Building with bamboo is fun, cheap and easy. Bamboo grows faster than anything on earth, with a tensile strength comparable to steel. But unlike steel, it can rot, crack and grow mold. That is, if you’re not careful. So is it necessary to treat or season your bamboo before trying to build with it? And if so, what is the best way to treat bamboo for building?
In order to minimize the cracking and decay of your bamboo poles, and to maximize the life of your bamboo structure, it is highly recommended that you treat them before building. You can treat bamboo through a chemical process, which primarily uses borax and synthetic wood sealers. Or you can cure your bamboo poles by natural methods, involving heat or saltwater. Without proper seasoning of the bamboo, the material is vulnerable to fungus and insects. Also, the poles often crack because of fluctuations in temperature and humidity that can occur seasonally or in the process of international shipping.
In the following article, we’ll look at the different treatment options for your bamboo poles, with or without chemicals. We’ll also discuss some other precautions you can take to preserve the wood and prevent cracking. It’s also important to select the right variety of bamboo, whether you are growing it yourself, or purchasing it either locally or from overseas.
Why you should treat your bamboo
Bamboo is an amazingly strong and resilient material, but like any other organic matter, it can be susceptible to the forces of nature. Once harvested, it is important to dry and cure the bamboo poles properly. Left untreated, bamboo poles can eventually split and decay. They might also fall victim to other living things, including mold, fungus and boring insects, which can nibble away at the dry wood the same way that termites do.
Depending on the method used, the treatment can provide short term or long term protection for your bamboo. If you’re using naturally techniques, you can count on short to medium term protection. If you’re working with chemicals, the solvents used to cure the bamboo can be classified as either fixing or non-fixing. Fixing preservatives are basically permanent, and generally involve toxic chemicals, such as zinc chrome and copper chrome arsenic. Non-fixing preservatives only provide temporary protection. This is a less toxic method, mostly using boron (or borax), but it will leach out of the bamboo when exposed to rain. So it’s really not adequate for outdoor use.
The first thing to do to preserve and protect your bamboo for building purposes, is to dry it properly. Green bamboo should never be used for building. Fresh bamboo is more attractive to pests and insects, and more vulnerable to mold and fungus. Also, as the wood dries, it can shrink by about 10-15% in diameter, and it also becomes more rigid. Once these process is complete, you can build with it safely and securely.
By far the most popular way to dry bamboo is simply in the open air. This will normally take about two or three months, depending on the climate and the size of the bamboo.
The most important feature you need when air drying is good ventilation. Air circulation is critical, but the bamboo also needs to be covered, sheltered from the rain the direct sunlight. A barn or an extra garage is ideal. If you have to dry it outdoors, you can use a tarp, but find a way to prop it up in order to maintain good air flow.
Use some kind of rack to keep the bamboo off of the ground, and then you can just stack them together. If you have a great quantity of bamboo poles to dry, you can stack them in alternating directions to form a kind of grid. Don’t stack them too high, as they could crack under the weight and pressure. It’s also a good idea to rotate the poles every couple weeks to ensure even drying and to avoid bending and curving.
While trying to maintain a good air flow, also try to avoid dramatic changes in temperature or humidity. Keep an eye on the bamboo, and if you see one getting moldy, promptly remove it in order to prevent further contamination.
Kiln drying is another method sometimes used, but it is not generally recommended. This method leads to a higher risk of cracking. It’s a good system for drying bamboo that’s already been split into slats.
Curing and treating bamboo with natural methods
After the bamboo is dry, and sometimes even before, it’s important to treat the bamboo in some way to protect it from the elements. There are a variety of natural ways to do this.
This is perhaps the most effective of all methods for treating your bamboo and protecting it from insects, mold and the elements. The process uses the natural resins from within the bamboo to protect the poles. And the only thing you need for heat treating bamboo is an open flame, some heavy gloves and some rags. (Maybe keep a fire extinguisher close by, just in case.)
In my opinion, this is best done over a fire pit, but some people prefer to use a blow torch. You can also do it before the bamboo is completely dried.
The trick is to hold the bamboo in the flame until you just begin to see a little shine. The shine is from the natural resin released form the bamboo. When you see that, pull the bamboo away from the flame, and carefully (with heavy, leather gloves), rub the bamboo down with some old rags. As you rub the natural oils back into the bamboo, it takes on a natural, beautiful luster.
By this process, the bamboo really seals itself. As the resins release and are rubbed back into the surface, the bamboo takes on a protective coating that will ward off bugs, mold and fungus. And it looks incredible. If you’re not careful, you may end up with some brown spots where it got too hot. On the other hand, you may find that these leopard spots make the bamboo even more attractive.
A traditional method, still widely used, especially in Asia, is to soak the poles in salt water. This is roughly equivalent to pickling your bamboo, removing the sugars, preserving it, and making it less appealing to pests. Afterwards, they dry the bamboo in the sun for two to three months.
Alternatively, you can thoroughly air dry your bamboo poles first, and then soak them in the sea for two months. Many consider this the easiest and most effective method, even if it’s not the fastest. The bamboo can readily absorb the salt and naturally seal the bamboo for many decades.
Sealing the ends
In order to prevent, or at least reduce cracking, many bamboo builders will seal the ends of the bamboo poles, where they are most likely to crack. This prevents the rapid loss of moisture which naturally happens at the ends of the bamboo, and can be done with beeswax, paint or other products.
Another technique to prevent culms from cracking is to drill small air holes. This lets the air out of the hollow internode segments and prevents the pressure from building up in case the bamboo gets too hot, either in storage or in transit. Depending how you intend to use the bamboo, this method may or may not be desirable. But the holes can be made very small and will not affect the bamboo’s structural strength.
Treating bamboo with non-toxic chemicals
The most popular method for curing bamboo is with the use of boron-based insecticides like borax. Because they are based on minerals, these products are non-toxic and pose no serious environmental hazards. You can apply borax to freshly harvested bamboo as well as to bamboo furniture and building materials that are already assembled and in use. This provides the most effective protection against all kinds of insect infestation. It’s also useful and effective against mold and fungi.
A pre-mixed powder blend of boric acid and borax, in a 1:1.5 ratio, is available for purchase, and known as disodium octaborate tetrahydrate. This odorless, white substance is non flammable, with a relatively low level of toxicity when exposed to the skin or (accidentally) consumed orally. The product is commercially available as Tim-Bor or Solu-Bor.
Easy to use, simply dissolve the powder in water and apply it to the bamboo with a brush, a spray bottle, or by submerging the bamboo in the chemical solution.
Treating bamboo with toxic chemicals
A range of more potent and toxic chemicals can also be used to cure and preserve bamboo. Although environmentally dubious, these methods can provide protection for up to 50 years. Options include heavy metal compounds like Copper Chrome Arsenic, Copper Chrome Boron, Copper Chrome Acetic, and Zinc Chrome.
While said to be effective, I shy away from these toxic treatments. One of my primary reasons for using bamboo as a building material is its sustainability and natural appeal. And the use of these toxic chemicals detracts from those benefits.
Creosote is another option, somewhat toxic but widely used on telephone poles and railroad ties. For outdoor use only, the oily substance provides protection against water, insects and fungus. It’s most useful around the base of a structure, in places where the bamboo poles come in contact with the wet ground.
Superior bamboo varieties for building purposes
The most popular bamboos for building purposes are timber bamboos, those with the greatest height and the thickest culms.
- Phyllostachys edulis, or Moso bamboo, is very widely used in China for all manner of construction. A temperate, running species, Moso can also grow in the US, but won’t get as big as it does in its natural habitat. Generally it grows larger in warmer climates.
- Guadua is a genus of giant, clumping bamboos from Central and South America. If you’ve got a large project underway, and you’re willing to bring some bamboo from overseas, Guadua angustifolia is an excellent choice.
- Chusquea is another genus of neo-tropical clumping bamboo. It’s especially interesting for building because most species have solid (or nearly solid) rather than hollow culms, which means that cracking is hardly an issue. Chusquea gigantea is one of the more desirable species.
If you found this article about treating and seasoning bamboo helpful, please consider sharing it with your friends and subscribing to our blog. Chances are, you’ll also enjoy some of these popular posts:
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FEATURED PHOTO: An assortment of bamboo poles in various condition (Unsplash)