Building With Bamboo Part 1

Using Bamboo For Building

Bamboo is an excellent material and widely used for building, here we look at how strong it is and how suitable for building construction and the advantages and disadvantages of bamboo. We also discuss growing of bamboo and how to select, harvest and treat bamboo for construction.

Bamboo is very versatile

Bamboo must be one of the most useful and widely used plants in the world. Technically speaking, a type of grass, bamboo is used as a construction material for everything from houses to industrial buildings, bridges to henhuts.

It can be used for columns, beams, flooring, roofing, walls, window and door frames, doors, ceilings, blinds and screens, pipes, gutters, fences, and scaffolding. It is even being used to replace steel to reinforce concrete.

There are of course a million and one (why a million and one I don't know) other uses for bamboo such as ladders, textiles, paper, musical instruments, furniture, fishing rods, food utensils, baskets, handicrafts, water filtration and even weapons (ever seen a bunch of kids with a Nyepi cannon). The chinese eat bamboo shoots and feed the leaves to their pandas. In a world rapidly running out of wood we can only expect there to be an ever increasing world demand.

Advantages and Disadvantages of Building with bamboo

Advantages

As a building material bamboo offers many advantages:

As a building material it is very strong with excellent tensile strength.
It flexes which when used in structures gives it earthquake resistant properties.
It can be easily worked using simple tools.
It can be readily used in its natural state but becomes even more useful when machined and laminated to form beams, planks or sheets.
It grows very quickly.
It grows in many parts of the world.
It is cheap.
Bamboo is surprisingly dense and heavy, pick up a laminated bamboo chopping board and you'l know what I mean.
It can be a beautiful material to look at particularly when well worked and finished.
It is environmentally very sound being biodegradeable, quickly and easily renewable and an excellent sink for carbon.

Disadvantages

It is a grass, and has a limited life being susceptible to pests and fungal attack if not treated.
Like all grasses it burns easily when dry.
When used in its as grown form its shape requires careful building design.
It can crack if not handled or dried correctly or used in a poorly designed structure.
Being widely accessible as a low cost , material for poor people it is widely considered a 'poor man's' building material.

Growing bamboo

Bamboo grows from seed to form clumps. The lifespan of a bamboo clump can be anything from 50 to 150 years at the end of which they flower and die off.

Within each clump are the bamboo poles or culms as they are called. As the culms grow to maturity they die off and new culms grow to replace them.

The life cycle of an individual culm is generally around 5 to 7 years. Bamboo is one of the fastest growing plants on earth some varieties having been known to grow up to a metre in 24 hours and reaching up to 30 metres tall and 20cms in diameter. A more typical growth rate is around 10 cms per day and up to 5 to 12 metres high.

During the wet season a culm can grow to full height and diameter in only 3 or 4 months after which they progressively dry out and strengthen over the next couple of years reaching their full strength and maturity at around 3 to 4 years old (the best age to cut bamboo). From there on they decline with age and rot.

Each culm is a tube with internal dividers or nodes spaced along its length. The culm tapers along its length becoming narrower towards the top. The length, diameter, distance between nodes and amount of taper varies considerably between different species. Of particular importance is the thickness and density of the wall of the tube. Some species have very thick walls making them very strong but are also much heavier than other species.

Selecting the right bamboo

It is important therefore to select the right bamboo for a particular purpose and with around 1,500 species we have plenty to choose from. We have to consider the length we require, the diameter, wall thickness, the distance between the nodes and the density of the wood. We also need to consider how straight it is, some species can grow very straight while others are as knobbly as a goblin's nose. For decorative purposes there are also coloured varieties in black, white and mottled.

It all sounds a bit daunting but fear not, there are several commonly used varieties here in Indonesia which include from best to worst:

Ori and Gombong (best)
Petung
Legi
Wulung
Apus (worst)

Apus is the cheap stuff used for scaffolding, it splits easily, is low density and absorbs moisture easily which can make it split as it dries out.

Petung is probably the most widely used in building. It comes in a large diameter 15 to 20 cms with a good wall thickness and is mainly used for columns and beams. It also comes in a smaller diameter and both black and the usual straw colour.

Ah but how long will it last?

The life expectancy of bamboo varies enormously depending on its species, how it is harvested, transported, cured, treated, stored, handled, used and maintained. All aspects are important and even well treated bamboo won't last long if is badly handled or used in the wrong way.

Harvesting bamboo

As we have said bamboo should be harvested when the wood is at its maximum strength, usually between 3 to 5 years old. It is best to harvest bamboo with the least amount of sap in it to minimise the sugars and starches that attract pests and fungal growth. The best time is in the dry season, during the period of the new moon and in the early morning or evening.

Treating bamboo

After the bamboo is cut as much of its sap is removed as possible. A traditional method is to lie the freshly cut bamboo in a flowing stream for several weeks to leach out the sap replacing it with water.

Another method is to stand the bamboo upright in drums of water for several days. The bamboo draws in the water and exudes the sap.

Yet another method is to inject water under pressure into the end of the culms to force the sap out.

Untreated bamboo will, like any grass, not last long. For short term purposes such as scaffolding or buildings for temple ceremonies the bamboo is not treated and may only last 2 or 3 years. Good harvesting and treatment can extend the life up to as much as 20 or 30 years.

Treatment provides protection against the natural enemies of bamboo, termites, powder borer, fungus and wet rot.

The best treatment method for bamboo as recommended by the Gajah Mada University in Yogyakarta involves boiling it in a bath of preserving chemical for several hours (usually around 12 hours). The structure of the bamboo swells and absorbs the preserving fluid. After treatment the bamboo cools down and dries out trapping the preserving chemical within the bamboo structure. The most commonly used chemical is a combination of borax and boric acid although some chemical companies are now supplying more sophisticated preserving agents.

A simpler and more commonly used method, though not as effective, is to stand the bamboo in drums and pour preserving fluid in at the top of the culm. The bamboo is left to soak for several days.

Another method is to pressure inject the preserving fluid into one end of the bamboo forcing it right through the length of the culm.

Some people use more aggressive chemicals but great care should be taken. Deldrin and ddt are considered very nasty these days and should be avoided.

Once treated the bamboo is dried slowly and evenly in the shade to avoid cracking in the outer skin. Care must be taken as the bamboo can split if it is dried too quickly. Air drying may take 6 to 12 weeks though this time can be reduced by slow kiln drying over 2 to 3 weeks.

So if you want to go back to nature you too can live in a grass house and bamboo is the grass of choice.