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January 2012. An unusual request from a member working in the Himalayas, in remote tribal villages of Northern Sikkim where on 18 September there was a 7.6 strength earthquake. Several people died and several hundred houses made from stone were no longer fit to live in. Traditionally bamboo was used for making houses. After the devastation caused by the earthquake, people are rethinking to use bamboo oncce more. Information is needed how the bamboo can be treated so that it avopids being consumed by insects.
Members made a number of suggestions:
1. Bamboo and insect attack. The insects in the area mentioned were not know, but borers and termites are found in Darjeerling (there are control programs for termites in tea plantations), but they are limited by elevation. Bamboo has no resistancw to either borer beetles or termites.
Borer beetles, like some rot fungi, are more reliant on sugars and starches in wood and bamboo than termites. Attack on bamboo can be lessened, but not completely stopped, by removing the sugars and starches through soaking the bamboo in water, or by cutting the bamboo when these components are naturally low.
Termites depend on the cellulose (mostly, but also lignin), and thus termite attack is related to neither sugar nor starch content.
The hard exterior is more difficult for termites to penetrate than cut edges, so they prefer the latter to the former to enter the bamboo, but they will easily attack through the exterior.
There are many chemical treatments to reduce rot, borer and termite attack on bamboo; most (if not all) adapted from wood preservatives. Of the many that can be considered (synthetic pyrethroids are probably the most effective), borates are cheap, common, effective and easy to apply through soaking (and so can be applied when soaking to remove sugars and starches). However, borates leach rapidly when exposed to water. Therefore they are recommended for wood preservation only when the wood is not in contact with the ground. Borate treated bamboo may be a useful wall if erected upon a concrete slab foundation. Given the monsoon, the exterior walls will probably need reapplication of borate solution (e.g. with a paint brush) each year.
An alternative is to make a composite material with wood or bamboo and cement (this has received a lot of attention in Indonesia, Malaysia and the Philippines). These composites are cheaper and lighter than concrete or bricks alone. The composites have mixed results in tests against rots and termites; they are attacked but much less so than wood or bamboo alone. Resistance can be increased by reducing the proportion of wood or bamboo, or adding preservatives or insecticides. Also, the wood or bamboo should be soaked to remove sugars as these retard the setting of the cement.
2. Pacific: It was agreed that the main problem in Pacific Isalnds with bamboo construction is with borer beetles. Ground contact is not an option as bamboo rots quickly in contact with moist soil. Wall materials are made from weaving split bamboo into large mats. A double layer makes an almost light proof wall. Each of the bamboo wall layers is woven at a different angle. One vertical/horizontal. The other diagonally. The bamboo walls are fixed between wooden structures and corrugated iron is used on the roof. The house is very strong and yet relatively lightweight. When split and woven into mats, the interior of the bamboo material is more absorbent and can be treated using permethrin plus an oil based penetrant such as kerosene. This will extend the life considerably. Absorption may vary with different bamboo species. The exterior surface of the bamboo is hard and shiny and relatively impenetrable to insecticide treatments. Probably also to insects.
3. Some references:
Ashaari Z & Mamat N (2000) Traditional treatment of Malaysian bamboos: resistance towards white rot fungus and durability in service. Pakistan Journal of Biological Sciences 3: 1453-1458.
Febrianto F, Sahroni, Hidayat W, Bakar ES, Kwon G-J, Kwon J-H, Hong S-I & Kim N-H (2010) Properties of oriented strand board made from Betung bamboo (Dendrocalamus asper (Schultes.f) Backer ex Heyne). Wood Science and Technology 46: 53-62.
Okahisa Y, Yoshimura T & Imamura Y (2006) Seasonal and height-dependent fluctuation of starch and free glucose contents in moso bamboo (Phyllostachys pubescens) and its relation to attack by termites and decay fungi. Journal of Wood Science 52: 445:451.Garcia CM & Morrell JJ (2010) Wood Science and Technology 46: 53-62. Efficacy and economic benefits of prophylactic treatments of newly felled bamboo. Journal of Economic Entomology 103:101-107.
See also the Environment al Bamboo Foundation www.bamboocentral.org/index1.htm, and the International Network for Bamboo and Rattan http://www.inbar.int/Board.asp?Boardid=67 has a section on sustainable buildings. Under Global bamboo housing program it mentions houses of bamboo withstanding damage in the epicentre of a 7.6 magnitude earthquake in Costa Rica).
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