Gravel Foundations for Earthbag
There will be many who refuse to believe this will work. What no concrete? is their never-ending refrain.
Concrete foundations have been around for less than a hundred years. Buildings have been built for millennia. In the eastern Mediterranean it's common to see structures still standing over 2000 years after they were built, without a drop of Portland cement.
Portland cement is not just un-eco (the carbon footprint for producing the stuff is massive). It also has a habit of wicking up water. This is bad news for an earthbag house.
I spent a few sleepless nights over this gravel foundation. Now I'm as pleased as punch with it. If you live in an area that experiences a lot of rainfall nothing beats it. For the doubters, my house has withstood 3 large earthquakes, and is bone dry.
How to make gravel foundations for an earthbag home.
1. Dig a trench half a metre deep. Make sure the trench is wider than the earthbags.
2. Fill the trench with rocks from the surrounding area up to about 20 cm below grade.
3. Cover your rocks with smaller gravel (this prevents polypropylene bags from ripping).
4. Lay two or three layers of gravel-filled polypropylene bags with thick barbed-wire between the layers for tensile strength. Double-bag your foundation layers to reinforce the sacks.
5. Fill in the gaps on either side of the bags with more gravel/rubble. This prevents water wicking up into your earthbag house.
6. Make sure you tamp the bags after each circle is laid. The gravel becomes nice and compact.
7. Protect your PP bags from sunlight (especially the foundation layers) until you put on mud plaster. UV can break down the bags.
This house's foundation system was also documented in the Natural Building Blog.