We are in the process of building our out-building. Yesterday we put in our beaten earth floor. Here is how one is made the Japanese way. I guess that some places use ox blood in it. We did nothing that extraordinary.
We have an area about 50 square meters for which we wanted a floor to store our small tractor, other farm implements, and harvest through the winter. We have chosen to build as close to a traditional Japanese "kura" as our time and effort will allow. That means that instead of a tile roof with dirt underneath as an insulator, we are using galvanized metal with a foam insulator underneath. And instead of two layers of bamboo lattice in the walls, we will use one layer of lattice, making the walls about half as thick as the 40cm walls on the real deal. Yesterday we put in the beaten earth floor, it was quite a workout, but made considerably easier to do with experienced help and modern equipment.
We started by digging a 30cm wide and about 10cm deep ditch 30cm from the where the wall will start. The ditch will serve as a deep spot to keep the floor from slipping outward. There is also a ramp area in front of the door that will be kept relatively dry with the overhang on the front of the building, for which we dug a deeper ditch, about 30cm deep. We put a wooden frame around the building, just within the ditch. Then we started mixing earth and plaster. We used about three quarters alluvial sand to one quarter plaster with a small backhoe. We mixed a total of about 5 metric tons of earth, and started from the outside, shoveling in the sand and beating it down with hardwood mallets. They were short handled, and the business end was long and rounded. The entire mallet was about 50cm long, and the striking surface was about 30cm of that. We were working on building up about 15cm of beaten flooring, which required about three layers of earth. My guess is that loose earth compresses to about 1/3 of its original depth after beating. The outside floor required hand tamping, because it was laid around the beams of the building and inside the wooden frame. We used two gasoline powered tampers to compress the larger areas inside. The outside floor was nicely polished with a mason's trowel. One of the masons there to help us with the project kindly showed me the method for flattening and smoothing the surface. You must beat it to smooth out the bumps, and then sort of massage it with the trowel. This works the larger particles of sand in and brings the finer particles out, which smooths the floor.
We started working on the floor at around 8 in the morning and finished cleaning up and loading the equipment back on the trucks at around 6. Several of our friends came to help, and were happy to have had the experience. They are also working on developing their homesteads, and one family that came to help is in the process of building their own home with wood working studio and extra sleeping areas to come. I'm sure we will use our hard-earned experience with their projects, too.
It was hard work, and I am sore today from swinging those mallets, but we enjoyed the work and companionship, and now we have an earthen floor that will return to the earth, hopefully long after I have.
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