturally attempt to fill in the gaps if given the time, pruning must be consistently maintained. It won't hurt the plant. Think gardening (food source) or lawn. More sap energy will go to the remaining culms, and the trimmings can become mulch.
Let's start at the beginning. You have chosen wisely the right potted bamboo, or maybe you were fortunate to get a rhizome division, for your unique environment. Because you want the best for the new arrival you prepare an oversized hole mixing the loose soil with lots of good stuff like compost, manure, cinder (to aerate) and any other ingredients you care to add. Complete the mixture with a plentiful layer of mulch and soak with water. Of course, please realize that bamboo should not be planted in a location where water does not drain quickly. It will rot the roots.
During their first year the plant will produce a 'bushy juvenile' with leaves to the ground. (The juvenile plants proportions often reflect that of the species at maturity.) As the plant progresses the ”bush” supplies the energy to push up the new culm shoots higher above the bush during the following shooting seasons.
A bamboo clump might be compared to a family, wherein the parents supply the children with food. Often the "parents" will produce more shoots than they have sufficient nutrition to support, so don't be disappointed to see shoots die or a culm start to grow and then the top dies. This is an indicator to use in determining fertilizer strength and quantity. Dieback might also be due to lack of water or root damage.
Once the tops of some of the culms have developed into fully formed, leafy branches you may begin pruning the bush away. Eventually this will produce a lower area comprised of culms at various stages of maturity, including the new shoots. It is important to note that one must be careful not to remove the leaf source of food before the new culms are foliated, otherwise their food production supply will be cut off!
It is a good idea to supply fertilizers on regular intervals, for instance, by the month or moon cycle. They will be stored up and used by the bamboo in the growth cycle.
Each new shoot could be tagged, or marked with the year (month optional) it emerged so that you can determine when that culm will be ready for harvest.
By the end of the growth period, expect the color of the older parts of the clump to fade. This indicates sap starch (food) depletion. The photosynthesis activity of the leaves stimulates this production of food. If the new shoots are able to develop their leaves before the parents are completely depleted, then their leaves will join in the process. However, those same new culms may simply stop growing before the branches and leaves develop, allowing time for enough support before continuing to grow. The leaves will also fall without water, leaving the clump looking dead, only to regrow at the beginning of water reintroduction. This can take months because it occurs, here in Hawaii, on the rainy side, during the slower growth period of winter. This also coincides with the appropriate time for harvesting the older mature culms; or in the case of immature clumps, removing the congested older bush culms.
For ease of harvest and to promote straight poles, the clump should be made to grow in small groups, with adequate space between. This occurs by cutting some of the new shoots before they reach 2 feet in height. The shoots of this size are edible, and particularly delicious if they are protected from the sun.
Harvesting culms should occur before dieback of leaves at the top occurs to prevent dangerous and unsightly dead culms that can break and fall from heights that pose a threat in high winds and harvesting procedures. This probably would not happen before the eighth year but depends on the size of the bamboo. Smaller varieties mature faster. Harvesting Culms aged a minimum of three to four years is suggested for any bamboo variety over 1.5 inches in diameter at maturity.
Generally speaking, with any bamboo, you can expect on the average, a 1” increase in culm diameter each year together with at least 10’ added to the height if the clump is healthy. The larger the overall size the longer it takes to reach maturity.
Spacing between starter plants depends on the relative size of the variety that you are planting. The anticipated height and diameter together with the outward leaning characteristic will determine the appropriate space surrounding the expected mature size of the clump, which will vary with the way it is managed.
When used as a windbreak you will want a dense "hedge wall" designed to be harvested from the sides. I would not suggest crowding a property boundary as you will need ongoing access to the outside to manage the row. To mitigate soil erosion from a steep slope you would probably want the clumps to be close enough so that the root systems from each clump will extend to the next. Clumping bamboo root systems consist of creature-like rhizomes that extend from the base of each culm. From these rhizomes vast amounts of smaller roots extent out in all directions forming a mat that interlocks with the other rhizomes in the clump. This matrix is shallow and holds the soil tightly preventing erosion. The lateral roots are easily identifiable; almost white and interlocking. Each clump is actually one plant that supplies it's own roots with an abundant layer of moisture holding nutritious mulch. Bamboo does however respond vigorously to added fertilizer, particularly when topped off with a deep mulch layer. Yum! Imagine the sweet juicy shoots and deep green new culms reaching for the Sun joyously! To see this miracle and feel a part of the process is a deeply enriching experience.
With good drainage, one to two feet of good soil will allow plenty of depth for clumping timber bamboos. Once again, they thrive on plenty of water and fertilizer. Abundant foliage indicates a healthy plant. The quality of the culm wood, speed of growth and final height depends on the bamboo’s growing conditions. Poor conditions result in weakened structural value, as well as degraded visual characteristics. Occasional stressing of plants during periods of the growth cycle has been known to result in greater strength and resilience. This would happen naturally during droughts, etc. unless you have them on drip systems.
Management of a wild clump
Many old stands of bamboo around the island have been used mostly for shoot harvesting, or cutting accessible poles easily without regard for the health of the clump. These harvesters cut mostly the outer shoots or culms, thus forcing new growth to occur inside the clump. This produces crowding, which in turn causes the newest shoots to weave through the existing culms. Consequently, only the culms at the outer fringes of the stand are accessible.
The first step in creating an accessible ring formation of the clump is to clear enough space around the clump to remove the branches from the cut culms with pruning shears or a machete and get them out of the working area. The culms can then removed with a small chainsaw, or cordless reciprocating saw if the bamboo is not too large. A wrench and straps are sometimes needed to extract the tangled culms one by one, cutting a patch toward the center.
Wild, unmanaged clumps are dangerous and difficult to harvest. These wild clumps are full of dead standing culms, many of which are ready to break. One can expect the tops to fall like deadly spears. A hard hat should be worn at all times.
A clump manager can expect to remove 2/3rds of the unmanaged culms. Among the pieces extracted, the selection for usable pieces is made. For maximum structural strength, one must look for culms three to eight years old; three to five years being ideal if they are to be treated; and five to eight years if they are to be untreated (which is not suggested).
How does one determine the age of a culm? The youngest (zero to twelve months) will have the sheaths still attached or in the process of falling away. One to two year old culms will have a clean look often with white powder on the surfaces. The mature three to six year old culms will have moss and/or fungi growing on them, particularly around the nodes, but will still have thick foliage on the branches,depending on the growing conditions. Older culms will be recognizable due to sparse foliage and yellowing upper sections.
Finally, attention must be paid to damaged culms. Look for black triangular cracks, holes, and serious rub marks that scar the surfaces. Often this type of problem will cause sap or water to leak into the interior internode chambers. To be healthy and strong, those chambers are usually dry and sealed from atmosphere during the life of the culm. They should be whitish in color on the interior surfaces. Cut any damaged portion out of the culm and use only the remaining healthy material for best results. The damaged poles could be used for temporary projects such as a trellis or garden fence.
When we need to depend on the durability of our bamboo projects, we must insure that the bamboo will not be susceptible to damage by insects or fungus. There are many approaches to treating bamboo, depending on factors varying from the size and scale of the project to the required degree of durability. Budget and, sometimes, availability of materials and supplies also affect the choice of technique.
A native Hawaiian friend once said that in the old days Hawaiians cured their “ohe,” an endemic Hawaiian bamboo used mainly for making nose flutes, by selecting only old culms that were dying. These would cure without cracking and bugs did not bother them.
Authorities say that in order to prevent bug infestation, the best time to harvest is when the shooting is finished for the year. Bugs are after the starch, which is at its peak during the shooting season.
Here in Hawaii, some bamboo varieties shoot year round, but close observation reveals a cycle of peaks and lows. Dull mossy culms with good foliage and with little or no new shoots in the clump are therefore best qualified for treatment. Sometimes the shooting culms that have not foliated will "pause" until enough sap is present in the clump to support continued fill out growth. This is still fine for harvesting as long as the clump has sufficient foliage for supplying starch without the culms you intend to remove.
Fungus is the most persistent problem, especially in the wetter climates of Hawaii. Only the most deadly treatment solutions stop fungus completely. However, we recommend using treatment that is not harmful to the environment. The use of boron salt solution as a preservation also inhibits fire from starting or spreading in bamboo utilized structurally. Light sanding and coating the dry poles with an appropriate finish will also contribute to deterring fungus.
Bucket Respiration Dip
This method requires freshly harvested bamboo to be submerged, base end down, in a 5 gallon bucket filled with a 10% solution in water of a fertilizer called “Solubar” (made by U.S. Borax and sold by Brewer Environmental Industries). The bucket must contain enough treatment to enable the bamboo’s natural transpiration process to continue until, with a pumping action, the solution reaches the leaves. In order to create the flow upwards the culm needs branches with leaves. The culm needs to remain in the solution until leaves are dead. Be sure to minimize the dilution of the solution by rain.
Some cultures traditionally treat bamboo simply by submerging the culms completely in water, salt water, or limewater. For this type of treatment, we recommend total submersion for one month. This will simply make the bamboo taste bad to the beetles.
Vertical Soak Diffusion (VSD)
The Environmental Bamboo Foundation in Bali has experimented with a new treatment method with testing that indicates excellent penetration and retention of treatment solution. They use “Timbor.” Vertically stacked bamboo timbers are filled with treatment solution after rupturing all but the last diaphragms. Fourteen days are allowed for the solution to diffuse from the inside walls In this method, the culms are filled with the base end up. A downloadable pdf document can be accessed at bamboocentral.org/VSD_Files/VSD_English/treatment1us.html
Pressurized Sap Displacement
Also known as the Modified Boucherie, this method of treatment pumps a chemical liquid into the open vessels in the walls of the culms, replacing fresh sap as soon as possible after harvest. Bamboo sap gels to protect the culm by sealing wounds with it. The culm selections should be mature enough for strong wood but not so old that the sap flow is diminished and therefore slowing treatment intake. In addition, if there is damage anywhere along the culm, especially old wounds, this will interfere with flow and dispersion into the storage cells of the culm walls in the damaged area and directly above. At the next node the sap will, in some cases, redistribute to include the entire culm through the transporting vessels.
Because pests feed on stored starch, the treatment must disperse from the vessels, which are concentrated toward the outside, into the surrounding storage cells, which are concentrated toward the inside.
It takes one to twenty four hours for the treatment to be pumped from the base to the top, and into the storage cells depending on the length, taper, and culm age. Once the treatment reaches the far end, it will take at least an hour or more to insure adequate dispersion, depending on the drip rate. Older culms will take longer to absorb the treatment solution.
Any liquid heard inside the internode chambers is a sign of possible damage to that portion of the culm, This liquid should be removed so that the portions above and below can be treated separately and, hopefully, effectively.
During the past 8 years, we have used the “Modified Boucherie” system with 10% of “Timbor,” a solution of boron salt and boric acid, made by U.S Borax.
We have harvested circumstantially in the past during shooting season with high starch content in the bamboo. This produces a worst-case scenario especially with the starchy bamboos such as Beecheyana and Vulgaris. Even with vigorous treatment protocol powder post beetles will bore in the walls sensing the starch inside, but subsequently die. Powder post beetles do not attack some bamboos, such as Bambusa Hirosi, regardless of when they are harvested. This could be due to other natural occurring chemicals such as cyanide, which make it undesirable in tasting to pests and humans alike.
Fungus growth seems to be a more difficult challenge to prevent than insect attack to both the exterior and interior surfaces of bamboo therefore we are currently recommending the following precautionary procedures to insure long life for bamboo utilized for structural purposes.
1.) Using the pressurized sap displacement method should include solution accessibility to interiors as well as the walls by rupturing the septums (node diaphragms). Using the dip method drill access holes through the walls into each internode chamber.
2.) Avoid harvesting during the shooting season.
3.) Do not be overly concerned about a few powder post-beetle holes. If there are several clusters of holes this would indicate structural damage.
4.) Surface fungal growth of black or orange indicates serious infestation. Early eradication is recommended.
POST - TREATMENT
Though there are several different ways to cure bamboo, we use the air-drying method exclusively, as do most bamboo processors around the world that we have seen.
Vertical stacking is a common commercial practice, to facilitate sorting and for even drying evenly. Keeping the culms out of direct sunlight will prevent cracking unless there are extreme temperature variations. Air circulation is very important to inhibit fungus growth and speed up moisture loss.
Rain and relative humidity affect successful curing. Surface water causes the treatment to leach. Even high humidity will produce a favorable environment for fungus growth. Fungus causes decomposition. The black fungus will grow anywhere on the culm surface where there is no silica, or preservative, and during extended exposure to the elements. Silica is the shiny coating that covers the outer walls. Orange or pink fungus on the surface indicates an interior infestation problem, usually causing structural damage within a short time.
In the dryer parts of the Big Island, where we get ten to fifty inches of rainfall, we can expect adequate open air curing in two months. In areas of greater rainfall (100 inches and more), six months is a minimum curing time. Fully cured bamboo usually turns to a very light yellow color.
Heating culms evenly with a torch or other means speeds the drying time, tempers the wood, and can produce a deeper color. In some oily varieties of bamboo, heating causes the natural oil to come to the surface. This also helps with the durability and facilitates surface coatings to stick when sanded.
For exterior use, after curing, fabrication, and sanding, all surfaces should be coated with a sealant of some kind. We started using Cetol 1, made by Sikkens. It is expensive but has the reputation for being the highest quality alkyd resin coating for durable exterior use. We have experimented with many coatings. Water based urethanes are fine for interior use. In wet climates oil based coatings will allow fungal growth unless a fungicide is added, but it is still sketchy for either interior or exterior use.
A deck coating, preferably with pigment of some sort, should be applied whenever using bamboo in direct contact with the elements. Pigmented epoxy and polyester resin are also possibilities for exterior use. Keep bamboo away from grade, or concrete. Never allow the base of bamboo posts to remain wet, in any case.
One great advantage to building with bamboo is that from harvesting to fabrication no heavy machinery, or power tools are necessary. The joint called "fishmouth" in South America provides a good load bearing surface between perpendicular bamboos being put together, where the "mouth" of one wraps around the side of the other. This joinery technique only requires a handsaw chisel and hammer or mallet. Perfecting this technique takes time. There are also power tool ways of doing the same joint but a proficiently skilled craftsperson can produce this faster and much cheaper than modern techniques.
Once the joint is made there must be a way of fastening the parts together. Three options are; (1.) Rope lashing with cross pin, (2.) eyebolt with cross pin, and (3.) flat strap with screws. Check the book list for illustrations and more in depth coverage of this. BVH will be offering workshops in the near future where we will build structures using these and other joinery techniques. This information will be given on the ”news” page. The Simon Velez system includes filling the adjoining internodes with mortar for added strength.
Bolting or lashing together perpendicular poles, where they join at the sides, works but doesn't compare in strength to the previous method. It does create a beam, much stronger than separate poles, when used for stacking or bundling parallel poles as demonstrated in the works of Velez.
The final type of joint discussed at this time is an adaptation of the current way dimensional lumber is effectively joined in developed countries. Metal brackets are configured to join the irregular surfaces of bamboo to each other incorporating steel fasteners. There are a few designers around the world with ideas along these lines. These brackets could make building with bamboo much less labor and skill intensive, therefore reducing the overall cost dramatically. While it is more industrial in appearance it can work very well.
Wall and Roof Systems
Builders can use any existing system with some success but we recommend materials that have the ability to conform to the natural irregularities and shape of bamboo.
1.) Corrugated metal
2.) Rubber over plywood (bamboo tile for top layer a possibility)
3.) Canvas and lashing Ferrocement
4.) Reinforced foam
2.) Woven bamboo mats (plastered or seal coated)
4.) Split bamboo (either woven or laid flat)
We are currently developing systems of building that will enable builders to expand these concepts into a new industry. Until we have more long-term test results for our local species and treatment methods, we recommend using bamboo as a building material for temporary structures only. We have produced such structures consisting of our own treated local bamboo, covering them with vinyl canvas.
For increased durability, bamboo should be of the best quality timber-grade, treated culms in a redundant construction system where exterior members can be easily replaced, when necessary, without jeopardizing the integrity of the structure in the process.
In order for building officials to approve structures supported primarily by bamboo, the material must be standardized in a manner similar to wood. This requires extensive strength testing of species to be utilized. With known structural values, calculations can then be made by structural engineers and architects.
This process is underway by others around the world. Counterparts of ours on Maui have submitted bamboo grown in Southeast Asia to the International Council of Building Officials (ICBO) for testing. With further cooperation from Research and Development, our local universities, and other grant sources we can begin a study of our local species for future ICBO consideration .
Our research and experimentation continues to find more cost effective methods of constructing with bamboo. We are looking forward to seeing bamboo included in the Uniform Building Code so that everyone can benefit from the strength and beauty of bamboo, bringing to our built environment an appropriate tropical island style.
SUGGESTED BOOK LIST
ASTM. 1991. American Society for Testing and Materials. Standard method of laboratory evaluation of wood and other
cellolosic materials for resistance to termites. D3345-74 (reapproved 986). Annual Book of ASTM Standards, Vol. 04.09(Wood).
ASTM, West Conshohocken, PA.
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