Processing Method

Bamboo Harvest and Selection

Only mature bamboo culms over 3 years old are harvested. As at this age bamboo shows reduced shrinkage and cracking when dried and improved natural strength.

Each cut culm is visually assessed and selected for straightness, thickness and node spacing. Sections unsuitable for structural use are made into smaller diameter poles or mats for minimal waste.

Preparation and Puncturing

After harvesting bamboo is cut to required lengths. Side branches are removed and all internal nodes are punctured.

Because bamboo has a naturally water resistant outer skin, preservatives cannot penetrate from the outside. So opening the nodes allows water and treatment solutions to the fibres from within.

Water Soaking and Preservation

At our processing facility, fresh bamboo is submerged directly into water without any delay or transport, ensuring the poles do not dry out first. The bamboo is soaked in flowing water for a minimum of 3 weeks. This naturally removes sugars and starches and begins a natural fermentation process.

After soaking, the poles are then treated with a low concentration borax solution, a mineral preservative. This step strengthens the bamboo’s resistance to insects and fungal attack.

Drying and Seasoning

After treatment bamboo is air dried under cover in a well ventilated shaded area to prevent cracking. Poles are propped to allow airflow.

Drying time varies depending on diameter and climate. Properly dried bamboo becomes lighter and more durable, making it suitable for use in construction.

Storage and Use

Boron treatments are non fixative, which means the preservative can leach out if the bamboo is repeatedly exposed to rain or standing water. Treated bamboo should therefore be dried and stored under cover with good airflow. From here it is ready for community building projects or small scale supply.

Full Immersion Processing 

Tank Depth

Whole culms are laid horizontally and completely submerged in the treatment bath. The tank only needs to be deep enough to cover a batch of culms together with the hold down system and a bit of space min 10 cm. Because of this, the tank should be long and relatively shallow. In practice an internal liquid depth of about 1 m. Making the tank deeper quickly increases the volume of solution required, which increases both cost and handling without improving the treatment.

Tank Lengh

For construction use it is practical to design the tank around common building lengths. A tank length of around 4 m works well for most structural pieces typically 3.5 and keeps the treatment system compact and economical. Build a longer tank of around 6.5 m if you regularly intend to treat full 6 m culms. Trying to design a single middle sized tank to do both usually creates inefficiency, more chemical volume, more cost and more difficulty handling the bamboo.

Tank Positioning 

For the treatment tanks themselves a partly recessed construction works well. A shallow tank that is slightly below ground level is easier to load and unload, while still allowing the structure to be inspected and maintained. Keeping the tank partly above ground also makes it easier to clean and to drain the solution when needed. A partially sunken structure also helps secure the tank in place.

Sap Diffusion Processing 

Natural Diffusion Alternative 

Natural diffusion can be used for freshly cut green bamboo. In this method only the base end of the culm sits in the preservative solution while the liquid gradually rises through the bamboo as the natural sap is displaced. The butt end is typically immersed about 25 cm into the solution. The bamboo is best kept close to vertical so the preservative sits evenly around the base and the liquid can move upward through the culm. This requires a tall supporting framework that holds the bamboo upright during treatment.

Buluh Bamboo™ Products