The GUADUA bamboo we are treating is one of the top ten construction bamboos in the world. It is used extensively in Columbia. Costa Rica has built many homes, hotels, walking and driving bridges with 100 ft spans, and other structures using this bamboo. Stronger than steel for its weight, and stronger than a solid wood pole of the same diameter, Guadua bamboo is a viable replacement for structural steel. More fire resistant (before adding the boron, which is also a fire retardant) than wood or steel. Note: Steel fails before wood under lower heat conditions.
Why treat Bamboo?
Bamboo is an interesting plant. The new growth can grow up to a meter per day and it has no leaves. It is being fed by the stored sugars (starches) in the older plants till it can produce its own. These starches are very desirable to insects. Treatment is to either remove these starches or make them unpalatable to the insects. This can be done by soaking them, smoking them, or treating them with a variety of chemicals, some quite toxic.
There are a two philosophies on this. One is to cut the bamboo on a lunar and tide cycle. This is done with trees and seems to have some evidence that it works. But Oscar Hidalgo in Columbia points out that Bamboo is a grass, not a tree, and his experience shows that harvesting on the lunar/tide cycle does not work for bamboo. Here in Panama there are stories of bamboo cut in this way lasting for years. There are more stories of bamboo lasting only a few years when cut in this way. So it is important to treat the bamboo if you want to assure the structure is to last more than a few years, and not waste a valuable resource (and the cost of labor to remove & replace it). If the bamboo is treated, the timing of the lunar/tide cycle becomes mute. It can be harvested at any time.
Only Mature culms over three years old are harvested for structural material.
There are several ways to treat bamboo. Some will not work on all species of bamboos. The only two I thought were commercial viable were both treated under pressure, but using very different approaches. One is to use the same pressure treatment system used in treating wood. Running the material under a sequence of vacuum and pressure with a 2% solution of the same chemical we use for the other system. This type of system is very capital intensive. Building one of these requires a central location for treatment and storage, and drying. It allows for a shorter treatment time, and allows larger volumes to be treated at once (depending on vessel size). Capital investment is the drawback to this system. You have to sell a lot of bamboo to make this cost effective. We are concentrating on local, not international markets at this time.
Soaking bamboo in a solution for weeks does not give the same penetration, and is slow and for production purposes as a business, not cost effective.
There is a Vertical Soak Method that is also slow, and penetration very much depends on the species!
The Boucherie method
We have chosen a tried and true system called the modified Boucherie method. This was invented about 180 years ago for treating trees. It has been modified to treat bamboo, a grass. Bamboo has a very different vascular system than a tree. The vascular system is spread out throughout the entire culm wall, while a tree has a cambium layer just below the bark. This method is well suited to treating bamboo. Distribution is throughout the entire thickness of the wall, not just the outside layers.
This method uses freshly cut bamboos that are still green. The 10-13% Boron solution is pressurized from the base of the culm and forces the fluids thru the vascular bundles. A dye is put into the solution so we know when the culm has been fully penetrated.
We are able to treat 20 foot culms at this time. We have achieved 30PSI pressures, which to our knowledge is unheard of in the industry. We have manufactured all our own treatment equipment and connections to achieve these pressures. Treatment times to achieve verifiable full culm penetration vary from an hour and a half, to 5 hours or more. Both of those extremes are rare, and most are in the 2-3 hour range.
The chemical we use is called by its long name, disodium octaborate tetrahydrate Na2 B8 o13 + 4H2O. Basically it is eight boron atoms linked to two sodium atoms with oxygen and water. Commercially, it goes by the names Timbor and Polybor. It has a PH of 7 and is used as a foliar spray in organic farming.It is also a metal preservative, so it will not corrode fasteners. Boron is toxic to insects, and a mild fungicide, but pretty nontoxic to mammals. This form of boron has more boron atoms per molecule than other forms, ie Borax or Boric Acid. Boron products are also used as fire retardants. We are able to recapture and recycle virtually all our product. This product is used by pest professionals for treating wood boring pests in homes by more continence termite inspection companies in the US. We use this product in a 10% solution, which is dependent on ambient water temperature.
This chemical can also be mixed with Propylene Glycol (the much less toxic form of the antifreeze ethylene glycol) to make a product that is better absorbed for use on wood surfaces. Propylene Glycol is used in heat exchangers used in food processing and home solar drinking water supplies as a heat transfer and freeze protection fluid, due to its lack of toxicity. This can be used as a surface coating. It is colorless and odorless. Our plant is potable, so we can treat on site, if the situation allows. This allows us to dry on site and reduce transportation costs. These savings can be passed onto the consumer.
Drying takes about six weeks depending upon weather and humidity. Bamboo must be fully dry before use, especially if you are filling sections with cement. After drying, the bamboos can be cleaned if desired and sanded and sealed. Bamboos treated in this way are meant to be used under roof. If they get wet for extended periods, they should be sealed from rain. The Boron chemical is water soluble, so long term exposure to rain will eventually dissolve the chemical making the culm susceptible to rot. This will take much more time than untreated bamboo, but given enough rain and time, it will happen. Sealants can be varnish, lacquer, latex, or oil paints.
These culms are not meant for earth contact, though some folks have had good luck sealing them in tar or plastic prior to burying. It is typical to encase them in concrete piers as a foundation, again under roof. Strips of bamboo have been used in concrete floors and foundation in the place of steel reinforcement with some good success.