posted 7 years ago
Your site sounds like a dream come true to me. The slope and soil type are both a challenge and the perfect situation for rammed earth using anywhere from 5% to 10% portland cement depending on the exact needs of the soil. You'll need something to act as the forms x 2 ( if you can get 2x12 by 12ft and good stakes), a roll or two of galvanized wire ( thin single strand is good ), shovels, a place to mix the fill ( a 50 gal drum would be fine), a few tampers ( heavy metal plate that sits flat on the ground with a stick pointing up as a handle ), a strong back, or many strong backs, and a length of clear tubing as long as your longest horizontal dimension plus about 4 ft ( 1m ).
Quick and easy rammed earth:
Dig a trench as deep as convenient running straight down the slope and at least a foot wide (1/3m), setting the dug out material in a neat row/mound beside the trench. Set the forms inline with the sides of the trench, stake them in place and block the ends; don't worry about leveling at this point. At 3ft (1m) intervals, drill two holes about 2inches apart on opposite sides of the form top and bottom ( on the bottom, make the holes about 5 inches from the edge so that they will have enough room for the stub wall below the wire for the second run); run a length of the galvanized wire through both the holes from one side of the form to the other and twist it tight. In your mixing container put in 9 shovels full of soil, one shovel full of portland cement then blend it, repeat until the mixing container is about half full. If your soil isn't the least bit moist you will need to add minimum amounts of water for each group of 10 shovels full, but only enough to make it damp. You are going to need a lot more soil than what you pulled out of the trench so plan on where to excavate (for example, where you are going to put your septic system or your cistern). Place the mix 4 to 6 inches deep into the trench/form and tamp well being careful around the wires. Repeat until the mix is tamped to the top of the form. Set up the second form, remove the blocking from the end between the two form sections and repeat. Remove the first section's form by first clipping the galvanized wires on the outside of the forms. The wall should be quite stiff by now so you can move the form to the other end of the second section. Once you have the first trench done do a second 6ft (2m) to 9ft (3m) to either side and repeat. They don't necessarily need to be parallel but it helps later if everything is square.
Now you have stub walls to attach the forms to for the second row up and the following ( the reason that the holes for the wires are 5" in from the bottom on the bottom side of the form, so the new layer can be attached directly to the wall below). From this second row on, make the form's top level using the clear tubing filled with water except for the last 4 inches on each side as a level, and proceed, stair stepping them if necessary due to the slope. When you have the wall high enough for the foundation block out sections inside the forms at appropriate intervals for floor joists/supports. Side walls inline with the trenches can be continued up, but you don't want the uphill or downhill end walls in contact with the soil so that water can freely move down the hill below the house. The floor must be made water / vapor proof so that moisture does not penetrate from below.
Once you get a platform built on top of your structure, I'd put up a yurt. They are stable even in high winds due to the round shape with little for the wind to push against, weather resistant, and very versatile. If you keep the structure low enough the wind shouldn't be able to lift it. If you decide to take the walls up higher than about 6 feet (2m) you must start to think about footings for the structure as they are what resist lifting due to wind loads. Standard footing tables are available online.
Your volcanic ash soil is the absolute best for rammed earth because of the shape of the particles. They will lock together perfectly and never degrade. With the addition of the portland cement they will last centuries. if you have stones in the area you can use them as fill known as rubble to reduce the amount of soil required.