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Tuesday, August 10, 2010
The Earth Bank: A Living Building System by Matt Brooke and Walter Cicack
The Earth Bank system has been successfully installed on the shipping container at the Eugene Federal Courthouse Garden. The final result was a concrete wall 3" thick supporting the living needs of various sedums. Time will reveal weather or not the Earth Bank can successfully allow seeds to germinate and thrive.
When we published our midterm post we had just finished our second round of test pours for the experimental Earth Bank mixture. As we were pouring our third round of experimental mixtures we had the idea to use the Earth Bank as a direct potting soil for starts and sedums rather than just seeds (as the project was originally conceived). This allowed us to increase the viability of the project by allowing it to support green life from the start. The seeds became a secondary feature intended to "fill out" the negative spaces left over by the sedums.
Our third round of test pours was highly refined with data collected from the first sixteen test blocks. In the third round we finally stumbled upon a mixture that seemed to be working- it was lite enough to be mounted on the shipping container, strong and stable enough not to fall apart and suitable as a living matrix for plant life. This is what our successful test block looked like:
As you can see we experimented with planting a variety of sedums and hearty native grasses in this test block. At the time this post was published, the block was nearly five weeks old and all of plants planted in it were still alive and thriving.
With a workable Earth Bank mixture selected, it was time for us to construct the mounting bracket and internal reinforcement for our living wall.
As the diagram above illustrates we designed the mounting system to be constructed of 1" wide x 1/8" thick strips of standard A36 steel and to be joined together using nuts and bolts rather than welding (because neither of us knew how to weld and the fabricator's estimate for the job was over $350). We acquired the steel from Coyote Steel here in Eugene and went to the EMU craft center to begin fabrication.
We drilled all the holes into the steel and then proceeded to fabricate the frame using a vice and hammer. The system was very simple as we had engineered it to have only 90 degree bends. Having bend and drilled all the steel to spec we then laid the frame out and bolted it together.
We had acquired a reinforcement screen mesh from Bring Recycling Center for a few dollars. We cut the screen to size and then installed it onto the frame using the nuts and bolts at the intersecting verticies and zip ties on the lengths.
We left the tails on the zip ties sticking up out of the frame as added horizontal reinforcement for the Earth Bank Mixture. We are glad we made this decision for reasons we will elucidate later. With the mounting and support frame constructed we took it out to the site and tested our mounting system on the shipping container to be certain that we had a workable mounting system.
Having drilled all the mounting holes and satisfied ourselves that the mounting system would work as engineered we set about building the formwork for the final pour of our Earth Bank wall. We went to the Lawrence woodshop to do this work. We constructed the formwork out of split 2x6s and a large piece of 1/4" thick plywood that was lying unused on the site.
With the mounting system and the formwork completed we took the project to the site to begin mixing and pouring the Earth Bank. We borrowed a cement mixer form UO Architecture Professor Stephen Duff which gave us a big advantage and made the whole job a lot easier.
Before pouring the mixture, we had to prep the formwork. We began by installing dozens of hemp threads through the formwork. the idea behind the hemp threads was that they would run through the width of the two layers of Earth Bank tying them together and to the mounting bracket.
We then needed to install some sort of form-release into the formwork. Recycled plastic grocery bags worked reasonably well when we did our test bricks, so we decided to use this method again. We installed the plastic bags into the formwork with a staple gun and then cut holes in the bags to allow the hemp twine to stick through.
We then began to mix the Earth Bank mixture in the electric cement tumbler and pouring the mixture into the formwork.
The formwork held a total of about 25 cubic feet of Earth Bank, but the cement mixer could only handle about 6 cubic feet at a time so we ended up pouring the layers of the Earth Bank in several stages. We had to work quickly however, because the Earth Bank mixture begins to dry and cure rather quickly and we needed it to still be wet when we were done so that we could plant into into.
After pouring the first slab of the Earth Bank wall we carefully scraped off all the excess in order to form a clean flat surface to lay the mounting frame on. We carefully pulled the hemp twine all the way through the first slab and laid them on the side of the formwork so that they could also be pulled through the second (top) layer of the slab.
With the first slab poured and prepped we carefully laid the mounting frame into the Earth Bank and pulled all the hemp twine through to the other side.
We then laid the top layer of the formwork over the bottom formwork and the mounting frame.
After three more rounds of mixing with the cement mixer and careful pouring, the top slab of the Earth Bank was prepped. We then pulled the hemp twine through the top slab and carefully set them aside. We did not scrape off the excess material of the top slab because we felt like a more rough, earthy look would be more aesthetically appropriate than a smooth flat surface.
Next, we quickly set about the busy work of planting our sedums into the top slab of the Earth Bank. We had collected about 30 lbs of various sedum species from our own back yards and those of our colleagues; we had several varieties, many of them in full flower.
The Earth Bank began to cure quickly and become cumbersome to dig and plant into so we recruited the help of some of our classmates on site to help us do the planting before the Earth Bank got too hard to manipulate by hand. With their help, we managed to have all the sedums planted into the Earth Bank within a half an hour, the job was done just as the Earth Bank was becoming painful to dig into. We chose to space the sedums apart by 2 or 3 inches in order to give plenty of space for our grass and wildflower seeds to germinate and grow. The idea with the plant spacing was that the sedums would provide an attractive living green aesthetic right from the start and the grasses and wildflowers would slowly grow into the negative spaces in between, the hope being that eventually the whole Earth Bank would be covered with vibrant living plants.
With the Earth Bank planted and prepared for drying, we placed some old scraps of plywood we found at the site over it to keep of excess sun and heat while the plants were in their most vulnerable state. Even with the data from the successful test block telling us that the sedums could withstand full sun during the curing process and pull through just fine, we wanted them to get a good opportunity to settle into the Earth Bank before exposing them to full sunlight.
The Earth Bank was allowed to sit and cure in this state for a week before we took any more action. The next thing we did was tilt the Earth Bank up into a vertical position and remove the plywood backing to the formwork in order to give the Earth Bank a good chance to cure thoroughly all the way through. We propped it up with some scraps of wood that we screwed into the side of the formwork to create makeshift knee-braces.
With the Earth Bank propped into an upright position and the plywood backing removed, we removed the plastic bag form release from the Earth Bank.
After allowing the earth Bank to continue curing in this position for another several days we were ready to mount it to the shipping container. In order to give it extra stability while being moved and mounted, we lashed the whole thing together with ratchet tie-downs to hold it firmly together.
The Earth Bank wall we had constructed ended up weighing several hundred pounds (including the Earth Bank material, the steel frame and the side formwork) and having a volume of approximately 25 cubic feet. We were unable even to budge it by ourselves so we requested the assistance of several of our colleagues and our professor. It ended up taking 8 people to get it off the ground and move it into position.
As our colleagues held it stable, we proceeded to mount the Earth Bank frame to the shipping container using standard 1/4" nuts, bolts and washers.
After installing all the bolts and removing the supports the Earth Bank held fast to the shipping container. We were relieved to find that the mounting system we had engineered was sufficient to do the job. We removed the formwork from the top and sides of the Earth Bank.
However, as we removed the formwork from the bottom of the Earth Bank we ran into an unforseen snag. The back slab of the Earth Bank was not adhering to the steel frame the way the front slab was. The rear slab was completely disconnected; our plan to use hemp twine to tie the two slabs to the steel frame was unsuccessful.
As you can see the rear slab was falling down, disconnected from the steel frame, the only thing preventing it from falling on the ground was the bottom feet of the steel frame. Since the rear slab was basically dead weight at this point we decided to remove it. Carefully breaking it apart with hammers and chisels we crumbled it down to a point where it could be slid in between the bottom steel feet and removed from the cage.
We ended up with a pile of wasted Earth Bank that had to be carted off and disposed of.
The front slab did adhere to the steel frame, however. We believe that this is probably due to two factors. First, the front slab had the benefit of the (highly textured) nylon zipties attaching directly to the slab and the steel frame. The zip ties can hold 50 lbs a piece and there were several dozen of them; this may provide some support to hold the slab onto the frame. The other factor may be that since the top slab was poured onto the steel frame and wire mesh it had a better opportunity to envelop and bond with the steel system. Either way, the top slab adhered strongly. In the end, instead of having an Earth Bank that was 6" thick, we ended up with one that was merely 3" thick. We found that this was a pleasing, thinline aesthetic and we were not disappointed with the final result. After all, the most important part of the Earth Bank was successfully mounted and installed.
Since the rear slab was no longer present to do the job, we decided to reinforce the adhesion of the front slab to the steel frame using a simple mortar mix applied directly to the wire mesh and the sectional pressure points of the steel frame.
The final installation of the Earth Bank appears as below.