The Shelter and NFI Sector in Cox’s Bazar, Bangladesh have asked Arup to produce a Technical Guide on the durability and treatment of bamboo for all structures (shelters, community facilities and bridges) in the refugee camps and sites in Cox’s Bazar. Bamboo is currently being used as the primary construction material for nearly all structures in the camps because it has been readily available, however it is naturally vulnerable to insect and rot attack, more so than timber. Durability is the main reason why bamboo is considered a “poor man’s construction material”, and why so many bamboo structures do not last. Without consideration for durability, some parts of the existing structures will deteriorate in as little as 6 months following construction, leaving them more vulnerable to wind and structural failures.
This guide has the following aims:
Provide information on the natural durability of bamboo, and the three main causes of decay in bamboo: termites, beetles and fungal attack (rot).
Discuss the main options for improving durability, recommending the most appropriate for Cox’s Bazar.
Discuss the main treatment methods using boron, recommending the most appropriate for Cox’s Bazar.
Challenge a number of misconceptions regarding the durability and treatment of bamboo.
It is recommended to read this guide in conjunction with the Humanitarian Bamboo guide (Humanitarian Bamboo, 2009).
The two key recommendations for improving durability of bamboo in Cox’s Bazar are presented below, in order of priority and impact. Both are required (introducing one does not negate the need to have the other):
Incorporate durability by design, in particular by the use of footings to isolate the bamboo frame from the ground, and by creating as watertight walls and roofs as possible. This is considered as important as treating the bamboo, since even treated bamboo will still rot quickly in the ground.
Treat bamboo with boron. The most appropriate method of treating bamboo is considered to be boron. All three of the following treatment methods could work, and will be more appropriate depending on the local circumstances:
a. Cold-water bath. Lowest complexity, low output per bath.
b. Hot-water bath. Highest complexity, high output per bath.
c. Vertical soak diffusion. Moderate complexity, high output, requires high access tower and shelter, not suitable if bamboo is cracked.
Boron treatment will require tight controls over disposal of waste products. Boron treatment should use freshwater – the use of saltwater would first require a laboratory test to see if and how much the salt interferes with the solubility of the boron, which could reduce the efficacy of the treatment.
In addition to the above, the following are also recommended – these will have a smaller impact on durability, but are still worthwhile:
Select mature bamboo. Attempting to influence the bamboo supply chain by harvesting mature bamboo only. Harvesting immature bamboo can also reduce clump productivity.
Keep bamboo away from insects during transport and storage, prior to treating with boron. This can be best achieved by keeping the bamboo away from ground contract, and periodic fumigation.
Keep bamboo dry during transport and storage, both before and after treating with boron.
If boron treatment is not available:
Alternatives to boron. If boron treatment is not possible, it is recommended to attempt to influence the bamboo supply chain by harvesting at optimal times, and soaking the bamboo in fresh water for 4-8 weeks, but effectiveness will be limited.
Table 1 presents suggested approximate lifespan of untreated and treated bamboo in Cox’s Bazar, and illustrates the effectiveness of both treating and keeping the bamboo dry.
If any existing bamboo structures are experiencing issues with rot or insect attack, or there is a wish to improve their durability, in most cases it is simplest and most effective to demolish the building and rebuild.
The following methods often proposed to improve durability are not considered relevant when considering durability for this context:
• Selecting more durable bamboo species. It is not considered important to select a specific bamboo type which anecdotally may have greater natural resistance – there are much more important factors which influence durability.
• Seasoning. The bamboo used in shelters will effectively season in-situ (with the exception of the bamboo placed directly into the ground, which will rot).
Therefore, seasoning can be considered unnecessary.
• Clump curing. This has only minimal benefit, yet adds complexity to the supply chain.
• Smoke or fire treatment. This method has limited efficacy, uses valuable fuel, potentially weakens the bamboo and exposes people involved in treatment to smoke.
• Conventional paint. This provides limited efficacy against water and none against insects, and needs to be reapplied frequently.
• Painting with coal tar/bitumen/used engine oil. This provides limited efficacy against rot, is slightly more effective against insects, but is a known carcinogen to humans. Although widely used in the humanitarian and development sector, it is in fact much less effective than many believe.
• Modern preservatives. While some of these can be very effective, they are all either expensive, complex to apply or carry significant health risks during application and at end of life.