Posted on July 11 2011 by Leo Wettenhall

Geopolymer Stones & Earthbags

Voting is heating up at The $300 House Open Design Challenge. This design challenge started out as an idea described by Vijay Govindarajan and Christian Sarkar in a blog post at the Harvard Business Review. They proposed that it might be possible for a simple home to be built for less than $300.

After looking through all the designs I can’t imagine any of them costing less than $300, except for some of the earthen homes.

Vote for Owen!

Earthbag design-build expert Owen Geiger has two three designs entered in the competition and they are doing well, but every vote gets him closer to winning. Can you spare a vote?

  • $300 Earthbag House — What the World Needs Now – An expandable design easily built by novice owner-builders.
  • Stone Dome — $300 Geopolymer Earthbag Dome – My personal favorite, a synthetic-stone earthbag dome (pictured here).
  • Update: $300 Geopolymer CEB House – Just hours after posting this article Owen let me know of a third entry. CEBs are compressed earth blocks.

Geopolymer Stones & Earthbags

While I’m a big fan of domes, what caught my eye was the building material - a geopolymer earthbag.

The Geopolymer Institute has been trying to recreate a building method they suggest was used to build the pyramids of Egypt. What they (re)developed (depending on your point of view) was a way to build artificial limestone stones from a mixture of limestone, kaolin clay, sodium carbonate, lime and water.

You basically mix the stuff up, let much of the water evaporate, then tamp the semi-moist mixture into a form – or earthbag! After the stuff cures you’d have something as strong as stone – without the need to quarry and sculpt blocks. You could also think of geopolymer as a cement, but without the large amount of energy input required to make modern cement.

While the whole Egyptian pyramid piece would be an incredibly important historical puzzel to solve, I really think the value of (re)discovering this low-cost & low-tech building method could far outreach solving the mystery of the Great Pyramids.

Owen Geiger’s adaptation, packing earthbags with a geopolymer material, could make this building method even more accessible. Earthbags also provide more flexibility than wooden forms because all sorts of shapes and structures can be built by stacking up earthbags.

Below is a video from the Geopolymer Institute that shows how a giant synthetic limestone block is made. The jury in my head is still out on the whole pyramid debate – so while this building method seems so much more plausible,I’m not going to let it distract me from the material itself.

9 Responses to “Geopolymer Stones & Earthbags”

  1. Owen Geiger says: May 18, 2011 at 6:49 am

    Thanks for recognizing my work. I added a third design today called $300 Geopolymer CEB House. http://www.jovoto.com/contests/300house/ideas/12512

    You can make CEBs out of the same material in a standard CEB press. They would turn to actual stone. It would be manmade stone, but still 100% natural using the same materials and chemical process as in nature.

    Reply

    • alice says: May 18, 2011 at 9:15 am

      Just wondering if this stuff can be used to make an outdoor fireplace, either by using a mold or making individual blocks. I had thought of using cob but this sounds more weatherproof. Is there anything about the actual material that would make it unsuitable for use with fire?

      Reply

      • Michael Janzen says: May 18, 2011 at 9:53 am

        Owen will have a better answer than I, I suspect… but as someone with a background (and degree) in ceramics I’d suggest doing some careful testing first.

        Limestone (calcium carbonate) is a flux in glazes and clays. Kaolin is a very pure clay and typically has a very high melting point. Ceramic clays and glazes are basically just different mixtures of silica, clay, and fluxes. So… this brick might melt in a fireplace or it might not depending on the proportions of the ingredients.

        Fireplace brick are also pre-fired and have a large quantity of sand to help the clay body take thermal shock (fast temp changes). Since these are unfired, the first time you fire up the firebox you’d probably want to heat it up slowly to allow the clay to vitrify (or mostly).

        You could also try pre-firing the brick – which would probably be a smarter idea since if one cracks or explodes (like in bust apart suddently – nothing too exciting) it’s not already in your flue or firebox.

        Might be something worth testing though. Take a brick, stick it in a kiln, crank it up slowly and see when/if it melts.

        Reply

      • Owen Geiger says: May 18, 2011 at 6:33 pm

        Making bricks seems like your most practical option. Limestone isn’t required. It’ just part of one “formula.” There are geopolymer recipes/products for all sorts of high performance industrial and military applications. But realize this isn’t some hobby level project. It would require a good amount of experimentation and testing. I predict more DIY resources will gradually become available on the Internet as this technology matures.

        Reply

    • Michael Janzen says: May 18, 2011 at 9:43 am

      Thanks for the update Owen. I’ve added it to the post. I still prefer the geopolymer earthbag dome design – but I can see how the compressed earth bricks could be a very useful building material in some applications. Thanks again!

      Reply

  2. alice says: May 18, 2011 at 9:04 pm

    Sounds like I could make the firebox using more appropriate bricks but still do some decorative stuff around the outside of the fireplace with this stuff, if I ever understood it that is! I want to make a dragon shaped stove. Another friend has suggested I make one out of bricks with a bit of concrete around the outside to make it more shaped like a dragon, then make a bunch of glazed scale tiles to put on it. I like it, but don’t have the resources to make something like that. Be a neat project though.

    Reply

    • alice says: May 18, 2011 at 9:05 pm

      Oops, I mean a dragon shaped fireplace. The dragon shaped stove idea is a different metal working project.

      Reply

    • Owen Geiger says: May 19, 2011 at 9:57 pm

      The simplest solution for making one small stove is to get Kiko Denzer’s Earth Oven book and buy a few fire bricks for the hearth.

      Reply

  3. SteveR says: May 20, 2011 at 9:44 am

    You don’t have to go so far away to find a similar material which was used in the US. It’s called ‘tabby’ and the main material were mussel shells ( used to create a lime as well as a binding agent)

    You can learn more about how it is made and its historic use in the US here: http://www.thehenryford.org/research/caring/tabby.aspx#prepare

    There are some examples on Hilton Head island in South Carolina ( I am sure there are others). The building is long gone but the tabby foundation remains intact.

    Reply

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