Intro: Bamboo Joints: Duct Tape and Wire
It can be difficult to join bamboo together into structures. There are many materials that can be used, but they all tend to be rather expensive and time consuming compared to the few nails that would be required to join two sticks of wood. Professionals who work with bamboo often manufacture extremely expensive custom joint fittings, or use relatively expensive and short-lived rubber bands or zip ties to make joints.
Here, I will describe a somewhat cheaper method of joining bamboo with duct tape and galvanized wire. This is a comparatively low-quality, low-performing way to join bamboo. I would not recommend using this method as is, but with better tape and more careful wire wrapping, it would perhaps be a decent way to join bamboo in certain situations. I will explore cheaper and more durable ways of joining bamboo in future instructables.
1.87" wide "Duct" tape is roughly 4 cents per foot. Galvanized steel or aluminum wire is somewhere in the range of 3-4 cents per foot. Each joint will use ~2 cents in duct tape and 6-8 cents in wire. If you can find really great tape and save on wire, that would be ideal, but here today, we are using the tape as a temporary adhesive with limited service life in an exterior application, mostly to pad the joint so that the wire lashing won't slide loosely around the bamboo.
Step 1: Materials List; Cut Bamboo to Size
You will need:
- bamboo canes, 0.5" - 2" diameter
- roll of duct tape
- spool of galvanized wire (14ga?)
- wood saw
- wire cutter
Gather your tools and bamboo. Freshly cut (green) or dried bamboo are both easy to cut in small diameters, though if you've never worked with green bamboo and a sharp machete, it's usually much faster than working with dry canes. Cut your canes to size.
Step 2: Prepare Tape and Wrap Joints
Duct tape is usually just under 2" wide. Pull off a 6" length, and then divide in half lengthwise. Attached the two pieces end to end to get a roughly 12" strip. Wrap this strip around and between the two or more canes that you are joining.
Step 3: Cut Wire and Wrap the Joint With It
The joint is held together somewhat loosely by the duct tape. Bamboo has a waxy surface which will prevent the duct tape from sticking long term, though duct tape applied to unfinished wood will not yield a particularly strong bond either. Wrap the taped joint with galvanized wire. Start with several half hitches or a clove hitch, or twist together the free ends of the wire to make a loop and make a girth hitch; use a cow hitch; or twist a free end back onto the standing part as in image #3 -- the beauty of stiff wire. Jewellers may know of a very conservative way to do this wire work -- I don't, and require at least 18" of wire to make this tripod joint. The duct tape provides a softer, squishier surface for the wire to grasp -- wire directly on waxy bamboo will tend to slide around loosely.
Step 4: Drill a Hole to Retain the Wire
You don't have to do this, but drilling holes for the wire can make the joint stronger. Use a small drill bit or reamer (like on the pictured Swiss Army knife) and bore out a hole near a node in the bamboo cane. If you try to puncture the bamboo with an awl, nail, or screw, it will usually split -- thus the need to pre-drill. If you thread wire through a hole that isn't near a node, it may cut into the internode cane as you tighten up the wire and simply split the cane like a knife. The node provides a crossmember in the cane structure that will prevent splits from propagating.
Step 5: Final Product
I've used this technique to make other structures, but never documented it. I made this tetrahedron simply to demonstrate the method. This object can hold ~80lbs of weight on its peak, and the primary failure modes are: canes bend and shatter, duct tape shears off of bamboo surface and unravels, canes slide past and through wire wrappings. Using 2 to 5 times as much wire and tape would considerably improve the strength of these joints, but be rather expensive given the low outdoor durability of the tape adhesive. Duct tape that cannot be split by hand but which contains threads on par with sewing thread or dental floss would greatly improve the strength of this method.
Making geometric wireframes with bamboo, painting everything white, covering with rice paper or plastic, and putting low-temp LED lights inside would be one useful thing to do -- "hanging lanterns" -- with this method.
Step 6: Another Use -- Repairing Pop-up Canopy Frame
I had several broken metal-frame pop-up "event" canopies on hand. They are no longer useful for setting up and breaking down quickly, but by replacing broken parts with bamboo and these tape-wire joints, I was able to set up a 10'x10'x10' canopy as a medium-term outdoor storage shed covered in greenhouse plastic. It's rather ugly -- using materials at hand to do something which I expect to last 6-12 months, until a more permanent solution presents itself.
Step 7: Final Thoughts
Some incremental improvements to this method are clear to me. The galvanized wire can be replaced with fishing line (monofilament) and crimp ends (beading crimp tubes). The duct tape could be substantially stronger (fabric weave that requires scissors to cut) and rated for multi-year weather exposure. Beyond that, I will explore several other techniques in the near future: wrapping with wheatpaste-saturated fabric and then wire; wrapping with cement/acrylic fabric and yarn; perhaps using Liquid Nails and wire or yarn lashing.
The bamboo I work with is "yellow groove" -- phyllostachys aureosulcata 'alata'. It has a waxy coating that prevents good glue/epoxy adhesion (it can be torched and wiped/scraped off to some degree) and which hosts a black sooty fungus when untreated and left outdoors. The canes are only roughly circular in profile, with relatively thin walls that can't be pared down too much before compromising the strength of the whole pole, and which share very minimal surface contact when butted together. They split nicely into quarters with the right tool, but not with a simple knife or froe; regardless, split 2" canes are not useful as structural members. This bamboo is beautiful to grow and be around generally, but a coppice of sweet chestnut and willow would probably be more useful in a northern climate.