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.
– 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.