Earthbag:

Earthbag construction was started in the USA more recently than the other techniques mentioned above. Polypropylene bags are filled with slightly moistened dirt and tamped into place arranged into an overlapping pattern. For walls rows are sometimes secured with barbed wire. Plaster protects the bags from the elements.

Benefits:

• Easy to learn
• Inexpensive materials
• Good for places where your soil may not be appropriate for other types of earthen buiding
• Good for domes and other curved structures

Building:

We don’t use earthbag construction for whole walls at Pun Pun because with adobe we don’t need to buy any materials but we can see the benefits of using earthbag in certain applications and areas. It can be especially beneficial in desert areas of places with insufficient adobe mud. We use it often for making benches, sitting spaces, furniture, etc. It works well because making the amount of brick you would want for a bench can be a lot and cob has to take time to dry whereas earthbag can be done quickly in one day and fills a large amount of mass.

Dig up a pit of dirt (does not need to be clay-rich but helps if it is) and add a bit of water to moisten the mix but only to make it moist, not wet. It should just hold a form if squeezed into a ball. If too wet, will take too long to dry.

Dump into a polypropylene bag (usually old feed or manure bags) that is set up in place where you want to place it for the wall. (Earthbags can be used as foundations in places where you do not have to worry about a termite barrier).

Fill until about 2/3 to 3/4 full where you have enough room to fold over the top of the bag and no dirt will fall out. Fold over the top as tight as you can and tip over and into place in wall. Stomp on it first to let the dirt expand out.

Continue with the next bag up next to where the last one was laid. If you come to a place where there is a end to your wall, turn in the bag so the folded side will fold inward. This will make it more stable as the weight will press it into the next brick instead of out on the fold.

When you finish your first layer, tamp with a heavy object. We use a large wood stump (with no sharp edges which can bust the bag open) with two smaller wood branches attached to the sides. Some people make tampers from concrete as well. The idea is that if you use moist soil and tamp it hard, once it dries it will act much like one large brick. I still will have the bag around it as you do not take them off and you plaster over them to protect them but the dirt itself holds its own form. It is still important to protect the bags, however, since polypropylene if exposed to the sun rays disintegrates quickly.

If you are simply making a bench or furniture you can set the next layer just on top of the last. If you are building it up as a wall you probably want to add barbed wire between rows to link them together as you do not use a mortar in this kind of building.

Every layer should interlock just as you would with bricks to eliminate break lines.

To plaster on bags:

Some people use chicken wire and you may need to for walls. We use a thick clay-rich mud/straw mix such as the one in the wattle-and-cob recipe above directly onto the bags. It is important that this is thick especially on furniture in places where the edges will get a lot of wear and that they are interlocked pieces of wattle-cob as to not chip off with extended use, exposing bags underneath. Then can plaster over this as you would any earthen wall.