Making a Bamboo Fish Mouth Joint

This video from the Technology Institute in Costa Rica shows a basic technique in bamboo construction: the bamboo fish mouth joint. Notice the backslash of the drill in the beginning of the video. Guadua bamboo is a thick walled timber species, so be careful when you try this at home!

Comments:

Reece

Typical reliance on the modern speed tools rather than traditional tools, techniques and skills. This work requires a coping saw and appropriate rasps, not a bunch of hodge-podge reaming with hole saws on electric drills.

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Jason

I had a Japanese scoutmaster in the boyscouts. Making bamboo joints goes notably faster with hand tools.

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Harvey

A man who knows how to really use a machete can do far better, faster, simpler and certainly safer.

Notch the bamboo when green. There is very little waste and the kickback danger shown using power tools is avoided. There is nothing green about the use of power tools.

Hardwood round T's inserted into the dried and treated bamboo allows for expansion from dry to wet season.

As a designer architect I visualize in my work with bamboo it is essentially a post and beam construction.

Bamboo posts in wet locations are treated as if they were hardwood. Pilings are formula cement pours with welded (not wire tied) rebar cages with the bamboo column set into using rebar up through the column and also shooting a slurry of cement (different formula) into the base. This the same concept done to stabilize columns in earthquake/hurricane/tsunami construction. The piling with its rebar armature must be at least one meter into the ground/base with at least five inches of packed small gravel at the bottom of each piling. The ground/foundation area must be packed and left to settle at least one rainy season. The better the pilings the stronger for settling and earthquakes. A distance on center of pilings is = no more than 2.5 meters. Three smaller diameter (3-inch) bamboo columns together equal are the equivalent of 10-inch column if set correctly.

I like the idea of using a wine bottle and will experiment with same.

The Japanese perfected the used of bamboo in small footprint structures, fencing and wall/floor matting. Yet, I would not suggest using these tie and bind methods in a two story shelter in Latin America.

I also would never use a bamboo exterior roofing system in Latin America. The lifespan of a bamboo roof (covering) compared to a double coated metal roof one is about maintenance and safety.

I work in the Pacific southern zone of Costa Rica. Besides the intensity of the rainy season the sea air is a serious factor.

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Noah

I have found that forming a fish-mouth in three steps is fast and accurate. First I cut a 'V' shape to the correct width and depth with a handsaw. Then I use a curved chisel to remove the remaining bits and complete the shape. I check the fit and if there are some high spots I use a round rasp to remove them. This is fast, accurate and requires no electricity - something we rarely have here in Nepal.

"Improving" on traditional techniques is what brought us to high embodied-energy construction. It appears to be human behaviour to constantly modify/improve without consideration of consequences or necessity.

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Filling Bamboo Joints with Cement

I saw some info about creating strong bamboo joints when using Guadua in building construction, especially adding cement to the joints. I recall threaded rod and hardware being used, and possibly rebar as well. I would love to see more detailed info and/or videos about that. Perhaps there are some good videos on the site already that I have missed.

Comments

Paul Westberg

Can't remember where I saw it, but somewhere there was a video on cement filling of bamboo for added strength. The application was for attaching a ring to a pilaster. The PDF on the learning part of this site has the metal hardware demonstrated. The cement was filled into the joint by drilling a hole in the side of the pole and filling it with a mortar applicator (looks like a cake decorating tool). My question would be how long to let it cure and what problems arise from possible discoloration of the cement absorbing into the pole?

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Erik

Filling bamboo poles to reinforce the joints has shown very limited results. The problem arises from the fact that the cement mixture has water in it. So when injected in the bamboo cavity the bamboo sucks up part of the water from the mixture and the bamboo fiber swells up. When the cement or concrete sets it hardens and the bamboo dries. So it shrinks again. Pulling itself loose from the cement core and leaving a capillary opening between the bamboo and the cement. In addition to that, cement is very good at taking pressure-loads, but terrible at tensile strength (pulling). And it is heavy. So making a lightweight construction with bamboo does not seem to make much sense if you want to use heavy cement or concrete joints. Usually the motive for using cement is that it is cheap, and the builder (not being specialized in bamboo building but in general building) knows cement, but lacks the knowledge of using it in combination with bamboo.

There are better alternatives. One of them is using bamboo fiber with a matrix. A matrix is just a glue of some sort that fixes the fiber in place, mostly polymers made by chemical industry. Unfortunately good matrix-es usually do not come cheap and mostly are not very eco-friendly. But technically they are good and reliable. Basically what you do is building an exoskeleton of bamboo fiber held in place with the glue around the connection. Pretty much like you would make a cast around a leg when someone has a broken bone. The best results we had with a pre-woven strip of about 5 cm wide wrapped around the column in a cross overlapping pattern in MANY layers and then saturating it with the polymer. The best result are achieved when assuring both chemical AND mechanical bonding between the matrix and the bamboo. Mechanically is easy: roughen up the contact surface. Chemically is harder. But usually when you use a matrix that is properly absorbed by the bamboo fiber it should be ok. Keep in mind that the outside layer of the bamboo is not just hard by itself, but is hard because it contains a high level of silica. Making it more weather resistant, but also more anti-adhesive. Scraping it of before you apply the fiber and matrix might be a good idea.

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How to Join a Bamboo Pyramid?

I am using guadua as the corner posts for a pyramid. Any suggestions as to how to join these at the top would be greatly appreciated. The lengths of the posts will be 8.5m, the pyramid base 9m x 9m. The height at the apex 6.5m. We need to get the joint exactly right to ensure the energetics of the structure are correct. Suggestions as to how to raise the posts are also appreciated.

Comments

Rob Roark

I have built many pyramids and other bamboo structures, the easiest way is to cut your pieces as closely to ideal. I assume that you are using the Great Pyramid scale...

Depending upon the diameter of the poles, bend some stiff wire or cable, if you want to use tension for stability, run the cable through the entire length of the pole, and use threaded ring bolts to draw the pieces together with washers (can be made with bamboo too).

If the piece is not going to be moved a lot, just use wire angles to hold the proper angles (Duct tape will help) and spray a large amount of "Good Stuff" spray foam into the joint. Use a small bent rebar in the foam joint, and trim off the excess with a razor blade. Paint the whole piece "Bamboo Green", and the piece looks seamless!

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Mark Essert

Given the size of the structure I would start with a temporary, large diameter, center post. Cut each corner member to in a concave miter to meet the center post. (Using a 6x6 square post would be easier).

Once opposite members are leaning against the center, drill through all 3 members (opposing and center) and through the bolt. Bolts should stagger from those in the opposite direction which join the other two corner members.

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Erik

Here is my advice:

Cut two pole ends in the right angle so that they have a flat surface where they touch. Cut it about 10 cm above a node in the pole to prevent it from splitting. Find a piece of bamboo that is just oversize to fit inside the bamboo poles. Scrape off the outside layer just until you can slide it in but with a tight fit. Insert them into both ends and cut them just above the node flush with the surface you cut at the large pole end. Take a piece of strong wood large enough to cover the (oval) pole ends about 2-3 cm thick. Trim of the excess wood sticking out. Place THICK dowels in the wood sticking out on BOTH ends. Mark the holes on the bamboo pole ends and drill them to the size of the dowels. Don't drill too deep! Put a bucket load of (waterproof) glue on both ends of the wood, on the dowels, and the pole ends. (If you don't find any glue in your underpants a week later, you did not apply enough glue.) Press both ends together and keep the PRESSED together until the glue is DRY. As in fully cured.

Provide a proper foundation for the poles that protects it from ground moisture. Either a concrete foot or a steel pipe in a bedding of gravel might do the trick. Do be cheap on the foundation. Unless you want big hospital bills from collapsing roofs etc. For this size, depending on weight of cladding, expected wind loads and snowfall I would say you need AT LEAST 1 m³ for every pole.

Good luck!

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