Rapidobe is a form of construction of our own devising. The idea comes from the simplicity of earthbags, but made faster, cheaper and easier. You can use any dirt, even if it has rocks in it, making it a great option for almost any terrain.
This method can be used for walls, or for holding back dirt in an underground construction or retaining wall.
For a foundation, dig a trench and fill with gravel or rubble. Its width needs to be wider by a few inches on either side than your wall will be. The fact that you do not need a concrete foundation is one of the reasons that makes this method so cheap.
Place posts every two or three feet on either side of your wall. You want the posts of one side of the wall to be directly opposite the posts on the other side of the wall. Make sure the posts are not leaning outwards. They can however lean in towards each other a little.
We have used metal pipes as posts as well as Juniper limbs. The advantage with the metal is that you can hammer them into the ground quickly. Tree limbs are much cheaper (in our case free), but you have to dig a hole for them. With short retaining walls that are only a couple of feet tall, you can use rebar - cheap and easy to pound into the ground.
The type of post you use is not that important, so pick one that suits your purposes: cheap, easy, decorative.
Tie a C-purlin or suitable bondbeam material to the outside line of posts [the first time we did this, we put the bond beam on the inside of the posts, and learned that the outside would have been better]. Tie it at each post. You can also use a self-tapping metal screw at each post to hold everything in place. It needs to be just above the top of the posts. Make sure that it is level.
The rafters of your roof will be attached to this bond beam.
- Cut a fabric like hail screen or stucco mesh for the length of your wall. The width will want to be the sum of the height of the wall x2, its width, and an extra couple of feet, forming a U-shaped bag inside your posts. If you are doing a retaining wall, the bag only needs to be L-shaped. The hail screen will make the stucco easier.
- Place the hail screen inside the posts, with the extra couple of feet hanging down on the outside of the wall.
- Do the same with a vinyl tarp. Scrap billboard tarps can usually be found for cheap or free in most cities. They are very strong and work well for this application.
- With steel wire or other strong metal, tie the posts of one side of the wall to its counterpart in the other side of the wall, just below the bond beam. You can make the top of the wall thinner than the base if you wish.
- At the ends of the wall, fold the fabric in on itself, like the end of a package. Using wire, tie the end posts together along several points down the post. Allow for a bulge on the end of the wall so that the posts don't get pushed outwards. This will be sufficient to close the bag on the ends.
- Using any dirt that is available to you, start filling the bag.
- Make sure you tamp the dirt firmly every so often, so that it is well compacted.
- Once you reach the top of the posts and have compacted that final layer, fold the excess of both fabrics over each other and tie them securely together.
You will not need to stucco immediately, as the vinyl tarp is waterproof. However, it will eventually break down in the sun, so make sure you get around to before that happens. The vinyl should last at least six months in the sun.
On the inside, you can use any plaster, as it does not need to be waterproof. We use a gypsum plaster. This is cheap and easy. Just add water to the powder and apply with a trowel. Be aware that it dries very fast, so you only want to mix up what you can quickly stucco. Mix it to the consistently of gloopy paint. If you want to put on more than one coat, you can mix the second coat wetter and apply with a brush. It is very sticky, so goes on easily, but when it dries it is exceptionally hard. You can then paint it.
On the outside, a concrete stucco is better. You want to use acrylic in your mix, as that will adhere far easier to the hail screen. We mix the first coat with just cement and acrylic and paint it on with a brush. The second coat, add sifted sand. You can put it on with a trowel, or keep the mix a little wetter and paint it on. The final coat can be with or without sand, depending on the finish you wish. Paint with a waterproofing paint and then a regular outside paint.
Depending on how tall the wall will be, you may want to add buttresses. These will help support the weight of the wall. You can make these buttresses into a feature, like a bench or archway for added beauty.
If you want to avoid the need for buttresses, you can make your wall curvy, which is much stronger than a straight wall. You can also make the wall shorter. To do this, you should build into a hill. Start off with a short wall on the ground, a few feet tall, and back fill with dirt. Then you start another wall a couple of feet back, and up the hill a little. This will give you a natural shelf inside the house.
We really liked this method of building. We put a 35 feet wall up in two days with three people, excluding the stucco and plaster. It was also very cheap. We do not yet know the durability of this method, as we are the first that we know of to have used it. Time will tell, but it certainly seems very sturdy and has not shifted at all in the six months it has been standing.