1. TLP

    TLP Junior Member

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    Hi new here.....I been playing around with hempcrete wall construction. I've read due to its high silica content (like no other cellulose plant) and strength due to its length (since it is tall compared to its short, wide, marijuana cousin) of the "herd or shiv" inside the surrounding base stalk, binds well with hydrated calcium or lime. As it absorbs CO2 over years, or carbonates back to rock form, the hempcrete becomes very hard and a superior insulation. It is difficult to find it currently although some states have legalized its growth like CO in the USA. The only other option until states like this mass produce and figure out a cost effective way of separating the shiv from its outer fiber (stalk) is to import it from Europe which is not a reliable path I am finding, high embodied energy, requiring a long lead time, and high expense. All the elements a home builder like myself do not want to deal with.

    Question to the permies, and I am not knowledgeable about plants, is there another wood found abundantly in the USA that has a high silica property? I've read, although I have seen no documented proof, that the calcium replaces the silica over time (not that I understand exactly how that happens) and what benefit it is as a building product. There is also “light-earth”, needs the same support frame such as studs or sticks as hemp. It has been in existing a long time, woodchips with a clay binder I am thinking may be a more cost effective path in the USA just not sure it performs as well as hempcrete.
    The ability of high silica in hemp to remove CO2, improve indoor air quality and the atmosphere, harden like a rock and maintain good insulation properties is very appealing. Begs the question of the credibility of the amount of CO2 absorbed that you see on internet searches being real, and whether or not a domestic cellulose would perform just as well in strength and insulation?

    Thanks in advance for any comments.
     
  2. bazman

    bazman Junior Member

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    You might look at tall grasses as I know some like setaria grass have a higher silica content. These might be a whole lot easier and cheaper to source.
     
  3. S.O.P

    S.O.P Moderator

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    Bamboo fibre?
     
  4. TLP

    TLP Junior Member

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    Bazman & SOP are correct. While researching the setaria grass I ran across this here:

    Silica composes 71 percent of the ash of Equisetum telemantia, 51 percent of the
    straw of barley, 67 percent of the straw of wheat, and 46 percent of the straw of oats . The native grasses and weedy grasses as well as the cereal crops have varying amounts of silica.

    "Straw of wheat" is readily available in bales in my locale and 67% not to shabby. They say because the hemp hurd grows tall it has a high tensile strength compared to others but, the hurd I have imported from Europe is short with loose fibres(hair from the stalk which makes a good batt insulation, not hempcrete), meaning they did not separate the two well). So in my mind a long silica straw would work as well and since hempcrete is an insulation tensile strength does not matter, you need a wood frame to support it is where the structures compression and tensile strength comes from. Looks like bamboo will work too. The attraction silica in the plants have to lime (calcium oxide and silica plants is the acidic in nature from what I understand) Other glues or binders like certain clay, magnesium oxides, additives would help bind. This is how high strength portland cement is made with a high carbon foot print I am trying to steer clear from.

    I keep reading on the so called "green" sites of the high levels of carbon dioxide (CO2) the IAQ meters are finding from factory manufactured products placed in homes. There is also a trend to seal homes up to German (Passivhaus) standards in the USA, reduce energy cost to net zero and the carbon footprint. What people don't get is when you air seal a home with known toxins and low ventilation your are asking for trouble. So I keep reading how the fix is to add more mechanical devices that pull outdoor air and push interior air across a heat ex-changer called a HRV (Heat Recovery Ventilator) some of which add moisture like a humidifier called ERV (Energy Recovery Ventilator). Had they used all natural materials or a negative CO2 material with lime, problem solved. You can also create a natural ventilation systems by creating a heat ex-changer with your masonry or rocket heater and xchanger, just cross the intake and exhaust or use manual valves to add recovery heat when in taking outdoor air without the use of electricity and more toxic factory built products. Of course some outdoor air may be of a lower quality than indoor.

    Anyway, think I'll cast up some lime-strawcrete do a u-value test see the difference to hempcrete. I would think there would none.

    Thanks for the help :)
     
  5. sweetpea

    sweetpea Junior Member

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    By "hempcrete" you are talking about a cobb-type mud/stucco? I've seen versions of it made from sawdust of woody plants. Not sure where you are in the US, but California is full of Bottlebrush trees, the woody stems are high in silica, and if ground into sawdust could be used. Bottlebrush is also an excellent permaculture plant, bees and beneficial insects are crazy about it. But it has to live where there are mild winters.

    "Horsetail - bottle brush Ideal for containers, but cut back in summer to prevent spores. Yields a yellow ochre dye. Stems have high silica content and dry used to scour metal and polish pewter. Summer 2oz of dry or fresh herb in 1 1/2 pts water for 20 min., and soak nails to strengthen. Makes good conditioner and rinse for hair. Storehouse of vitamins USE CAUTIOUSLY"

    https://possumsal.homestead.com/Health/0000.html

    I think hops vines are, too, and when dry they would have a more straw-like texture.
     
  6. Pakanohida

    Pakanohida Junior Member

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  7. sweetpea

    sweetpea Junior Member

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    Wow, that is scary expensive stuff!
     
  8. Pakanohida

    Pakanohida Junior Member

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    The fibers are used by hollywood to make molds for masks and appliances to be worn in movies. Lot easier to grow it yourself or get the pet stuff.
     
  9. sweetpea

    sweetpea Junior Member

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  10. eco4560

    eco4560 New Member

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    Nice house but the price tag is over the top! That's probably $1000 per brick!
     
  11. TLP

    TLP Junior Member

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    Wow, I hope my production homes sell for that. Santa Barbara use to be nice back in the 70s but has got so populated it is in no way shape or form worth the land price, which is what that price is mostly.

    Sweatpea thanks for listing some other plants that may work. Hempcrete is alot like cobb-type mud/stucco except no soil is used. Some add sand to aerate it to get higher r-values and cost down. Some that want to see the hurd natural plant will lime wash the interior, a lime stucco protects the hempcrete from impact, moisture, temps.....

    Looks like Pakanohide needs to try and order some from hempcrete tech in CAN, they I have found to be the least reliable and have the longest lead time, not good for a natural production home builder such as myself...there is another one close to Chicago, IL, American Lime Technologies, that was the owner of HCT now two different companies. Both have little good to say about each other and get the left overs from Europe, and you may be waiting a long lead time for a shipment that just so happens to be heading to the states when it is full of junk herd. Pet grade or short herd with high amounts of fibre won't work in walls and roofs, you want long herd or plants like straw with high tensile strengths, no weak fibre or stalks. In the majority of US it is illegal to grow it, the ones that do have no competition and charge a premium. That is just the beginning, you need a binder to cast it into a home. The European herd suppliers will swear you need their "pure hydraulic lime", NHL 2, NHL 3, NHL 5, 50 lb bags shipped to you which is bull! 1.5 bags per bag of hurd, the binder cost 2-3 times the herd. By the time you add up the all cost you are 3-4 times what you could build a 2x4 house out of. Last we laid out a cost comparison for a 1500 sq foot house, 2x 4 is $13,000, hempcrete $29,000 not including shipping since I got disinterested in getting the shipping cost of course and never asked. I created my own binder. So I guess I don't agree with the statement "this stuff is easy to source" but please do show me how?

    I think a much better alternative to source is use some of the other plants we identified on this thread that are readily available at your location rather than the high carbon foot print and cost of shipping it locally or across seas.

    Just amazing all the law suits and deaths flying around the USA from toxic foams like spray polyurethane foams and other elastomer seals and sealants used in wood framed homes to air seal them to paasivhaus .6 or less air changes per hour for energy efficiency, vs using a monolithic cast in place hempcrete or earth construction that is natural, safe, little to no gaps that need sealing. Then most think ventilation systems get rid of these toxins. Things are a mess in the USA and all they have to do is look at history and good ol mother nature :)
     
  12. Pakanohida

    Pakanohida Junior Member

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    Location, Location, location... that's the reason for the price of the house. The house has utterly nothing to do with it, the properties in Santa Barbara go for $500,000 to $2,000,000.
     
  13. porkbrick

    porkbrick Junior Member

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    as an arborist with access to a near unlimited amount of woodchip, i have been very interested in the feasibility of a lime/woodchip building material. i dont see any reason why the same binder used in hempcrete wouldnt work with wood fiber. wood, being more dense, would yield a lower R value i would guess. can anyone shoot down my dream before i go out and make test batches?
     
  14. TLP

    TLP Junior Member

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    I just did a post #9 on sweatpeas thread explain wood chips here if your into technical reasoning: https://forums.permaculturenews.org/showthread.php?18587-Stepping-Stones-with-embedded-wood-chips

    Wood chips will work to aerate a concrete mix, lets call it chipcrete. There are a lot of binders to choose from, lime is one, clay, lime(CAO), pozzolan fly ash, magnesium(MGO), portlant cement(OPC) being the most toxic to manufacture and responsible for a large part of building industry or carbon foot print).

    12" walls are typical with a r-value 30 ish. I don't think that changes alot between hemp, straw, chips, etc......If you try and bond lime alone to wood it will crack. I tried it as an air and moisture sealer. It needs a fiber to hold it together, thats where hemp, straw, chips, etc work. Hemp is suppose to be the highest in silica, and strong in tensile since it grows tall in just about any environment.....It's not that strong tho in tension, straw, chips, etc...do fine and if more available by all means use it. Most cements come aerated too, so if you want more r-value, perhaps less wall thickness try it due to air being a good insulator. In the US look for high calcium lime, or type s mortar which has more MGO in it than type N. Portland cement type 1A allows more air infiltration then type 1 but has lower compression. Since we need a frame for these cretes, I use 2x8's on 24" centers, we are not using cretes for compression the 2xs do that. The crete does reduce racking.

    I seen on your other thread you are going earth bag, the chips may help aerate the sand-silk mix a bit to provide a thermal brake and increased r-value.
     
  15. 9anda1f

    9anda1f Administrator Staff Member

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    Wow TLP, thanks for submitting such an information-packed post!
     
  16. porkbrick

    porkbrick Junior Member

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    thanks for the excellent info. i mixed up a test batch this weekend, woodchip and shredded redwood bark mixed with 3parts lime putty, 1part portland, 2parts clay, 2parts sand. im going to let it cure for a week and see what happens. i was intending to use sawdust in the mix but didnt have any on hand at the time.
     
  17. sweetpea

    sweetpea Junior Member

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    I have the Cob Builders Handbook by Becky Bee that has a lot of good building tips for using any of these kinds of natural mixes, particularly how to slant the stones in the foundation so that the cob doesn't slip away. It talks about how deep and wide to make the stone foundation. It's just wall-to-wall straight info about the construction.

    These cob-type walls also need big eaves to protect them from the rain, and with thick walls it makes the structure inside dark unless you plan for enough windows. I can't find the window-to-wall ratio that works best for this, but there probably is one. On the coast where we are, days can be overcast because of the fog, and a dark interior would be very depressing. Our windows are about 1.75 meters (5 feet) tall and 1.5 meters (42 inches) wide, plus sliding glass doors that really make a difference.

    This book also talks about termites getting through the cob and eating the wooden structure inside, but this is not talking about a crete mixture, just clay soil and straw or sawdust, etc.
     
  18. TLP

    TLP Junior Member

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    Sweetpea, what is cob typically made of straw and soil and thats it? I guess if you get the straw content to a point where the soil does not crack?

    Check out this home for 1.2 million made out of toxic PU foam....COB would have been a much better choice. https://www.zillow.com/blog/bethesda-mushroom-house-163230/

    I'm pondering the window ratio myself, I think the general rule for solar passive is no more than 40% of the facade SF for energy efficiency but, people love their windows and are not willing to pay high prices for triple panes.
     
  19. TLP

    TLP Junior Member

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    I was on a so called "green" website yesterday that has limited articles on natural building methods, debating one of the "advisors" use of rigid foam to insulated the bottom and perimeter of a basement wall or footing. The rigid PU foam is toxic, does not flex, has 60-80 psi compression. Hemcrete or perlite and lime compression would be 3-5 times that of foam per inch, an r-value a little lower 3-5 per inch, but better insect protection, water managing and drainage, fungi and fire resistance, etc..

    I developed a natural strawcrete air sealant, here showing sealing a garage room addition that is much better than spray toxic foam in a can and much cheaper.

    Why we in US have adopted foam defy's logic. We are seeing a shift of more natural building methods but it's like pulling teeth, or some just don't understand it or never heard of it, like building code enforcers. Code is highly influenced by manufactures.
     

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