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 specie, so be careful when you try this at home!
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.
I had a Japanese scoutmaster in the boyscouts. Making bamboo joints goes notably faster with hand tools.
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.
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.
I think that building with round bamboo is only suitable for the very poor, or the very rich... It takes too long to do it right, not to mention the waste from constantly trying to make the bamboo joints acceptable to 'high end aesthetics', or it looks like crap... I use a stationary motor with a tapered grinding stone, when I have to do it, but the dust is noxious, and it still takes too long...
My solution has been to make the rough joint bearing points as close as possible, and to use wood plugs as you do, but to make the bamboo joint pleasing to the eye, I just use spray foam (I know, that's not too eco appropriate) which stabilizes and fills the gaps, then trim it with a sharp razor, and paint it to match. It comes out looking like your pictures, and stops bugs from attacking the end cuts, and takes a fraction of the time to do...
I also use wine bottles foamed into the ends of bamboo poles for bearing on the ground, or connecting two bamboo poles into one longer one. Sometimes I put a few LEDs in the ends on the ground to make a cool way to keep from stubbing your toes in the dark...