Lightweight, Insulating Geopolymer Earthbags Part 3

Stone House by Askjell (click to enlarge)
Stone House by Askjell (click to enlarge)

I’m proposing using a combination of ferrocement, earthbags and porous geopolymer to build durable, affordable housing. In a nutshell, earthbags filled with lightweight geopolymer cement are fastened to a rebar or bamboo frame and then plastered with geopolymer cement. This is distinctly different from heavy earthbag walls, and much different than regular thin shell ferrocement that often does not provide sufficient insulation and lacks the visual appeal of houses with substantial walls. The end result would be an incredibly durable stone home made with natural materials.

First, let’s do a quick recap of Part 1 since it’s been a few months (wow, time flies) since I posted my first thoughts.
Geopolymer is highly desirable because it’s an affordable, natural material that turns to actual stone and is fireproof, insect proof, rot proof, bulletproof and can last for centuries.
– Geopolymer is superior to Portland cement in a number of ways: far lower carbon footprint, less cracking, more resistant to corrosive elements such as sea salt, excellent frost resistance and durability in cold climates, rapid set binders available.
– Porous geopolymer is light weight, easy to work with and insulating. No additional insulation is needed.
– Recycled waste materials such as slag and fly ash can be used to make geopolymer, thereby making the material carbon neutral.

In Part 2 I posted a close-up photo of porous geopolymer and covered a few of the building basics: minimal tamping required, smaller diameter bags or tubes save materials, a keyway can be formed to lock courses together, flatten walls to reduce plaster work, bag material could be removed before plastering or left in place.

Now, on to Part 3. Here is the summary of the basic concept:
– Build a rebar or bamboo and mesh frame to guide the shape. This provides plenty of tensile strength and enables almost limitless design possibilities.
– Use tubes or bags to form walls 6”-15” thick. These could be made out of a wide range of materials, including polypropylene (typical sand bags) or natural materials such as cotton, jute, etc. Tubes would be faster than bags. Recycled bags may be available and less expensive than tubes. Mesh material will provide superior bonding with the finish coat and eliminate need to remove the bag material before plastering.
– The wall thickness depends on the climate and other considerations. Use thicker walls in colder climates where more insulation is needed.
– Fill the tubes or bags with lightweight, insulating geopolymer. The consistency would be similar to ‘stiff’ (not too much water) pumicecrete (pumice-crete).
– Pumicecrete is a standard product and provides a good point of reference, although many similar materials could be made using geopolymer mixed with different insulating materials in addition to scoria/pumice: perlite (perlite cement), shredded recycled polystyrene, vermiculite, etc.
– Porous geopolymer (lightweight aerated cement or concrete) can also be made with a foaming additive to produce tiny air bubbles in the cement. Porous geopolymer can be used alone or combined with scoria or other materials.
– Porous geopolymers have unique passive cooling properties which can improve thermal performance and reduce the heat island effect in cities.
– Tie the tubes or bags to the frame as they are filled.
– Flatten the tubes or bags slightly as they set up. This will greatly reduce plaster work.

Key advantages:
– No need for contractors or industrial size compressors and high-pressure spray rigs. Finish plaster can be sprayed on with a Mortar Sprayer.
– Nearly limitless design possibilities as mentioned above.
– This method has the advantages of ferrocement and earthbag building without any major drawbacks that I can think of: 1. faster construction and less labor than earthbags; 2. more substantial, bulletproof and more insulating walls than ferrocement.
– A second ferrocement frame could be added for seismic regions, but it shouldn’t be needed in most situations.

Part 4 will discuss how the building process can be mechanized to speed construction.

Note on the photo: I chose this photo to illustrate how almost any shape can be built — from ‘boulder houses’ like this to conventional looking structures of all kinds.

Image source: and

10 thoughts on “Lightweight, Insulating Geopolymer Earthbags Part 3”

  1. You forgot to discuss limecrete, variations have been used for thousands of years. Also, the Romans used scoria and limecrete, look at their ruins still standing…

    So, when and where are you going to start construction; until a building is standing somewhere using the methods you discuss it is just illusion, especially since there are so many structures standing already using the other methods….

    I look forward to seeing the construction and finished product photos and video.

    • Yes, this topic is covered in detail on my Geopolymer House blog. Examples include both historic structures and new developments.

      As explained on my blog, it’s an open source project to disseminate the information to a wider audience. I can’t do it all as you seem to imply. Thousands of readers have already visited the site. No doubt some of them have decided to build this way since I get emails every now and then for help on their projects. So it’s an incremental process of development. Step by step more people learn about geopolymer building and gradually the idea spreads. It’s not an illusion. It’s already happening. Maybe you can think of a way to contribute.

  2. The more I learn, the more confused I become about all these building options. I’m tending to rule out earthbag building here in central Texas due to the extreme heat of the summer. Now, after reading about geopolymers, I’m thinking that is a possibility. Will there ever be some “formula” for extreme heat areas for those of us who want to build naturally?
    Would appreciate comments on using insulating geopolymer building tecniques to battle the Texas heat and humidity. And, how do I find the formula for making earthbag building work?

    • Geopolymer is cutting edge and so it’s rather difficult finding the materials and figuring out the details. I started the blog to help sort things out.

      It’s far simpler to just build with earthbags. Earthbag is excellent for hot, humid climates if you follow a few simple steps. Read through my Earthbag Roundhouse blog posts and Patti’s articles on building in hot, humid climates:

      Not sure why you think earthbag won’t work. Our roundhouse is way cooler than outside and we’re in a hot, humid climate. Keep reading.

  3. I wish that everything I knew wasn’t wrong…

    Looks like a great way to build in colder areas. I bet you could structure this over a catenary dome wire-frame of basalt rebar. Like building a bent Tee Pee, forever.


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