Bamboo properties

[camhard]

Bamboo seems to be increasingly popular as a core material. I was pretty much settled on building a full bamboo core, so I got some sample vertical laminate from my wood supplier. I had a long discussion with him about all sorts of woods and their properties; even he didn't know that much about the properties of bamboo and asked me to get back to him with what I found. Online, there are claims of bamboo's extreme hardness/durability, sustainability, poppiness, strength and weight. I wanted numbers though, to compare with other woods. The first test was elasticity. Because it was so hard and apparently poppy, I expected it to be relatively close to the elasticity of my comparison maple strip. Using a flex measuring instrument and some weight, however, the bamboo turned out to be super easy to bend. It looks like the MOE is around 7000. This puts it in at about the same level as some cedar. Sugar maple has an MOE of 14100 and even eastern white pine is 9380. I was still pretty convinced that it was the way to go because it was so light. I happened to pick up two small pieces of the bamboo and some douglas fir that I was also testing in one hand. The fir felt so much lighter, even though each piece was just 21cm^3. How could this be? Bamboo was supposed to be around 50%-75% the weight of Douglas. I went straight to the scale (not a super accurate one) which told me that the fir was a full 2g lighter than the bamboo (approximately, but it's still pretty significant - that's more than 16% lighter)!

Some of my tests were more scientific than others, but even if my numbers aren't bang on to 5 significant figures, the difference was clear, even without the use of instruments, just holding and flexing the test pieces. Has anyone made and tested a pair of bamboo skis? I know there are a tonne of species that will affect the results, as well as the ply you've used, but properties should be somewhat similar throughout bamboo (I used the Phyllostachys Pubescens species, just in case you were wondering).

Anyways, any bamboo experience and knowledge would be greatly appreciated. I know there are some other threads that discuss this material, but hopefully this will turn into something with all of the available information, from environmental considerations to physical properties and special construction methods.

[G-man]

Thanks for sharing your observations. I spent much of my youth surrounded by bamboo forests and made many treehouses, carts, rafts, cages (mostly to house my annoying little brother when mom and dad weren't looking), fishing poles, etc from bamboo stalks. In it's natural tubular state, bamboo is a really strong material, but when that natural structure is altered by cutting it into thin strips, many of the original properties are diminished. As others on this site have suggested, bamboo laminate products may not be as 'green' as the suppliers of the material would like the general public to believe. It does, however, grow quite quickly and it does grow well in some parts of the U.S. If you happen to be a ski builder living in Southern California and want to use bamboo as a core material, you could grow all the bamboo you need right in your own back yard. Now, that would indeed be 'green'.

G-man

[camhard]

Thanks. Is bamboo native to So Cal? I thought in order to make it a really 'green' building material, all we would need to do is plant some bamboo here. Then, about a minute later I realized that it's not really from around here, as far as I know (I've had some bamboo shoots sprout up in my yard, but I think it's because my neighbours have some planted). Again, I'm not sure if this can be said for all species, but the stuff I've seen growing not only regrows quickly, but also spreads quickly and uncontrollably. If we started planting bamboo where it doesn't belong, there is no way we could control it and it would no doubt become a very problematic invasive species. If only a few people plant it in small quantity (as has happened already), it won't become to big of a problem, but if a bamboo farm or forrest is formed, I think this would present some very serious problems.

How about the 'snappiness' of the processed material?

[G-man]

No, bamboo is not native to So. Cal., but I lived on a ranch where the prior owner's dream was to mimic the Southeast Asian jungle. He was quite wealthy and was able to import hundreds of exotic plants. We had acres and acres of many varieties of bamboo, ranging in size from 4 to 6 inches in diameter and 30 feet tall, to plants that only grew 1/4 inch in diameter and 3 feet tall... and everything in between. We cut it down like crazy (all of us kids became pole vaulters at an early age), but it always grew back very quickly. So, even though bamboo is not native to So. Cal., it grows very well there... ever been on the Jungle Cruise at Disneyland? All of that bamboo is the real deal. Also, I recently read an article about a bike builder in Santa Cruz, Ca. who goes out behind his shop and cuts bamboo to make his bamboo bike frames. In terms of invasiveness, I don't recall it being difficult to control... urban sprawl eventually took care of our bamboo forest... and bamboo hasn't taken over Disneyland yet... at least I hope not .

In terms of using bamboo as a 'snappy' core material, it seems that your own tests have given you some reasonably useful information... the MOE is kinda low, density is kinda high. As you may know from reading other thread topics, I personally don't place a lot of emphasis on a ski's core material as it relates to a skis 'pop', 'snap', or flex. The core serves primarily as a spacer for the structural composite layers and as a damping element for resonance. Yes, with really thick cores using really dense woods, the waist of the ski will feel some effect from the core material, but who wants to lug around a ski that heavy? I'm sure that bamboo works just fine for a ski core, especially if it is grown locally, but I really doubt that it exhibits any great performance advantage over other common (and less production/transportation intense) woods. As always, I could be wrong about any of this, and, as always, eager to hear other perspectives.

G-man

[rockaukum]

At my prior residence the "neighbor" had planted bambo. I found it to be very invasive. It did spead quite quickly and was very difficult to control (keep out of our yard). I ended up digging down about 1 1/2 to 2 feet and remove all the material in order to get rid of it. I then placed a piece of flashing along the fence line (burried) in an atempt to keep it from comming back.
ra

[doughboyshredder]

I tested a full bamboo core snowboard for a week, quite a few years ago. We used full length bamboo strips in the core. The board rode real soft and smooth with an insanely consistent flex. There were no weight savings, and the cores cost more, so the idea was shelved. I would like to build another, simply because of the feel of the board, but I would make sure that the core was comprised of full length strips of bamboo, not 10" flooring laminates.

[G-man]

doughboyshredder wrote:

The board rode real soft and smooth with an insanely consistent flex.

This is just the way I describe my pine core boards. I think that the smooth ride (resonance damping) is a function of having a softer, less dense wood in the core... qualities that both pine and bamboo seem to share. The "soft" and "insanely consistent flex" are products of how the core was profiled, not what material the core was made from. Of course, soft and consistent flex also contribute to a smooth overall ride. I can certainly understand why you would want to duplicate the ride qualities of that early bamboo board... I'm just suggesting that maybe you can do it without the bamboo.

G-man

[doughboyshredder]

I would guess that you are prolly right. The reason being discussed at the time had something to do with the length of the fibers. I believe that most wood fibers are short whereas bamboo naturally grows with longer fibers. The board was built on a production shape so my comments were comparing the bamboo core to our standard core at the time, so I don't think the consistent flex (which all testers commented on) was primarily from the core profile.

[G-man]

doughboyshredder wrote:

The board was built on a production shape so my comments were comparing the bamboo core to our standard core at the time, so I don't think the consistent flex (which all testers commented on) was primarily from the core profile.

Interesting. Do you recall what type of wood you were using for your cores at that time? My general hunch has been that a core made from a really dense wood could interfere with a consistent flex due to the thickness of the wood at the waist, resulting in a flattening of the flex curve in that section. The experience you describe above provides some good information.

G-man

[doughboyshredder]

It was over 10 years ago, and I just don't remember. Locally sourced in the Pac NW.

[Easy]

I must admit that I have not read all posts in this thread in complete detail, but I have 2 remarks:

1. If you want to use bamboo as a good laminate building material (like the stuff you buy off the shelf), you need to let it grow for 5 years. The plant needs to mature that long to get the correct material properties. So it would be quite a long wait before you could build skis out of your own bamboo.

2. There are special textiles available which you can put into the ground to surround the bamboo. This stops the bamboo from spreading beyond that border.

[Mikkelsen]

camhard,
I too wanted to build with bamboo, as all the marketing hype had me convinced that it was the ideal material, being strong in both tension and compression (what is described as "poppiness"). I bought the highest grade bamboo that I could find from a respected supplier in the bamboo industry. It was 5-6yr old when cut, and natural color (the steaming process to get the carmelized color permanently softens the material).

When It arrived I compared it to ash. It was very similar in density. It could flex further without breaking (tension), (but I have never had a problem with my ash breaking in an actual ski.) However in compression (having the wood spring back to it's orriginal position) the Ash was far superior. In fact I was so disipointed, I scraped the whole idea and never built with the material since I was wanting more spring in the wood. My experience was that it would be a heavy core material for how little it was giving back, that I might as well use playdough. I think that it could be put to good use however as side-walls as it does not splinter out like wood does. You asked about "snapiness"...it is absolutly dead compared to the Ash which is almost identical in density.