Low Technology Institute

We’ve been working hard on the earthbag walipini greenhouse. Although our weekend workshop got rained out, we’ve still managed to get the foundation trenches dug, the rubble trench poured in, and the first layer of bags laid. Here’s the details.

Foundation

In all, we’ve excavated approximately 48 tons of soil. This has taken about 40 hours of work. Each trench is about 2 ft wide. The outside wall is 3 ft 6 in deep. The slightly lower cold sink area is 4 ft 6 in deep. Each trench bottom is filled with 6 in of gravel for drainage and a perforated 4-in drainage pipe around the exterior.

Trench with wheelbarrow-fulls of gravel dumped in.

Trenches with gravel raked even.

The gravel was brought in by wheelbarrow and carefully poured in. Each load covered about 8 linear feet. To avoid collapsing the wall, a board was laid down to spread the load (note the board in the first picture, above). A hoe was used to distribute the gravel and a gravel rake to even it out. Everything was then tamped hard and flat.

After adding the gravel, the foundation is 3 ft below the ground surface. Note the wooden supports and baulks holding up the soil piles above the trench. They are held by supports at the bottom and cables at the top, connecting it to anchors behind it. This will be removed as the wall gets higher.

Mixing the Fill

Ideal earthbags are filled with 70 percent sand, 25 percent nonexpanding clay, and 5 percent hydrated lime. To be fair, other mixtures work well, and we’re doing a bit of an experiment. We don’t have sand available here, so we’re using straw to bind the clay, which we have aplenty.

To mix the fill, we loosened up about 2 ft³ of clay. To that was added about two scoops of hydrated lime (each scoop was about a quart). An approximately equal amount of straw was shredded on the ground next to the loosened clay, which was then piled on top of the straw. A pointed hoe was then used to pull the fill, chopping the clay and mixing the straw and the clay.

Filling the Bags

Each 55-lb grain bag was pinned in a frame to hold the end open. The fill was dumped into 2-gal buckets. Four buckets were used to fill each bag. As the fill was dumped in, feet and hands were used to smack the side of the bag to settle the fill. Once full, the clamps were taken off and the frame lifted away. One loose end of the bag was tucked inside and the other flap was folded over. The bag was positioned so that the flap side would be snugged up against the previous bag. Once laid down, it was stomped flat. Once an entire row is completed, it is tamped down to be even more compact.

Underneath the bags and between the bags and soil was put a plastic moisture barrier. The bags also have a plastic bag liner. This double barrier will help keep the moisture content of the bags more constant. This helps the stability of the entire wall.

Between each layer of bags, two lines of barbed wire were laid down to help bind the upper and lower courses together.

Buckets o’ fill.

Filled bag.

Flaps folded over.

Bag laid down.

Initial bag flattening.

Nearly finished bag.

Covering the Work Site

To help keep the bags dry and warm, the work site is covered with a temporary roof using the materials that will become the permanent roof. The chickens like to walk over it and look down on the work.