Tuesday, May 17, 2011


I'm not a major "hemp will save the world" campaigner, but it seems obvious this valuable material should be grown. It seems like it can be made into anything, and the products that come from it are carbon-neutral. It could also be a useful cash-crop to farmers, who could use the help.

This film was posted on Typer Cowen's blog, Marginal Revolution. He writes:

During World War II hemp made a brief comeback as an American crop due to shortages of rope-making stock from other countries. Hemp for Victory is a 1942 US Department of Agriculture film that encourages farmers to grow hemp. It opens with a discussion of the ancient history of hemp (canvas derives from cannabis) and then moves into how it is being farmed in Kentucky and other US states to help in the war effort.

The film has an interesting history. For decades the USDA and the Library of Congress denied that such a thing had ever been made but in 1976 Rastafarians delivered a copy to a reporter in Florida.

There is a building material called hempcrete, which is made from hemp hurds (shives) and lime (possibly including sand, pozzolans, or cement). Hemp ‘hurds’ are the pithy stuff inside the fibrous sheath of the stem. Separating the fiber from the hurd was one of the production challenges that held hemp back and allowed cotton and nylon to rise in prominence. But once separated these silica rich hurds can be mixed with lime and water to make hempcrete. It's not a replacement for structural concrete - it's compressive strength is only 1/20th that of standard concrete, thus it's use is as a wall of flooring material rather than a structural material. Since it is a cellulosic material, I would compare it to wood.

But as a wall material, it has some impressive characteristics. It is seven times lighter than regular concrete, is waterproof (when used above grade), fireproof, and has good insulative properties. But to my mind, what makes it most impressive is that it's actually carbon negative - it can sequester carbon, since, like other plant products, the hemp crop absorbs CO2 gas as it grows, retaining the carbon and releasing the oxygen. It is also 100% recyclable - you can actually grind it up and use it for fertilizer!

Of course all these developments will take place outside the United States due to our laws against growing hemp. Incidentally, the reason it's not grown has less to do with drugs than corporate power. William Randolph Hearst had large holdings of timber which he used to provide the wood pulp for his newspapers, and was afraid that hemp would undemine his business. So he began a media campaign to demonize hemp (and marijuana - the infamous "reefer madness" of the jazz clubs). He was assisted by the Secretary of the Treasury, Andrew Mellon, and the DuPont family. Mellon had invested heavily in DuPont's nylon material, and eliminating hemp would provide a huge market for synthetic nylon. So America has a long history of "free market" capitalism being shaped and dictated from oligarchs on high.

More on hempcrete:

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