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‘Hempcrete’ is a small way to fight climate change (no, you can’t smoke it)

  • Hempcrete Courtesy—Mil Hollow Works

Monitor columnist
Published: 3/30/2020 2:29:36 PM

The weirdest thing has happened to me since the COVID-19 crackdown arrived. I’m actually feeling less stressed.

Why? I think it’s because I can only consider one existential crisis at a time and apparently my lizard brain is less afraid of disease-fueled social collapse than it is of global climate catastrophe.

In other words, a Really Bad Thing has replaced a Really, Really Bad Thing in my anxiety synapses, and I’m feeling better for it.

However, that’s not to say the Really, Really Bad Thing has gone away, because it hasn’t. Hard as it is to think about right now, we still desperately need to emit less greenhouse gas and make big changes to cope with climate change.

One small attempt to prod some of those changes did pretty well at town meeting season. An activist group called the Citizen’s Climate Lobby put non-binding articles before a number of towns asking voters to support the federal or state government establishing a “fee to be paid by vendors of carbon-based fuels based on their emissions,” with the money divvied among all state households. They called themselves the Carbon Cash-Back Coalition, and by their tally 23 towns passed the article while 10 rejected it.

I’m not sure if it’s on the warrant of any places that have postponed town meeting due to COVID-19, so the final result may differ.

A fee based on carbon emissions is generally seen by economists as the most efficient way to use market forces to reduce greenhouse gases. Using this warrant article to create a bit of political pressure is one way for this sensible but politically unpopular system to move forward.

Another way is to change some basic practices such as our building materials, which brings us to a very interesting product called “hempcrete.”

“I like to call it hemplime. It shouldn’t be called ‘crete’ really but that’s the name it has,” said Aaron Ward, the carpentry instructor at Mill Hollow Works, which gives a variety of courses in a timber-frame barn that, says the website, “Keene locals may know as the old Ellis Farm.”

Ward is scheduled to teach a class at Mill Hollow Works this summer on how to make and use hempcrete, which is not a load-bearing material like concrete (that’s why he doesn’t like the name) but is an insulation. The class schedule is a bit scrambled right now, like everything else, so check the website (https://millhollowworks.org/) for details.

Hempcrete is made by chopping up hemp plants and mixing them with a lime binder to create a material that can be cast in molds. It is often made into bricks with high insulation value or used as insulating fill inside walls. Either way, it can replace Fiberglas or some petroleum-based products.

Because it uses plants, which have pulled carbon out of the air as they grow, and then locks them inside material that last for decades, hempcrete can be carbon-negative. Using more plant-based material in construction in place of material that requires the release of carbon when manufactured – in particular, steel and concrete – is one of the steps we need to take to stop loading up the atmosphere with heat-trapping gasses.

That’s why I’ve written about manufactured timber, which glues together smaller pieces of wood to create replacements for steel I-beams and concrete foundation. Hempcrete is a small example of what we need to do.

“Twelve inches of hempcrete has an insulation value of about R24,” said Ward. That’s a quarter or so less than the same amount of Fiberglas, so it could require more material. “It’s fireproof, hypoallergenic, mold and mildew resistant. Plus, I like the look of it – it’s a very soft, very calming look.”

You definitely can’t say that last one about Fiberglas.

Hemp, of course, has a complicated history here. Despite everybody in New Hampshire saying “live free or die” at the drop of a hat, we have been perfectly happy to prevent people from freely growing hemp because the relationship to cannabis spooks us.

That’s the first thing everybody asks, Ward says: “You can’t smoke hempcrete, you can’t light it and get high!”

There’s another complication, though. The type of hemp you need for hempcrete is different than the type you need to make CBD oil.

“Hemp for CBD has different seeds. It’s only 2-3 feet high, all buds and leaves, small stalk,” said Ward. The hempcrete plant has a long stalk because that’s what you need to chop up and mix with lime. That crop is grown in Canada, China and parts of Europe.

“We need to get more people onboard growing hemp in the U.S.,” said Ward. That would lower the cost of hempcrete.

Another thing that would help brings us back to the town meeting item above: Putting a price on carbon emissions would raise the price of steel and concrete by acknowledging the damage they do. That would give more incentive to produce and use alternatives that are carbon-negative. 

That could also create a new cash crop for farmers, assuming it can get disentangled from the modern version of Reefer Madness. A win-win, as they say.

There now, don’t you feel less stressed?

(David Brooks can be reached at 369-3313 or dbrooks@cmonitor.com or on Twitter @GraniteGeek.)


David Brooks bio photo

David Brooks is a reporter and the writer of the sci/tech column Granite Geek and blog granitegeek.org, as well as moderator of the monthly Science Cafe Concord events. After obtaining a bachelor’s degree in mathematics he became a newspaperman, working in Virginia and Tennessee before spending 28 years at the Nashua Telegraph . He joined the Monitor in 2015.



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