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Construction with Bamboo
Diplom-Ingenieur Christoph Tönges
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basics
Purchase

There are many bamboo dealers usually located near small urbanizations. With the introduction of modern but expensive building materials like brick and reinforced concrete, the "cheap" bamboo became the building material of the poor. At present, a change of this view takes place again. This development is favored by popular projects of the architect Simón Vélez, but also since handicraft and furniture industry discovered the material for diverse uses.

Simple bamboo dealer
 (29) Simple bamboo dealer
 
Specialized dealer

Because of the increasing demand for selective use, there are more and more specialized dealers. The raw material is partially from plantations, the culms are pre-sorted and optionally immunized.

 (30) Specialized dealer
 
Storage and Desiccation

Sometimes the hollow culms of the recently felled bamboo are filled up with water. Therefore they must be dried slowly first before they are graded according to curvature, diameter, weight and sound test. Bamboo for sale has been cut two or three months before. At this time its relative humidity is approximately 30 to 50 percent.
By air in shade desiccation, the relative humidity of the culm decreases to the humidity balance of approximately 15 percent. In order to avoid deflection of the culm after harvesting, they are stored horizontally. They should be protected against sun, rain and moisture; racks are most suitable, they provide good ventilation.

Storage
 (31) Storage
 
Traditional storage

Traditionally they are also stored and dried standing upright. The desiccation by air lasts four to six months according to the climate. The desiccation in an oven lasts only two to three weeks, however, rips and splits may occur.
Because of the fiber structure the shrinkage behavior is different to wood. If Guadua is dried from 140% to 20% moisture content it dwindles ca. 0,3% longitudinal, ca. 5% in cross direction and ca. 10% in tangential direction. Timber, dried from 30% to 1% moisture content, dwindles axial / radial / tangential:  0,3% / 3,7% / 7,5%. The highest shrinkage is in the aeras of soft fibers: bamboo inside, timber outside.

 (32) Traditional storage
 
Timber protection

Bamboo can be attacked by fungi (in particular if the moisture content (MC) lies over 18 percent), by woodworms and termites (the critical MC area lies between 12 and 18 percent). They damage the structure to such an extent, that parts have to be exchanged or become useless. Some bugs (Dinoderus, Bostrichidae, Lyctidae) cause large damage by perforation to felled and living culms as well.
To extend lifespan of bamboo constructions, it is important to keep an eye particularly on constructive moisture protection, for example cantilever roof and moisture barrier in the wall against rising ground moisture.

Click to enlarge!
 (33) Insects of the habitat Guadua
 
Old bamboo construction

The chemical wood protection is more expensive, so it is only recommended objects with special uses and intended for longevity. To apply wood protection to the inside of the culm wall, either all internodes have to be drilled from outside (for the injection) or all diaphragms have to be pierced (watering).
Constructive protection effectively keeps away moisture from a bamboo construction, so the longevity can be significantly increased.
Constructive bamboo protection is a century guarantee for this material; there are constructions with undamaged Guadua in Manizales (COL) which are more than hundred years old. The experience of many years of craftsmen and architects guarantees longevity, under consideration of all these conditions.

 (34) Old bamboo construction
 
Methods to extend lifespan:

Harvest time

The harvest of Guadua proved to be favorable if it takes place one week after full moon. At this time there is less capillary water in the culms due to the weaker gravitation of the moon. This has two advantages: on the one hand the bamboo is not so heavy and on the other hand it dries faster, thus tends less to tearing.

Transport of the harvest
 (35) Transport of the harvest
 
Still green Guadua

The branches together with the leaves should remain on the culm at first, to remove the free capillary water using the natural evaporation process (bound water is in the cells); unfortunately this is often neglected for "commercial" reasons. On the basis of photosynthesis, in the course of the morning the bamboo transports starch from the roots into the leaves, furthermore there is more water in the culm (weight! > gross density). If the harvest therefore takes place before sunrise, the starch is still in the roots. The more starch is in the culm, the more nutritious and attractive it is to wood-eating insects.
The Paez-Indios in Tierradentro (COL) harvest in the afternoon because at that time the starch is in the leaves and less water in the culm, respectively.
If the culm is cut a.m., this can be recognized by strong insect attack after some time.

 (36) Still green Guadua
 
Fumigate

If bamboo culms are fumigated (the own branches and leaves are used for this) for a longer time, they become inedible to insects. The culms are smoked with an air temperature of 50 to 60 degrees Celsius and changing air moisture. The goal is to prevent the tar from condensation, so that it can ingress into the fibres in a gaseous condition. This is gained by shifting between smouldering (tar production through pyrolysis) and heating fire.
This procedure is mastered especially well in Japan.
The culms must be pierced perforated before; however, the holes must not lie in a line since there is the danger of tearing by desiccation. The disadvantage of this method is that the culms smell awful afterwards.

Fumigator
 (37) Fumigator
 
Watering

Watering
Watering is frequently used. The fresh poles are stored 4-12 weeks in stagnant or flowing water. Starch, carbohydrates and other water soluble substances get fermented or are washed out.

Boiling
15 - 60 minutes of cooking is another method to get nutrients, carbohydrates and starch out of the bamboo.

Heating
Short heating up on 150C of the bamboo culm changes slightly the structure of the outer tube wall, so that a certain resistance against insects is gained. Disadvantage: The poles can burst in the heat.

 (38) Watering
 
Watering with Borax

Borax is no insecticide (natriumpentaborat + boric acid). The effect is that the crystals immediately destroy the digesting insect stomach!
For this treatment the diaphragms of the culms must be pierced with a long iron pole at first. The diaphragms at the lower end of the culms are very strong so that the first has to be broken through with a hammer. This first hole helps piercing further.

Piercing of the Diaphragmen
 (39) Piercing of the Diaphragmen
 
Dip tanks

There are different ways to immunize the prepared culms. Frequently, a basin is used immerse the culms. It is important to prevent the culms from surfacing, so that they will stay completely dived.
In Indonesia, the culms are put vertically and then are filled. The lowermost diaphragm must remain undamaged until the borax solution is left out at the end. A very economical and efficient method, considering in particular, that because of the evaporation of the water the true borax solution ratio in the basin can never be known exactly.

 (40) Dip tanks
 

The solution can also be injected through before drilled holes.
In this case the holes must not lie in an axial line; otherwise the tube might split there.

Injection
 (41) Injection
 
'Bouchery-Modificado'

In Costa Rica an installation ('Bouchery-Modificado') has been developed, with which it is possible, to press the wood preservative with high pressure into the bamboo (Gonzales/ Janssen).

For construction projects situated higher than 1000 m above sea level (no termites!) Jörg Stamm recommends a solution of four to five percent with an immersion duration of four to five days. If the attack of termites has to be expected, a sufficient protection is attained with a solution of 10 percent.
Borax enters the cells of the bamboo culms through osmosis. After watering the culms are two to three times heavier than before, so they must be dried again in order to use them for construction purposes.

 (42) 'Bouchery-Modificado'
 

Coatings

Lime sludge, lime and cow dung, kreosat, Rangoon oil.
Jörg Stamm uses a cream of wax (wood care) with tar solved in paraffin. This is a ancient recipe from the Lebanon. With this paint the bamboo culms develop a very attractive dark brown patina. The painting procedure must be repeated regularly according to sunlight and driving rain load.

Insecticides

Ecologically and hygienically very dubious impregnations against insects and vegetable pests are BHC, PCP, kerosene, DDT, DDT-containing diesel, naphthalene, formalin, dieldrin, phosphates and varnish. Unfortunately, they are still frequently applied, particularly in handicraft and furniture production - importers therefore should aim for relevant information.

Patina
 (43) Patina
 
Processing with chisel Tools and processing

Bamboo can be processed with the simplest tools, like machetes, saws, chisels (for example to make a 'fish mouth'). Since the silicified outer part of the tube is very hard, tool wear is somewhat higher compared with processing timber.
Generally Guadua is comparable with oak and maple on the basis of its gross density (790 kg/m³) and its hardness ('Brinell'-hardness grade 4.0). Therefore, the manufacture of clean (thus durable) connections requires very sharp tools with high durability.

 (44) Processing with chisel
 

Cutting and carving

In green condition bamboo can be cut well with the machete; later in dry condition sawing is recommended. Ornaments and patterns can be made by carving with knives.

Sawing

Because of the hardness of this material, hack saws are recommended. Conventional hardened steel is also a proper tool, but their wastage is clearly higher. When sawing bamboo tubes 90 to the roll axis, the cutting direction of the saw teeth are to be taken into account, since there is the danger of fraying the surface (turn tube or saw to avoid this!).

Circular saw
 (45) Circular saw
 
Annulus cutter Splitting

Due to the axial fiber alignment, the bamboo tube can be split fast and cleanly with a wedge.
In Asia the bamboo tubes are split in eight to twelve strips with a annulus cutter to fabricate laminated floor coverings. (>Production method and machine)

 (46) Annulus cutter
 

Breaking

If the bamboo is broken it is not possible to use it as a building material any more.
The broken outer fibers are razor-sharp because of the silicified layer and therefore easily lead to injuries.

Guadua culms are broken, in order to use it as mats, for example as plaster base (Production method).

Breaking open Guadua
 (47) Breaking open Guadua
 
Special drill Drilling

Stone and metal drills are very suitable because of their higher longevity.
For bolting a 0,5 mm larger hole diameter is recommended.

A special drill is suitable to produce a 'fish mouth'. The diameter of the drill should correspond to the diameter of the culm at which it is connected.

 (48) Special drill
 

Cold bending

Because of the high elasticity of bamboo, bending. is possible. With increasing diameter and wall thickness, the bamboo tube must be dried. pre-curved directly after harvesting. Convex grown bamboo tubes are sorted out after harvest and are used for accordingly bent parts.
To attain culms with a square cross section a casing box, is put on a young shoot. The once adopted form does not change during life time of this culm.

Warm bending

Heating a bamboo workpiece on 150 C, it becomes plastically deformable. It keeps its new form When cooling down. (>Production method)

Cold bent!
 (49) Cold bent!
 
Bibliography
Links

The Chinese philosopher Konfuzius said:
"Without meat, we can live,
without bamboo, we must die."

home    
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NEW >>> www.bambus-conbam.de <<< NEW
Author and Copyright: CONBAM
Translation: Victor Löffler --- 06.08.2002 --- last update: 23.07.2005