Why is it important to treat bamboo?
The natural durability of bamboo is lower than for wood and in most cases it is not long enough for an economic lifetime.
The lifetime of an untreated bamboo can vary between 1 and 15 years depending on conditions, depending on variety, if it is in contact with water and soil, under cover, humidity etc.
Due to the absence of any toxic substances, bamboo represents a ready source of food to various organisms. The presence of starch in the green or dry bamboo makes it attractive to such organisms, especially fungi and insects as borer beetles.
I do not mention here the human who also appreciates bamboo in Asian dishes but when the bamboo is in the form of shoots. As the panda that eats bamboo plant in forest but other varieties that the one we use for construction.
Bamboo is therefore subject to attack by fungi (rot, only when moist) and insects (beetles and termites). To avoid these, the bamboo must be treated. Unfortunately, it is quite difficult to treat bamboo because the external skin of the bamboo is very compact and the vessels through which any solution could be injected cover only about 10 percent of the cross-section of a culm.
How to treat bamboo?
Preservation treatment methods of bamboo are of 2 types: the traditional or non-chemical methods and chemical methods.
Others alternatives methods are rarely used, Chalet & Bamboo has developed on 100% eco-friendly method.
The choice of treatment method will depend on the state of bamboo, whether it is green or dry, whether whole cane or split, its future application, quantity to be treated and the time available.
Traditional or non-chemical methods
These are ancient methods widely used for centuries by villagers and artisans in countries where bamboo grows, and often the skills are passed on from generation to generation.
The most commonly methods used are smoking, white-washing, storage in water.
Smoking is carried out in chambers. Heat and toxic agents produced by smoke destroy the starch in bamboo making it immune to insect attack and also blackens the culms.
There are, in Japan, bamboo houses older than 100 years. The smoke from the kitchen (fireplace without chimney) spreads throughout the house and thus preserves the bamboo structure from any attack.
Baking over open fire
Baking over fire after applying oil on the surface of green round bamboos. This causes rapid drying of the outer shell and induces partial charring and decomposition of starch and other sugars. This method is very useful for simultaneous straightening of bamboos in round form.
Bamboo culms are painted with slaked lime, thereby prolonging their lifespan by delaying and reducing the absorption of moisture while being a repellent against insects.
Soaking in water:
Freshly cut bamboo is stored either in water ponds or in running water for 3-4 weeks to leach out starch. This process protects the bamboo against insects. When stored in water basins, water must be changed frequently to avoid fouling.
Although traditionally treated bamboo shows increased resistance to insects and fungi attack compare to the freshly cut culms, these methods do not however provide complete satisfaction in the long term.
Chemical treatment methods
Chemical preservatives are used to protect bamboo products from degradation. These are well established methods providing good protection even in adverse conditions.
Tanalised method - chromated copper arsenate (CCA)
As for wood, bamboo products are often tanalised, impregnatedunder pressure or by boiling with highly toxic substances such as chromated copper arsenate (CCA)to protect against rot.
TheCCA has been very effective but very toxic and carcinogenic.
Other products are used as "ammoniacal copper arsenate" or ACA. Ammoniac facilitating penetration in bamboo or wood makes this product effective against fungi, bacteria and insects.
Ammoniac and copper components are highly and eco-toxic non-degradable. They therefore pose problems in end of life of the product.
Due to these toxins, it is advised that not to burn tanalised products, since arsenic (which is a poison) is immediately released into the ambient atmosphere.
Since the 1990s, this product is prohibited gradually increasing number of countries and a growing number of uses.
Unfortunately, these products are still widely used in some bamboo factories without much consideration.
Treatment with Boric acid / Borax
The preservative used is a mixture of boric acid and borax which result in the formation of disodium octaborate, which is easily soluble in water. Boron salts are effective against borers, termites and fungi (except soft rot fungi), and is widely recognized to be environmentally acceptable and safe for the mammals.
These boron salts are dissolved in water. After treatment, the water evaporates leaving the salts inside the bamboo. Boron salt is non-fixing type, that is, the preservative is leachable. Therefore this process is recommended for bamboo culms that would not be exposed to water or rain.
Borax/boric acid seem to be non toxic to the environment, but is highly saline, and little is known environmental toxicity.
However, as it hasafungicideandinsecticideaction thatsuggestsit would not beenvironmentally neutralin caseofmajor pollution.
It is mildly toxic to humans. Simple exposure can cause respiratory and skin irritation; ingestion may cause gastrointestinal distress including nausea, persistent vomiting, abdominal pain, and diarrhea.
There are various way methods of treatment of bamboo.
Bamboo could be impregnated under pressure in autoclave or by boiling.
Bamboo could be soak in a solution in an open basin for several days (for slats) until one week if bamboo culms.
Or by using the “boucherie” method.
However, in all cases, borax/boric acid diffuse better into bamboo when bamboo is moist i.e. in the green condition.
The products made with treated bamboo with borax are not toxic. However treated bamboo must not be burned, as the gases of such a fire are toxic.
There is a debate either the boric acid / borax is toxic or not.
Boric acid / borax has low toxicity to humans through ingestion or inhalation. Median lethal dose (LD50) rating of 2,660 mg/kg body mass for man. Boric acid is poisonous if taken internally or inhaled in large quantities. It is generally considered to be not much more toxic than table salt. Some ethnic groups use it however as a food additive. However in some countries it is requested to farmers and restaurateurs not to use it because of unacceptable risk to consumer health.
In France, the boron content should not exceed 1 milligram per litre according to health standard for drinking water.
At high concentrations it is irritating to eyes, skin and respiratory tract where short exposure but may have effects on the kidney in cases of prolonged or repeated exposure.
The European Community decided to amend its classification as repro-toxic category 2 and to apply the risk phrases R60 (may impair fertility) and R61 (may cause harm to the unborn child).
Therefore, if it is said that borax and boric acid is already a more environmentally friendly as well as an efficient way to preserve bamboo, it is sure that it should be used carefully by operators with safety precaution.
Other alternatives methods:
Treatment of bamboo with limewater
What is Lime?
Lime has been known for centuries in the sector of buildings. After several decades when it fell into disuse, lime now finds again a new interest particularly in connection with renovation of old buildings.
Lime is a 100% natural since it consists only of stones fired at very high temperatures.
Strictly, it is an oxide of calciumwith varying oxide magnesium but the common name of lime can encompass various chemical states of this product.
The quicklime is the direct product of pyrolysis of limestone, mainly of calcium oxide (CaO).
The lime or slaked lime is obtained by the reaction of quicklime with water. It consists mainly of calcium hydroxide (Ca(OH)2).
Other forms of lime have common applications in agriculture and gardening, including dolomic lime containing magnesium and hydrated lime
What are the properties of lime?
- Natural product
- Healthy and Green
- Protection against insects - Insect Repellent
- Good thermal and sound insulation
- Anti-humidity excellent adaptation to changes in temperature and freezing
- Apply to walls: Great diffusing capacity (let the walls breathe)
- An excellent fire retardant.
In terms of ecology, the lime does not contain any product of petroleum chemistry. Lime residues can even be composted.
Healthily, lime contains no formaldehyde or VOCs and no other allergen product. With its antistatic properties, the amount of dust is minimized. Moreover it is naturally antifungal and is ideal for wet rooms. Lime is recommended for people suffering from allergies, from various sensitivities and, of course, for anyone concerned about his health.
Given these many properties of lime, and aiming to provide a 100% eco-friendly and non-toxic treatment for our bamboo, Chalet & Bamboo has developed a unique method of treatment with “lime water”.
How is the water lime treatment?
To prepare lime water, we mix the lime (slaked lime) with water. It is sparsely soluble, it is necessary to stir the mixture for some time. This step results in a white solution called milk of lime, which is a suspension of calcium hydroxide particles in water.
To eliminate the unsolved lime in suspension, we proceed to a decantation of the milk of lime for 24 hours. As a result we obtain the lime water, a clear solution.
Lime water is the common name for saturated calcium hydroxide solution (Ca (OH) 2)
In contact of carbon dioxide (CO2) it will form calcium carbonate (CaCO3), which can be seen as a white film on the surface of the lime water.
Once limewater ready, it is transferred by gravity into the basin where we placed the bamboo to be treated. Bamboos are impregnated with lime water by soaking for one week.
As with borax, it is important to perform this treatment on freshly cut bamboo. Indeed, unlike wood, bamboo undergoes anatomical changes and begins to shrink once it begins to lose water.
Sap in the vessels is precipitated, clogging the openings to the adjacent tissues. This reduces the treatability of bamboo and therefore the diffusion of preservative agents in the cells of bamboo.
Treatment in boiling linseed oil / oleo-thermal process
The culms or slats of bamboo are soaked in linseed oil heated to between 100 and 120 ° C.
The treatment of bamboo by oleo-thermal process is to our knowledge not developed mainly due to the excessive cost of energy to boil the oil in large basins.
The principle of the process is to heat the bamboo in an autoclave at a temperature high enough (for bamboo between 150 and 200 ° C), in anoxic condition and to regularly inject steam to avoid the bamboo to ignite. Bamboo is "cooked" in some way and stabilized while remaining solid. Its ability to absorb water is reduced by half.
The technique thermo-treatment of bamboo is an alternative to preservative treatment with use of insecticides and chemicals. However, heating the bamboo at high temperatures makes it stable and virtually rot-proof. It thus makes naturally resistant to borers, termites, fungi and moisture.
Bamboo products treated by this method can also be used as a structural element of a building. But bamboo from thermo-treated tends to reduce strength and flexibility, and their implementation in structure requires special precautions (such as use of larger section).
They are also ideal for flooring, decks, exterior, siding etc.
The bamboo processing under high temperatures is to our knowledge not yet developed. Chalet & Bamboo seriously considering this method of treatment but requires a significant investment.