Making a Bamboo Fish Mouth Joint

This video shows how to make a clean fish mouth joint using only a drill and a hole saw. It’s a simple step-by-step process that takes less than a minute to complete. Perfect if you want a fast and accurate fit. (The video is in Spanish, but the steps should be pretty self-explanatory.)

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.

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⭐ Best Answer:

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. Don’t 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!

Bamboo Architecture Unboxed

By Stamm, Jorg, Vahanvati, Munir