Bamboo is one of the most durable, resilient types of plants grown worldwide. It is fast-growing and can flourish in otherwise challenging growing conditions. But does bamboo last once it’s cut down and used as a building material?
When harvesting bamboo for outdoor usage, it’s important to treat it first. This process not only extends the life of the bamboo poles themselves, but also buffs their resilience against pests, fungi, and the elements, including sun, rain, and wind. There are various methods to treat your bamboo, but almost all involve: soaking with preservatives, air drying, and sealing.
With the proper treatment and maintenance, your bamboo could last outdoors for decades. That said, some treatment methods are more effective than others, and some chemical preservatives are best avoided with bamboo that might come into contact with food. We’ll look at the various treatments you can use on bamboo and ways to help increase the life of your bamboo materials.
Why does bamboo need to be treated for outdoor use?
Due to the tree-like appearance of bamboo plants, it’s easy to forget that bamboo “wood” doesn’t have the same properties as true wood. Remember, bamboo is a grass, and its culms are full of starch, which is highly attractive to pests and fungi. As such, bamboo culms continue to be susceptible to pests and fungal growth until they’re treated.
Without any treatment, bamboo harvested for outdoor use will last about two years before it loses its strength and durability. By contrast, while it might take some time and effort, treating the bamboo first will allow it to last for many more years.
Depending on how you want to use your bamboo outdoors – whether for building a structure, a fence, or furniture – you’ll likely want to see it last longer than two years. This is why drying and treating the culms is so important. Treatment will help protect the bamboo from pests and fungal spores and provide reasonable protection from the elements.
Is bamboo easy to treat?
Treating bamboo is not hard, but it also isn’t as straightforward as one might hope. The structure of bamboo is largely to blame. The outer layer of bamboo is mostly tough fiber, while the inside is mostly hollow. The culm walls, while tough on the outside, are composed largely of starch and need to be treated to prevent serious damage from pests or fungi.
There is also some evidence to suggest that different bamboo species are better suited for outdoor use than others. Bamboo species used for timber are typically taller and stronger, though it’s not clear whether that makes them last longer outdoors than others or not.
Additionally, whether round bamboo poles are used whole or split can also affect how long they last in outdoor construction. In any case, all types of bamboo can be treated with the methods explored below.
Treating bamboo for outdoor use
There are various ways to effectively treat bamboo material for outdoor use, including chemical or natural methods. Natural treatment is sometimes referred to as curing, while treating usually implies the use of a chemical preservative. We will mostly focus on the latter.
Either way, the process of getting bamboo ready for outdoor use typically encompasses three steps:
- Soaking/treating bamboo with chemical or natural preservatives
- Drying bamboo
- Sealing bamboo
1. Step: Soaking bamboo
Soaking your bamboo after it’s harvested serves a couple of purposes. The first is to ensure that the bamboo dries evenly. Bamboo can easily split during the drying process, which could render it useless depending on the intended use. Soaking your bamboo will distribute moisture evenly through the poles, ensuring that they will dry without splitting.
The second purpose of soaking bamboo is that it allows chemical preservatives to be absorbed into the bamboo. Most bamboo preservatives are types of salts that the culms will absorb along with the water. As the bamboo dries, the water will evaporate but the salts will remain in the culms. You can think of it like you’re pickling bamboo!
To soak your bamboo, you’ll want to completely submerge the poles or splits in the preservative solution. You can make small holes in the nodes to ensure that the chemicals are absorbed into the inner layer of the culms. Since bamboo tends to float, use weighted panels or rocks to keep the poles submerged. Allow your bamboo poles to soak for at least a few days but up to 12 weeks.
Types of bamboo preservatives to use during soaking
There are a number of different preservatives that can be added to the water in which the bamboo is soaked in. These are sometimes referred to as either fixing or non-fixing depending on how the chemicals interact with the bamboo.
- Non-fixing preservatives are less toxic, but have the potential to “leak” out when the bamboo gets wet
- Fixing preservatives are more toxic but offer permanent protection.
However, with proper sealing (the final step) both kinds of preservatives can be effective at preventing damage from fungi, borers, and termites. The most popular options include the following:
Boric acid, borax, or boron
Boric acid is a chemical that is commonly available as the product Borax, though it can also be bought separately. Regardless of the name, the chemical is a compound of boron, hydrogen, and oxygen, and has effective, non-toxic pesticidal properties that have made it a popular choice for bamboo treatment.
To use boric acid in bamboo treatment, make a solution of boric acid to water with a 2.5% concentration. Of note is that this treatment is non-fixing and therefore has the potential to leach out when the bamboo gets wet, so it’s recommended to use this for bamboo that will be under cover. However, sealing the bamboo can help trap the treatment inside.
CCA: Chromated Copper Arsenate
Chromated Copper Arsenate has been considered a highly effective wood preservative, particularly due to the effect of copper against fungi and arsenic against insect invasion.
The efficacy of the fixation of CCA to bamboo remains unclear. Some insist that it is a fixed preservative. At the same time, a study on bamboo water pipes found traces of arsenic, copper, and chromium in the drinking water. These concentrations were high enough that it was deemed inadmissible by the World Health Organization. For this reason, we recommend using CCA only on bamboo that will not come into contact with food or drinking water.
CCB: Copper Chrome Boron
Copper Chrome Boron, while considered slightly less fixed than the CCA formula due to the boron component, is a safer alternative to CCA. This treatment formula consists of boric acid, copper sulfate, and sodium dichromate with a ratio of 1.5:3:4.
If you use Copper Chrome Boron for outdoor use, you’ll want to increase the concentration by 8-10% for long-lasting results.
One of the benefits of treating bamboo for outdoor use with Zinc Chrome is that the zinc chloride helps decrease moisture absorption in bamboo since it is hygroscopic. This can give your bamboo a “wet” look during the rainy season.
Zinc Chrome consists of Zinc chloride and sodium dichromate with a ratio of 1:1 at approximately 10% concentration for an effective bamboo preservative.
Copper Chrome Acetic
Copper Chrome Acetic is another fixing treatment for outdoor bamboo that is lesser known but still also considered an effective, yet toxic chemical treatment. This treatment contains copper sulfate, sodium dichromate, and acetic acid at a ratio of 5.6:5.6:0.25.
Creosote is a preservative intended for outdoor use only that is often used on telephone poles or other wood building materials to protect against water, fungus, and insects. It’s best used in areas that come in contact with the ground, where water damage is most likely to occur.
Creosote is considered a probable carcinogen, so precautions and protections should be taken to reduce contact. It also emits a foul odor and should only be used for exterior use.
2. Step: Air drying
Once your bamboo has been treated, air drying your bamboo is very important. The treatments listed above are usually added to water where the bamboo is submerged. Air drying allows the solvents to evaporate from the bamboo, leaving behind the fixed salts.
When air drying your bamboo, keeping it protected from the elements and off the ground is essential. Ideally, you’ll want your bamboo stacked vertically for efficient drying, but if you don’t have the space, you can stack your bamboo horizontally, alternating directions with each layer. The air drying process can take 2-3 months, although environmental conditions can impact the air drying time.
3. Step: Sealing bamboo
Once the bamboo is completely dry, you can add a sealant to protect the bamboo against damaging UV rays and rain. This is especially important when using the treated bamboo structurally, such as for buildings or fences that are constantly exposed to the elements.
Most wood sealants contain oils, though some are water-based. Should you want to change or intensify the color of the bamboo culms, you can choose a sealant with added pigment (also referred to as a stain).
Before sealing your bamboo, clean off any accumulated dust or dirt. Use a brush to apply the sealant to the entire culm, allowing it to dry according to instructions before using the bamboo as desired.
Types of bamboo sealants
There are several types of sealants out there that will work on bamboo for outdoor use.
Boiled linseed oil is a natural oil derived from the flax plant, and is effective when it comes to protecting your outdoor bamboo from the elements. This will keep the natural color of the bamboo.
Varnish is another practical approach, which is a solvent of resins, oils, and solvents. You can get transparent varnish to keep the natural look or add a stain to give your craft a different color.
Other ways to help your bamboo last longer
Placement and maintenance are key to helping your bamboo last longer. It’s best to keep your bamboo off the ground, which limits prolonged moisture contact. Though not always possible, sheltering and limiting your bamboo’s exposure to extreme elements like sunlight, rain, wind, and snow will also help your bamboo last longer outdoors.
It’s also important to regularly reseal your outdoor bamboo, every 2-3 years for best results. You can do this by first cleaning the bamboo, allowing the bamboo to fully air dry, and then finally applying the sealant. The last thing you want to do is reapply sealant to wet bamboo, which will lock in that moisture and facilitate rot!
FAQ about treating bamboo for outdoor use
Are there sustainable ways to treat and preserve bamboo?
Due to its fast growth rate, bamboo is a very sustainable building material, but it doesn’t last very long without treatment. Currently, the most popular commercial methods involve chemical treatment, though there are options to preserve bamboo with more environmentally friendly methods.
For example, researchers in the Philippines are giving bamboo culms a “hot oil bath” as a means of preservation, which has promising results. Hopefully, in the future, these types of methods and others will become more common so we can have durable bamboo without adverse environmental impacts.
Can bamboo furniture be used outdoors?
If treated and maintained properly, bamboo furniture can be used outdoors. Shelter your bamboo furniture from prolonged rain and moisture as much as possible. Clean your bamboo with a damp cloth to prevent dust and dirt from accumulating in harder-to-reach spots. Make sure to reseal the furniture with a wood varnish or oil regularly to make it last as long as possible.
Do you need to use chemical preservatives to treat bamboo?
For more short-term preservation, you can bypass chemical preservatives and simply soak your bamboo in salt water, air dry it for outdoor use, and seal it. While untreated bamboo may not last as long, you can still get at least several years out of your outdoor bamboo without using chemical preservatives as treatment.