There’s No Place Like Home, Especially if It’s Made of Hemp, By Adam Popescu, The New York Times
The Romans have been using it since the days of Julius Caesar, but not to get high. Both Washington and Jefferson grew it.
Now that several states have legalized the use of marijuana for some recreational and medical purposes, one of the biggest untapped markets for the cannabis plant itself — at least one variety — could be as a building tool.
The most sustainable building material isn’t concrete or steel — it’s fast-growing hemp. Hemp structures date to Roman times. A hemp mortar bridge was constructed back in the 6th century, when France was still Gaul.
Now a wave of builders and botanists are working to renew this market. Mixing hemp’s woody fibers with lime produces a natural, light concrete that retains thermal mass and is highly insulating. No pests, no mold, good acoustics, low humidity, no pesticide. It grows from seed to harvest in about four months.
A strain of the ubiquitous Cannabis sativa, the slender hemp plant is truly weedlike in its ability to flourish in a wide variety of climates, growing as high as 15 feet and nearly an inch in diameter. The plant’s inner layer, the pith, is surrounded by a woody core called the hurd. This is the source of the tough fiber, which can be used for rope, sails and paper.
Hemp is typically planted in March and May in northern climes, or between September and November below the Equator. Once cut, usually by hand, plants are left to dry for a few days before they’re bundled and dumped into vats of water, which swells the stalks. Those dried fibers are then blended for a variety of uses, such as adding lime. This creates block-like bricks known as hempcrete.
Industrial hemp contains a mere 0.3 percent of THC (tetrahydrocannabinol), the substance responsible for the buzz when smoking weed. The cannabis present at a reggae fest, for instance, contains as much as 20 percent.
The two strains look different, too. Hemp’s sativa is taller; the shorter indica has resiny trichomes accounting for its psychoactive power. The rule goes: the better the budding flower, the poorer the hemp.
Also unlike pot, you can’t grow hemp in an indoor hydroponics setup; the plant’s deep roots need to spread, so outdoor cultivation is required. The plant’s seeds and leaves can be eaten raw, dried into powder or pressed into oils.
Getting a mature plant in just a few months — with less fertilizer than needed for industrial crops like corn, and without chemical fertilizers or bug sprays — makes the potential for profit huge. As hemp taps water underground, its long roots circulate air, which improves soil quality — another boon for farmers looking to rotate crops.
Full article : https://www.nytimes.com/2018/01/29/science/hemp-homes-cannabis.html