General Properties of Bamboo and Maintenance Tips
Bamboo is often described as very durable, however, this is primarily in reference to the sustainable growth of the bamboo plant, and not so much about the durability of the bamboo stems.
Proper use, treatment, maintenance and care can ensure excellent durability because there exist bamboo structures of more than 200 years old, but it is important that the end user is properly informed to make the most of his / her bamboo products.
What is Bamboo?
Bamboo belongs to the family of grasses and doesn't have the same properties as regular wood. Worldwide there are about 130 herbaceous and 1,450 woody bamboo species known.
Bamboo is anatomically and morphologically very different from normal trees. A bamboo plant has a stem, branches and leaves but that's where the comparison with trees end. Bamboo is hollow, has no bark or year rings, and doesn't increase in diameter as the plant gets older.
Bamboo stems grow on average 25 cm per day, and reach their maximum height in just 6-7 months (some tropical bamboo species grow up to 30-40 m).
Bamboo stems are mature and ready for harvest in 3-6 years, after which new bamboo shoots will develop naturally. Because of its amazing growth rate, its 1001 different uses, and the fact that bamboo plants keep emerging without re-planting, it is considered a very sustainable resource.
Is Bamboo Durable?
Unlike other timber varieties like teak, bamboo doesn't posses toxic deposits that can help against biodegradation, therefore the natural durability of untreated bamboo poles is low. For most species less than 2 years, and 4-7 years under ideal conditions (without exposure to sun and rain). The preservation of bamboo poles is therefore essential to extend its service life.
The large amounts of starch present in bamboo makes it highly attractive to mold and fungi, termites and powder-post beetles. They cause much damage during drying, storage, and subsequent use. Bamboos also have minor amounts of waxes, resins and tannins, but none of these have enough toxicity to improve its natural durability.
Because of its low natural durability, bamboo poles should be treated against potential insect contamination immediately after harvest. One of the most used and effective preservation techniques is to impregnate bamboo fibers with a mixture of borax or boric acid minerals.
Once all natural sugars in the bamboo fibers are replaced with salts, they become immune to insects. Treated bamboo poles have a service life of 50 years or more, assuming that they are kept from direct contact with sun, rain or soil.
Additional maintenance and care is required by the end user when using bamboo poles for outdoor applications. This is discussed much more detail in the final section of this article.
Why does Bamboo Crack?
An important feature of bamboo is the way it reacts to different temperature or humidity changes, as this may result in splits or cracks in the bamboo pole. To understand why this happens we'll have to look at the anatomy of bamboo.
1. Anatomy of Bamboo
Bamboo is an anisotropic material, that is to say that the properties in the longitudinal direction are completely different than those in the transverse direction. The longitudinal direction is made from bamboo cellulose fibers which are strong and stiff. In the transverse direction bamboo consists mainly of lignin which is soft and brittle. Therefore, bamboo is a one-sided reinforced composite with relatively little tangential capacity.
The shrinkage of the nodes is 4 x higher than the shrinkage of the internodes (hollow portion between two nodes). This may be the result of a larger amount of reinforced fibers, which are customary in the internodes but less in the nodes.
Because of the differences in anatomical structure and density, there is a large variation in tangential shrinkage from the inner (10%) up to the outer part (15%) of the culm wall. Thus, the tangential shrinkage is higher in the outer parts of the wall than in the inner parts, which can lead to cracking.
2. Equilibrium Moisture Content of Bamboo
Bamboo is a hygroscopic material which means that it will absorb or expel moisture from or to its surroundings until an equilibrium is reached. The moisture content thus varies according to the properties of the surrounding air.
Water is held in bamboo in two ways; free water which is retained in the cell cavities, and bound water which is retained in the cell walls themselves. The moisture content of the culm wall is higher in the inner portion than in the outer portion. The nodes have lower values than the internodes. These differences can be up to 25%.
During drying bamboo loses free water until its moisture content is about 15%. The bamboo will shrink if the remaining water is driven out, but the bamboo can swell again after drying when moisture is recovered from the relative humidity of the surrounding air.
Bamboo will therefore shrink and swell according to changes in relative humidity. Splits and cracks may then occur due to stress caused by sudden drying and direct exposure to the sun.
Why does Bamboo Weather?
Just like any other wood products used for outdoor applications, bamboo will weather over time.
Weathering of exposed bamboo occurs as a result of the interaction between different climatic conditions, such as variations in temperature and relative humidity.
Repeated humidifying and drying of exposed bamboo creates tiny cracks in the surface of the bamboo. UV rays cause the breakdown of the cellulose layer, and finally, wind and dust particles have a sandblasting effect on the bamboo surface. The combination of all these factors will ensure the weathering of outdoor bamboo products.
How to Maintain and Care for Bamboo Poles
Before protecting bamboo poles against weathering and cracking it is important to know a few basic rules when working with bamboo materials:
1. Avoid direct contact with soil
Avoid direct contact with soil to prevent bamboo from rotting. When installing bamboo fencing for example, it is recommended to install the fence at least 2 cm from the ground. Burying bamboo poles in the ground is not recommended, unless they are coated with special bitumen paint or tar which can offer certain protection.
2. Don't use nails to join bamboo poles
Due to the anatomical structure of bamboo fibers, which all run in the same longitudinal direction, forcing nails into bamboo will lead to splitting. Screws can be used if a slightly smaller pilot hole is pre-drilled in the bamboo pole.
3. Handle bamboo with proper care
Dropping bamboo on the ground or hitting it with a hammer may cause cracks and splits. Therefore, bamboo should be handled and installed with care, preferably by experienced installers.
Protecting Bamboo Fencing
To avoid bamboo from weathering (and to a certain extend cracking), 2 layers of special sealer must be applied to the surface. A high quality bamboo sealer is recognized by its high resistance to moisture and ultraviolet radiation. Such stain or sealer contains a water-repellent preservative such as wax, paraffin wax or resin, and a binder which minimizes degradation, shrinkage and swelling.
A sealer that meets all these requirements is Bamboo Protector, a specially developed transparent sealer with excellent UV protection. Bamboo Protector must be applied to the bamboo surface, but also to the naturally closed nodes at the top of the bamboo fence. The sealer prevents bamboo fibers from absorbing moisture and reduces the volume and speed of moisture exchange with the atmosphere.
For optimal protection, we recommend applying Bamboo Protector annually or biannually (depending on the weather conditions) as it will ensure the longevity of your bamboo products. If bamboo fencing is well maintenance and properly installed, they can last up to 15-20 years.
Restoring Weathered Bamboo
Even if a bamboo fence is weathered, it can still be restored. Apply Grey-Go bamboo color renovator to the surface and watch how the original yellow color magically re-appears.
More information about our special bamboo maintenance products can be found in the description of each product.