Lightweight, Insulating Geopolymer Earthbags Part 1

We’ve been discussing Professor Joseph Davidovits cast stone research at the Geopolymer Institute in hopes of applying this concept to earthbag building. You have to admit the possibility of building a house with dirt cheap, natural materials that turn to actual stone and become fireproof, insect proof, bulletproof, etc. is intriguing. [Update: two people have emailed and said they are already building geopolymer earthbag homes.] Just one aspect alone – the desirability of a material that lasts for centuries – well justifies the time and effort to learn more about this subject. We know the basic science of geopolymers is sound. About two hundred labs around the world are working in this field and developing a wide range of products. My new Geopolymer House Blog has extensive information and daily updates.

Let’s think really big for a moment and try to imagine an ideal fill material for earthbags. We’ve already mentioned the desirability of using low cost, commonly available materials that turn to stone. Check. Now imagine using waste materials such as fly ash, slag from iron ore processing, and tailings from mining. Check. (Scientists are already doing this.) Imagine a material with little or no shrinkage when it dries. Check. Imagine a material that uses no Portland cement, because it’s rather expensive and a major cause of climate change. (You can eliminate one ton of greenhouse gas for every ton of material produced.) Check.

Imagine a material that…
– is carbon neutral and doesn’t need a large amount of energy to produce
– can be produced by batching processes similar to those used for Portland cement
– can be applied as shotcrete or by hand
– has rapid set binders
– is resistant to corrosive elements such as sea salt
– is not dissolved by acidic solutions
– has excellent frost resistance and withstands repeated freeze thaw cycles
Check, check, check…

Wouldn’t it be nice to create air spaces in geopolymer with air entrainment additives to increase it’s insulation value? Check. Let’s take it a step further and add scoria, pumice, perlite or possibly rice hulls to further reduce the weight and increase thermal properties. What I’m leading up to is a material similar to pumicecrete that’s made by binding these insulating materials with geopolymer cement. This hasn’t been done yet as far as I know and so the concept needs to be tested, but this general approach could lead to high performance, lightweight earthbag building. Photos show clean ½” scoria and a close-up view showing the porous structure that traps air and improves insulation value.

Small lava rock (scoria)
Small lava rock (scoria)

Close-up of scoria: note porous structure that traps air and increases R-value
Close-up of scoria: note porous structure that traps air and increases R-value

5 thoughts on “Lightweight, Insulating Geopolymer Earthbags Part 1”

  1. How long does the geopolymer take to become stone?
    Owen: Depends on the recipe. The high dollar Pyrament type products are rapid set in a few hours. Layman’s recipes like ours take days, although they start hardening almost right away.
    Would geopolymer work in the Hyperadobe tubes/bags?
    Owen: It could, but again it depends on what materials you’re using. You’d have to use the slower Davidouvits method where the materials are first soaked in a pit. Work out your geopolymer mix before ordering bags.
    Would one layer of geopolymer bond to another even if one layer is already stone?
    Owen: It could. In one of my blog posts I suggested forming a keyway down the center to help join courses. You could think along these lines and maybe improve the idea further (embed nails, etc.).
    Would that bond be prone to cracking?
    Owen: Not sure. However, there would probably be less cracking if you kept building courses steadily with no long delays between courses. That way each course is approximately the same as the previous one. Tamp the walls flat to reduce plaster work. Then use a putty knife to fill the recesses between courses with the same geopolymer.
    Could you make CEBs and let them harden as the wall is being built? Do you think you could get away with out using mortar?
    Owen: That’s what I proposed on my $300 CEB house. But this is a new idea that hasn’t been tested yet. It assumes the slower Davidouvits method. It should work though. Note the CEBs used in my design. They interlock without mortar. This is quite common.

    I guess you could use geopolymer as mortar…

  2. I’m really looking forward to hearing how the first brave soul fares with their geopolymer earthbags. We’re really excited about the possibilities of GP as a potential replacement for Portland cement where permanence is a desirable trait.


    • I think there’s unlimited potential. But there’s a learning curve to everything and that takes time and effort. I’m going to approach a local university soon and see if they’ll do the testing.

  3. For those who are interested, you can google each key phrase in my blog post to learn more. Examples:
    geopolymer fly ash
    geopolymer air entrainment
    geopolymer shotcrete


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