Earthbag Building utilizes the ancient technique of rammed earth in conjunction with woven bags and tubes as a flexible form. The procedure is simple ; The bags are filled on the wall using a suitable pre-moistened earth laid in a mason style running bond. After the bag has been laid, it is thoroughly compacted with hand tampers. Two strands of 4-point barbed wire are laid in between every row,which act as a “vel- cro mortar”cinching the bags in place. This provides exceptional tensile strength while allowing the rows to be stepped in to create corbelled domes and other unusual shapes.
STAGE 1: BAG TESTING
1. Equipment/ Materials:
– Polypropylene bags – Buckets and cans: sizes (500gr, 2kg, 4kg & 10kg)
– Cement (or lime) – Barbed wire
– Level – Pick axe
– Steel plate – Wooden sticks
– Water – Shovel
– Measuring tape – Gloves
– Pliers – Nails (2 inches)
2. In the making ; Tools.
– (DIY) Bag stand:
A stand is needed to make easier the bag filling process. To be sure that the stand support the charges of the bag full, it’s better to make it with strong wood or even with steel. It will also helps to control the filling of the bag (no fat bags are allowed!). We tried the simple one with wood sticks. Unfortunately ours didn’t last long… Tip: Make sure you choose a strong material to fabricate them.
– (DIY) Tamping devices
Fist we tried flopping the bags every way possible, stomping on them and also banging them with various tamping devices. We fabricated two tamping devices with buckets, cement, barbed wire and wood sticks . One was used to tamp the soil inside the bag and the other one to tamper the bag once on the ground.
3. Preparing the earth…
Clay plays the leading role in the performance of any traditional earthen wall building mix. We used a simple test layman method for determining the clay to sand ratio of a potential soil mix.
First of all we excabated and prepared the site, later we tested the soil and added water in order to get an stable quality clay that could be molded with the minimal cracking. For a perfect mixture the soil has to contain: 30% clay, 70% sand and 10% water to get a plasticity. Once on site, we calculated with the tools we had that for a bucket of 10kg soil, 4 buckets of 500gr water are needed.
4. Filling the bags
1- Place the bag in the stand – Fill the bag with the buckets of mixed soil- Place the bag.
After each filling make sure to tamp the bottom of the bag, so no empty space remains (pay specially atention to the corners). Simultaneously, make sure the bag doesn’t go fat at the bottom. Keep on filling until the bag is almost full, next remove the stand and close the bag. To close the bag fold each bag shut like an envelope and pin it closed with a nail on each side.
Lay the bags on the ground and tamp them thoroughly with a full pounder making sure that it is not too tight thus the soil can expand .
Start the second bag one bag’s length from the first bag. Continue filling until the dirt is 15 cm from the top of the bag. Remove the bag stand and firmly press the soil. Fold and lower the folded end into the top end of the first bag. This will hold it shut without pinning. Place the bag firmly up against the bottom of the previous bag. The same procedure is done for all bags.
When all the bags of the row are placed, they are ready to be tamped. First tamping down the center of the whole row. This forces the shoulders of the bags together to prevent shifting. After the whole row is first tamped down the center, then tamp from the center of the bags towards the outside. Continue to tamp the whole row until the sound changes from a “thud” to a “smack”. Make sure that once tamped, they are leveled and lined.
– Adding rows :
Before starting the second row, two strands of 4-point barbed wire are laid in between every row, which act as a “vel- cro mortar”cinching the bags in place. This provides exceptional tensile strength while allowing the rows to be stepped in to create corbelled domes and other unusual shapes
we made use of stones to help holding the wire down as you lay it. Usually the barbed wire stands on a dispenser conveniently located at one end of the wall. After the barbed wire is laid, a slider is placed under the bag stand. The steel plate aids in maneuvering the bag easily on top of the wire. Fill and fold the first bag shorter than the one underneath to create an overlapping joints. Once filled, adjust according to your particular conditions, then remove the slider. Repeat the same procedure as in the first row, placing the slider under each bag being filled. Always install each bag firmly against the previous bag to create a tight, vertical seam. In order to maintain a wall that doesn’t lean in or out, check the vertical surface with a level after each row is installed.
– Natural plaster: soil + cow dun + ashes + water –> one bucket of 10 kg each
For our test we tried only one layer, but usually the plaster contains 3 layers:
1° Only soil and water
2° The whole mixture soil-cow dun-ashes-water
3° The final layer is only with cow dun and ashes mixed with a bit of water
Those three layers are necessary to prevent cracks in the plaster. Indeed after making our plaster, once it was dried, we immediately noticed cracks in it. Usually Masai wait between 6 months up to 1 year to add an extra layer, always according to the state of the plaster.
– Cement or lime plaster:
cement/lime + sand + water –> 1 bag cement + 16 buckets sand + 8 buckets water
To fix plaster to the bags we will use chicken wire . This one is fixed with binding wireknotted on the barbed wire in every row, or with extra nails to be sure that it’s tight to the bags.
One of the main issues found with Cement plaster is that it uses a lot of bags of cement and water, so it increases the construction budget. The issue with the natural plaster is that it can be washed away by the rain or any kind of erosion, so it needs a renovation every year or anytime depending on the quality of the plaster.
As an alternative we could use both kind of plasters, using the natural one as the inside plaster, and the cement/lime for the exterior facade to prevent erosion.