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Archive for August, 2010

Woodchip/light clay is a traditional building material in Germany and other European countries. It’s typically used as infill between timbers in post and beam construction. I’ve been told that bags of pre-mixed materials are standard items in building supply centers, and blocks can be made to order. The drying time, shrinkage and labor are less than using straw/clay.

Although no one to my knowledge has used woodchips and light clay in earthbags, this building system has good potential and so I’m planning to build a test wall — maybe one wall of a garden shed.

Woodchip/Light Clay

Woodchip/Light Clay

The building process is very simple. Thin clay slurry is mixed with chips and used as fill material in the bags. Clay holds the chips together and protects the wood from insects, mice and fire. Clay also absorbs odors, moderates humidity levels and provides thermal mass to help stabilize indoor temperature.

Advantages: Low cost, possibly free materials; lightweight; reduced labor; faster to build than soil-filled earthbags; easy to mix; very little tamping; non-toxic; locally available natural resources; sustainable and recyclable, approximately R-2 insulation.

Chips can be up to 2” diameter. They should be bark-free, since bark decomposes rapidly. Chips can be dry or green, and often can be obtained for free or very low cost from city recycling programs or tree trimmers. The ratio is 4 parts woodchips to 1 part clay slip.

One drawback is drying time — about 8 weeks for a 12” thick wall during warm weather, and even longer for 16” walls. Builders in cold climates would have to plan accordingly to allow adequate drying time and prevent freezing. And like typical earthbags, walls must be protected from the elements with adequate roof overhangs. Risk of moisture damage probably rules out the use of woodchip/light clay for domes.

Photo credit Frank Andresen
More details are available here.

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Earthen Hand Dome in Mali

Earthen Hand Dome in Mali


Scott Howard organized a workshop in Dogon Country, Mali, last winter. He built this unique dome with the help of workshop participants and some of the villagers there. The majority of the structure was completed during the two week-long workshop. It is a catenary arc about 16.5 feet tall with a loft. Serving as a library for many villages in the area, it is the first earthbag dome in Mali. Earthen Hand natural building offers a variety of international workshops these days.

I found the above photo in Scott Howard’s article A Wholly Different Way of Building at the Permaculture Research Institute of Australia website. Scott raises a lot of questions in this fascinating article on the best ways to waterproof earthen domes.

Photo credit: Earthen Hand

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We continue to find amazing uses for polypropylene tubes and bags. In this case, PEMEX oil company in Mexico used large poly tubes (referred to as Geotextile Tubes or GT in the original article) at one of their oil facilities. One part of the project involved filling 7.8m circumference poly tubes to support oil pipelines, whose bases were eroding away. The tubes were pumped full of sand using “4-in. discharge-diameter slurry pumps with volume discharge rates up to 40-50m3/hr with 10–30% of solids.” The unique qualities of poly tubes helped create a successful project. As the tubes filled with sand, they naturally conformed to the irregular surface and varying height below the pipe.

The second part of the project is equally interesting. To prevent future beach erosion, the same poly tubes were placed parallel to the shoreline. As waves hit the tubes, a wave energy reduction zone is naturally created. The resulting turbulence induces sand accumulation on the shoreward side of the tubes, ensuring ongoing natural accumulation of sand.

Read the full article at GeosyntheticsMagazine.com

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The group at Konbit Shelter has made phenomenal progress on their triple dome in Haiti. Be sure to check out their blog for full details and, if at all possible, it would be great if you could find a way to support their project.

Konbit Shelter in Haiti

Konbit Shelter in Haiti

Konbit Shelter in Haiti

Konbit Shelter in Haiti

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Often plaster mesh is not required, but when it is needed it’s useful to know which type of plaster mesh is most affordable – chicken wire, plastic mesh or fishing net. I think stucco mesh is overkill and so it’s not covered here, although it’s often required by code and so you’ll have to plan for this if your building regulations call for it. For ease of checking prices on lots of items quickly for cost estimates, I suggest an online site such as Lowes.com.

Poultry netting (chicken wire): $14.97 for 4’x50′ roll = 200 sq. ft., which is 7.5 cents/sq. ft. (narrower, shorter rolls are much more expensive).

Plastic mesh: (low cost option) $13.93 for 4’x50′ roll = 200 sq. ft., which is about 7 cents/sq. ft.

Nylon fishing net (priced locally): $3.78 for 6’x52’ roll = 312 sq. ft. when stretched out. That makes it about 1.2 cents/per square foot. (You might even be able to obtain used fishing net in decent condition for free.) Like plastic mesh, fishing net won’t rust and so it’s durable in wet climates.

At about one sixth the cost of poultry netting and plastic mesh, fishing net wins hands down. And think how strong it is. It’s used to pull out heavy loads of fish year after year and stand up to underwater use. So, fishing net is my first choice for affordable plaster mesh. Photo below shows typical 1.5″x1.5″ spacing.

Nylon Fishing Net

Nylon Fishing Net

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Glass Block in Earthbag Wall

Glass Block in Earthbag Wall

Glass block adds a nice decorative touch to earthbag walls. The building process for adding glass block is fairly simple: Make wood frames much like window bucks, only smaller. Earthbag walls are quite thick, so you will probably want double glass blocks – one near the interior, one near the exterior. This creates a wide, strong surface to support earthbags above. To do this, build 2×4 frames (bucks) for each glass block. Plan ahead so you know where to insert the frames in the wall, and then set and level the frames where you want them. Frames are held in place by earthbags pressing against them. Curve the bag ends that adjoin the frames by pinning corners of bags out of the way to create gently rounded edges in the plaster. Set the glass block in place after the walls and roof are finished. Add four nails behind each block to hold in place, and then plaster around the blocks.

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From time to time we answer reader’s questions.

Q: Why aren’t people making roofs from earth using domes or Nubian vaults? In impoverished areas the cost of a tin roof is sometimes a year’s salary.

A: Domes and vaults evolved in extremely dry areas of the Middle East, where wood was scarce and lack of rainfall wouldn’t destroy the earthen roofs. People are often captivated by the unique look of domes and vaults and want to build them in other climates. Earthbag building extends the possibilities beyond desert regions, yet still domes and vaults are somewhat vulnerable to moisture problems, and so if this is your plan then you’ll want to design and build them very carefully. Options include using cement stabilized soil or waterproof materials such as lava rock as fill material, cement plaster and elastomeric roof coating. Also, eyebrows over doors and windows are recommended to provide extra protection for these areas. Building a roofed dome is probably the best option in rainy climates.

So yes, wood roofs/metal roofing are costly, but you can see that domes and vaults also have costs: cement for stabilized soil, cement plaster, roof coating, eyebrows. There’s no free lunch unless you want to live in a grass hut or something. Plus, earthbag vaults are tricky to build and therefore limited to small spans.

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