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Bamboo Treatment and Preservation

Why is the treatment of bamboo required:

Bamboo is a very hardy plant with natural pest and disease resistance. Also, Bamboo contains a large amount of starch and some sugar in it which attracts fungi, mold, termites and powder-post beetles etc. So it needs to be treated in order to increase its longevity and to protect the bamboos from insects before it is used for manufacturing furniture, handicrafts etc.

An untreated bamboo is considered durable for 2 years if stored and preserved from moisture and insects it may last 4-6 years. Though actual longevity may vary depending on the species, thickness, length etc, if treated properly a bamboo or its furniture may last up to many decades.

What is Treatment:
Bamboo treatment is a process in which the starch, sugar, and moisture contents of bamboo are administered/removed thus making it resistant to termite, fungus & bugs.
There are various methods in which bamboo has been treated for years now, Traditional methods which include torching, smoking, curing, whitewashing and more modern methods which treat bamboo using various chemicals.

There are various methods for treating a bamboo. Choice of those methods would depend on various factors like:,
  1.    whether the bamboo is green or dry. 
  2.    whether Short term or Long term Protection is required.
  3.    whether it is a round bamboo or in splits or in pieces.
  4.    Is it going to be used outdoors or indoors
  5.    Is it going to be used for structural purposes /Furniture / Handicrafts etc?
  6.    The scale of Operations (A method might be viable only for small-scale/large scale operations)
  7.    Availability of resources (machinery, chemicals, time etc.)
Traditional Methods: 
These are commonly used in traditional societies of bamboo abundant areas. These are simple and cost-effective methods without the use of chemicals or any special equipment.
  1. Curing Method: The freshly cut bamboo culms along with leaves etc are stored in shade for 1-2 weeks. There is a significant loss of starch contents in bamboo culms due to the respiration in tissues and leaves. Thus it is always advisable to at least complete the curing method before using the bamboo.
  2. Smoking Treatment: The Process of Smoke treatment of bamboo goes back thousands of years. In ancient times people who lived in bamboo houses realized that the smoke from an indoor fire-pit prevented insects and other infections of bamboo, thereby increasing the age of the structure. In Japan, when old buildings are demolished the bamboo components of roof/ceiling etc. are sought after by bamboo artisans for their aged, smoked bamboo. The process of 'smoking' a bamboo is simple. Bamboo culms are placed inside a room above the fireplace and are exposed to heat and smoke for an extended period of time perhaps several weeks. The toxic agents in the smoke and heat destroy the starch in bamboo making it immune to attacks by insects and fungi.  It also blackens the culms giving it a nice texture and making smoked bamboo easily identifiable. Smoked bamboos are usually used in making bamboo structures like houses etc.
  3. White Washing treatment: This is another method of Bamboo treatment, This requires the bamboo culms to be painted with slaked lime (Calcium Hydroxide - Ca(OH)2). Up to 4 coats of whitewash are painted for better results. It is done mainly for the ornamental effects, but apart from enhancing the appearance of the culms, this method also protects the bamboo by preventing the moisture to enter the culms, as a bamboo with lesser moisture is less prone to fungal attack, it prolongs the life of bamboo.
  4. Soaking Method: Bamboos are soaked in either running water or water ponds from a few weeks to a few months to leach out the starch, sugar and other water-soluble contents. If bamboo is soaked in stagnant water (small ponds etc.) the water is changed frequently to avoid fouling.  In coastal areas bamboo is soaked in sea water. apart from leaching the starch inside the bamboo, bamboo also absorbs the salt from the sea which further helps to prevent the insect attack. This is a very cost-effective, natural, safe and environment-friendly method used in various Asian countries.
  5. Heat Treatment Method: Bamboo is exposed to heat in this method by baking or torching them. This method is very useful for straightening of bamboos. When a bamboo is exposed to heat in it rapidly reduces the moisture content of bamboo, and causes charring and decomposition of starch and sugar contents. It is very important to punch holes through all the nodes of bamboo as the air inside could cause bamboos to crack or even explode in some cases when heated. A regular blow torch or open flame of any kind could be used to heat the bamboo. The bamboo is rotated on over the flame continuously to prevent overheating. The oil and wax which draw off the bamboo is wiped with a lint free cloth before it is reabsorbed inside the bamboo. The bamboo is torched slowly section by section until bamboo loses its green color and attains a darker yellowish color. Once the complete bamboo is yellow in color it is then torched again to darken it more until it gets the desired color. Afterward, the bamboo is often rubbed with beeswax or some other kind of wood sealer to make it moisture tolerant.
Non Traditional Methods (Chemical Methods):
With time we have discovered many new treatment methods to decrease the degradation of bamboo and make them less prone to insect attack. These methods use chemicals and preservatives to ensure the long-term treatment of bamboos. These methods provide better protection than the traditional methods when exposed to adverse conditions. These treatment process either involve :
  1. Brushing Method: The preservatives are applied by brushing the outer parts of bamboo. It is suitable for small handicraft and household items. 
  2. Spraying Method: The chemicals are sprayed on the bamboo culms. Bamboos are stacked in the horizontal position on a sloping surface(to collect the draining liquid for reuse). Various industrial spraying solutions are available. It is useful for a large stack of bamboo but a small stack could also be sprayed using a backpack sprayer.
  3. Dipping Method: The culms are dipped in the preservatives momentarily (few seconds to a few minutes) in large tanks. It is more effective than spraying or brushing.
  4. Butt End Method: The freshly felled green culms along with branches and leaves are placed in upright positions in solution filled vessels. The butt end is immersed in about 25 cm of preservative solution. The solution is sucked up as the bamboo leaves and tissues transpire. The method takes 1 to 2 weeks to complete during this period the vessel is refilled to the required height as the solution level reduces. 
  5. Soaking Method: The culms/ splits/slivers are dipped in the waterborne chemicals for extended periods(1-2 weeks to a month) in large tanks. The treatment time could be reduced by increasing the concentration of the preservative in the water. The 
  6. Pressure Chamber Treatment: The culms are stored inside watertight chambers and the chemical water solution is injected into the pressure chambers thus increasing pressure. The bamboo is kept in those chambers for 7-10 days. This method is more effective and faster than the dipping methods. 
  7. Hot and Cold Bath Treatment: The bamboo is submerged in a tank of chemical solutions. The chemical is then heated up to 90 °C and after maintaining the temperature for some time it is the allowed to cool. Heating causes the cells to expand and lose moisture, and cooling causes contraction and the preservatives get absorbed in the bamboo. This method allows large quantities of bamboo to be treated in a very short period of time.
Chemicals and preservatives:
There are four main types of chemical preservatives used in bamboo treatment. They are categorized as :
  1. Natural Toxicants: Some natural materials can increase the longevity of the bamboo and preserve from insects etc. These natural plant products are not as effective as their chemical counterparts and do not provide long-term protection. Splits and slivers of bamboo are boiled with fresh leaves, fruit and stems of Giant Indian Milkweed (aka Arka / Aak / Madaar in India) to protect it against the attack of beetles and fungi.
  2. Water Borne: These are again classified into two types: Fixing types and non-fixing types. These are Water soluble chemicals formulations when applied to bamboo water eventually evaporates leaving our preservatives behind. They are of two types : 

    1. Non-Fixing Types: Which could leach through bamboo. These types are recommended for bamboo to be used indoors and in dry conditions.
      1. Boric Acid and Borax: The combination of boric acid and borax is a very effective fungicide and insecticide for bamboo treatment. These chemicals have an infinite shelf life and are a fire retardant. These are non-toxic and could be used in bamboo products which come in contact with food. The suggested ratio for this chemical is :
        Boric Acid - 1 Parts
        Borax - 1.5 Parts
        Water - 100 Parts
         Bamboo can be soaked, sprayed, brushed or injected with this chemical.
         Boric acid - Borax mixture is often used along with Sodium dichromate in the ratio of 2:2:0.5 ie.
        Boric Acid - 2 Parts
        Borax - 2 Parts
        Sodium Dichromate - 0.5 Parts
        Water - 100 Parts
      2. Copper Sulfate: Copper sulfate is an organic pesticide and fungicide which occurs naturally. It is a compound of Copper and Sulfur. It is very effective in killing bacteria, fungi, algae etc. Copper sulfate is mixed with water in a bucket and freshly cut bamboo are placed in upright position in those buckets (Butt Treatment Method). Solution naturally gets into the bamboo as the bamboo tries to get nutrients from the bottom end. Link 1: https://geneticliteracyproject.org/2017/09/08/closer-look-popular-organic-fungicide-copper-sulfate-compare-glyphosate/ Link 2: http://npic.orst.edu/factsheets/cuso4gen.html
      3. Zinc Chloride : Zinc chloride is a waterborne non-fixing type salt. It is highly acidic and highly hygroscopic. Thus giving a wet look to the treated bamboo.
      4. Sodium Penta Chloro Phenate (NaPCP): It is an effective fungicide in the prevention of molds and blue stain fungi. It is banned in various countries due to its toxicity. It warrants careful uses and not to be used for any indoor uses.
    2. Fixing types:
    3. These formulations do not leach out of bamboo and remain chemically fixed. These types require a few weeks for the process of fixation.
      1. Copper Chrome Arsenic (CCA): Copper Chrome Arsenic is a water-soluble (Fixed) type bamboo preservative. It is used for very long-term preservation. It gives effective preservation for up to 50 years. Due to the toxicity of arsenic, it is only recommended for use in exterior applications and outdoor uses. The recommended formulation is:
        Arsenic Pentoxide ( As2O5 ) = 1 Parts
        Copper Sulphate ( CuSO4 ) = 3 Parts
        Sodium dichromate ( Na2Cr2O7)
        Or
        Potassium dichromate ( K2Cr2O7 )
        = 4 Parts
      2. Copper Chrome -Boron: It is a good alternative to the above mentioned CCA but less effective and a lower degree of fixation due to the boron component. This preservative is comprised of:
        Boric Acid ( H3BO3 ) = 1.5 Parts
        Borax ( CuSO4 ) = 3 Parts
        Sodium dichromate ( Na2Cr2O7)
        Or
        Potassium dichromate ( K2Cr2O7)
        = 4 Parts
      3. Arsenic Pentoxide: Arsenic Pentoxide is an odorless toxic compound which acts as a wood preservative, insecticide, and fungicide. It is a water-soluble material and is to be used only for outdoor uses due to toxicity.
      4. Ammoniacal Copper Arsenate (ACA): It is a very effective preservative which gives very higher penetration and better protection due to the ammonia in the compound. This formulation is comprised of Copper Sulfate and Arsenic Trioxide.
  3. Oil Based:
    1. Creosote: Creosote is a dark-colored viscous liquid manufactured from the distillation of coal tar and is used as a wood preservative. It has been in use as a wood preservative since the mid-1800s. It is very commonly mixed with fuel oil in a ratio of 50:50 to create an effective preservative. The fuel oil in the mixture prevents against evaporation and leeching. It is used in pressure treatments and hot and cold treatments. Bamboo used in outdoor applications is usually treated with this preservative. Creosote is considered a probable human carcinogen. So Creosote treatment should be used strictly for outdoor uses and not in residential/indoor uses. It is a cost effective preservative against moisture, fungal and insect attack. Users may want to check the link for more details regarding creosote: https://www.epa.gov/ingredients-used-pesticide-products/creosote
  4. Organic Solvent-Based:
    1. Pentachlorophenol (PCP): It is a very popular fungicide and insecticide, its use has been banned/reduced in various countries due to its toxicity and environmental hazards. It is mainly applied to bamboo using the pressure method or by spraying/brushing/dipping/soaking etc.
    2. Trichlorophenol(TCP): It is a slightly more eco-friendly alternative to previously mentioned pentachlorophenol. It is a white to yellowish crystalline solid with a phenolic odor. It is used as a fungicide, insecticide. It is also applied to bamboo using the pressure method or by spraying/ brushing/dipping/soaking.
    3. Copper / Zinc Soaps: These came into existence due to the lack of environment-friendly organic preservatives in the market. These are commercially made solutions which are slightly more expensive than PCP or TCP but far more environment-friendly with no foul odor.
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