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Earthship Walls

Creating an earthship wall is simple. There are basically two types of walls in an earthship: the outer tire walls and the room separating inner can walls. The tire walls do have a stack of cans on top that ranges from one to three feet to the ceiling. Most can walls will have some pattern of coloured bottles. The bottles could be in a straight line or any artistic pattern that the home owner desires. During our internship on the Buffalo earthship we mostly worked on walls at different stages of being finished. Some detailed notes about earthship wall finishing are outlined below.

The primary components of wall finishing are Portland cement, sand, and water. Depending on what stage of wall finishing you are on determines the thickness of the material. Filling in pockets and spaces to make the wall flat requires thicker material, called mud.

Cement, Sand, and Water.
Cement, Sand, and Water are the Only Things Needed to Finish an Earthship Wall.

They can be mixed by hand. However, an electric or gas powered mixer makes the job go much faster.

Cement Mixer.
Electric Cement Mixer Running Off the Newly Installed Solar PV System.

Once a load of "mud" has arrived at your work area, you can begin applying the material to your assigned wall.

Earthship Wall Types

  • Can Walls

    The Inner Can Wall

    To build a can wall requires many loads of mud (mortar) and cans. The basic recipe for mud is 2 five gallon buckets of sand, one half bag of 92 pound Portland cement, and a half of a five gallon bucket of water. The water is poured first to clean the mixer from the previous load build up. Then you toss in the two buckets of sand, followed by the half bag of cement. Be sure to knock off extra build up material from the blades of the mixer.

    When building the wall, you first wet the work area, then lay down several inches of mud, then you pinch a can to make one side pointy, and stab it into the wet mix. Lay the next can at least two fingers away from the previous one. The trick is to lay the mix down uncompressed; otherwise the material fall apart when the can is pressed in. The can acts as a compressing mechanism. It secures the can as well as presses the material in place, and this action removes air pockets in the wall.

    Earthship Can Wall.
    Earthship Can Wall

    The cans in an inner wall should alternate so that some cans' opening will point your direction, while others will point to the room on the other side of the wall. The can pull tab acts as a catch when applying later layers of plaster, therefore, the tabs should be left on the cans. The open side of cans stacked in outer walls should always point outward. Likewise, cans used to fill spaces between tires should point downward. This prevents moisture and mold build-up in the cans.

    The cans should stack in a flat plane. If there are any bulges or valleys in the can wall, because of misalignment, they must be filled with extra mortar to make the wall flat. You should use a level to make sure your cans are lined up correctly.

    Another important point is when your cans meet an object behind the wall, the cans should be scrunched to keep the wall in alignment. For example, if near the top of your wall, you are close to a ceiling viga (roof supporting log), then you'll need to make the cans smaller to fit in the same plane. It is not advised to cut the cans, as that will weaken them. Having a rim on both ends of the can makes them strong.

    Before building your can wall to the ceiling, you'll want to create a Porcupine line in the ceiling with nails or screws. This will give the cement something to grab onto when you finish the can wall. Stack the cans and mortar as high as you can in the wall before the ceiling. The final step of completing the inner can wall is to pack mud on top of the cans until it reaches the porcupine line in the ceiling. At the end of each work day, all tools, buckets, gloves, and floor should be cleaned of excess mud. Once the mud dries, it is very difficult to remove.

    The Top of an Earthship Can Wall.
    Top of an Earthship Can Wall

    The Top of an Earthship Can Wall.
    Top of an Earthship Can Wall

    The Outer Can Wall

    Once the inner can wall is finished, you should see a matrix of stacked cans to the ceiling. You can then begin covering the cans with plaster. Plaster here is defined as the same material you have been using all along, but it is a bit thinner and uses a finer grade of sand. It is applied, not by hand, but by trowel and tray. The trowel is about 14 inches (42 cm) long and 4 inches (12 cm) wide, with a handle. The tray is a flat piece of metal that is one square foot and has a handle attached to the bottom middle of the tray.

    Wet your wall down before applying plaster. Then, you scoop a tray of material with the trowel and head towards your wall. You'll want to always scoop the heavy wet material with the bottom of the trowel, not the top. Repeatedly using top to scoop will eventually break the handle away from the trowel blade.

    With the plaster on the tray, you head to an open spot in your wall and push as much plaster as possible upward onto the wall. Its a little bit tricky to get the material to stay on the wall the first time. Much of it may fall to the floor. There are several things you can do minimize losses and get the plaster to stay on the wall. Firstly, you only want to apply thin coats at a time. So, estimate how much material you need to cover an area, then push the plaster on to the wall as high as you can go. The thinner the application, the lighter, and more likely it is to stay in place. Secondly, do it fast. At first, it is difficult to push the heavy material onto the wall, because you have been carrying buckets of sand for the last few days and you are tired. It will take several tries and maybe a couple nights rest before you can go faster. Thirdly, as you push the plaster up the wall, wiggle the trowel from side to side. It helps the material stick better.

    Applying Plaster to a Can Wall.
    Applying Plaster to a Can Wall.

    You'll want to push several trays onto the wall quickly, covering about one square meter. Then you can go back and smooth the area out. Your objective here is to make the area as flat as possible using the trowel. Rub high spots to low spots, making that section of the wall nice and even. Before going on to the next section of wall, take a fork or small rake and scratch lines in the newly applied plaster. This will help the next layer adhere better. Once you have completed the first layer of plaster some cans may still be showing. Those will be covered in the next layer. Continue applying layers until the wall is nice and smooth and you have a quarter inch (1cm) clearance around your door edges and bottles. The final layer of plaster, you can scratch or rub with a sponge to make the surface gritty for application of the final coating of white material.

    The edges of your can wall that butt against other materials such as wood should have attached a layer of metal mesh called lath. The lath is a mesh material that has diamond shaped openings where the edges of the diamond are angled upward. This helps hold the plaster material to the wall. Lath is necessary when plastering near other materials because as the wood dries out it changes shrinks. If the lath is not used the plaster will crack or a gap will be left between the plaster and wood. Screwing the lath to the cans requires some technique. You'll want to make sure the lath is tied down to the can securely. The achieve this make sure the threads of the screw stop at the edge of the can. If the screw is longer than the width of the can, punch it through to the other side of the can, so that the screw is penetrating both sides of the can. Try to select the bottom edge of the can if possible.

    Securing Lath Material to Cans
    When Securing Lath Material to Cans Try to Screw Into the Bottom Edge of the Can.

    Your finished can wall should almost as smooth as dry wall in a conventional house. There will be minor hills and valleys in the can wall, so don't spend an eternity trying to get it perfect. Make sure your tools are clean after every work session.

    Plaster Completed Can Wall.
    Plaster Completed Can Wall

  • Tire Walls

    When completing a tire wall, there are large spaces between the tires that must be filled. Using soda cans along with mud reduces the amount of Portland cement needed to fill the large areas. You slap mud into the v-shaped spaces with your hands and then work it in until it sticks to the tires. You don't need to fill the space in one try. Press in one edge pointed can, apply more mud to cover it, then press two more cans over that. You are trying to bring the crevices to the surfaces of the tire edges so that the tire wall will be as flat as possible. This will take several applications. Don't forget to scratch each application of mud, so that the next layer will stick easier.

    Mud for Pack Out.
    Mud for Packing Out a Tire Wall

  • Can and Tire Walls

  • Other Wall Types

Steps to Finishing Earthship Walls

  • Stacking Cans

  • Pack Out

  • Plastering the Finishing Layers

  • Final Coat

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Tags: Earthships, Alternative Building Materials, Tire Walls, Portland Cement, Recycled Cans, Off-grid Living, Thermal Mass, Greenhouse, Grey Water, Black Water, Ventilation, Cistern, Solar Panels, Rainwater Catchment

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