This article first appeared in The Owner Builder 192 December 2015/ January 2016. www.theownerbuilder.com.au
By Maggi McKerron
Ten years ago I fell in love with a mountain. Mt Chiang Dao rises 2173 metres out of the forests of northern Thailand, its jungle covered peaks dressed in swirls of clouds. I leased a piece of land on a small hill facing the mountain. Under half a hectare, the land slopes down to a small rural Thai village under the mountain, clustered around the nationally famous Chiang Dao Cave.
Planning a B&B
I was approaching upper middle age and realised I needed to make some sort of plan for older age when my life might possibly slow down a little. This piece of land would be perfect for a B&B!
I did not have the money to develop the land, so I took off for the UK to make some. Although I am British, I was born in India and have always lived in Asia. Going to the UK to work was a challenging experience, as I had to learn to live in a western culture for the first time, at the age of 56.
While in the UK I took the opportunity to study natural building, beginning with an inspirational earthbag building workshop taught by Paulina Wojciechowska, author of the first book on earthbag building. Making a dome out of earthbags sold me on domes and round dwellings. I was determined to build round domes back in Thailand!
But using earth as the building material did not sit right with me. I am mildly asthmatic and need dry air and did not relish the thought of being enclosed in an earthen dome during six months of monsoon rains. I thought about rice husks. This is a product that no one wants. It takes ages to break down if added to compost, and is difficult to burn. It is also a desiccant, which means that it will draw moisture out of the atmosphere. Perfect!
After seven years in the UK I finally had enough money to return to Thailand. At least I hoped it was enough. There was no way I could calculate the costs of the buildings in any detail, as I did not really know how I was going to build my rice husk domes. I couldn’t find any information on the internet: no plans available, no books on building with rice husks. I worked out a financial guesstimate, which I finally reached in savings, and I bought a one way ticket back to Thailand.
My beautiful land was covered in towering brush and it was not until a team of machete wielding villagers cleared it that I discovered how steeply it sloped. What a challenge this was going to be!
I should mention here that where I was building, out in the scarcely populated countryside, planning permission, although preferred by the local council, was not an issue. In towns and cities I would have had to submit plans. My local council signed off the building after it was finished.
Beginning the build
Ready to begin my adventure, I posted on social media that I would welcome anyone who would like to help with the project, and people turned up. I hired some local day labourers from the village. We found the flattest area, at the top of the property, and one of the first steps was to prepare for a concrete base. I had been warned by locals that the termites were ferocious and there really was no alternative to concrete.
We marked out a circle 5.5 metres in diameter with some bamboo stakes. Then we got some tubing and filled it with water, and tried to find a level. No one believed what the water in the tubes was telling us, so I went and bought a spirit level. This confirmed the water’s message; there was still a big slope, even though compared with the rest of the land it looked practically flat. Leveling the area was our first task.
My very rough plan showed a concrete cap on the dome, as this was all I could think of to keep out the monsoon rain, so our next task was putting up six concrete posts to carry the weight of the concrete cap. Then the base of sub soil and stones went in, pounded flat
by enthusiastic volunteers, a trellis of bamboo for strengthening, a sheet of plastic as a damp proof membrane to stop moisture leaching upward, some sand and a final topping of concrete.
Now I needed to seriously consider the dome. I could not for the life of me work out how to construct it. Unlike earthbags, which are load bearing and could support a concrete cap, I was working with lightweight, not at all solid, bags of rice husks. I spent ages in hardware stores, second-hand wood shops and looking through books. I asked various local builders, but one after the other they shook their heads, mystified with the ideas of the crazy foreign lady.
At one point I decided to forget the dome and just build a hexagonal roof using the steel for conventional roof frames. One of the volunteers said: ‘But Maggi, your dream is a dome. You must follow your dream.’ So I thought again.
I found reinforced steel rods, rebar, bendable and long. I could buy quite thick pieces and long enough to go from one side of a dome to the other. First a piece of rebar was bent into a circle to go around the building, sitting on the top of the concrete posts. Then up went the rebar making the dome shape and we wired it onto the posts and horizontal rebar. Using different thicknesses of rebar and adding bamboo we made a dome shaped trellis.
The bamboo for the trellis in the dome came from bamboo poles we harvested from the land. These we cut and prepared and wove as needed. We used the same trellis idea for the walls, and our bags of rice husks would be attached to this frame. The whole thing looked like a giant bird cage!
The windows and doors were added as we built the bamboo trellis. This was complicated as the walls were going to be quite thick, so windows and doors needed frames to sit in. We learned as we went along. At no point in the building did we use any electrical tools – there was no electricity!
Rice husk walls
Filling in the walls came next. I found a place that sold second-hand polypropylene bags and had bought several hundred. Then I found a rice mill that agreed to fill the bags for me with their waste husks, 200 a week. These we had been collecting in preparation.
The first layer of bags was filled with gravel to guard against water and moisture damaging the walls, with a layer of sand on top of that, then the bags filled with rice husks. We experimented with different types of string, and different knots and found the method that worked best. They went up quickly and easily in a couple of days, and soon we were at the level where the curve of the dome began.
The bags were too big. They would be too unwieldy and heavy to attach. We had to empty them, refill them with less rice husks, then tie them up in the shape of a sausage. Our sausages were quite complicated to put up as we were attaching them to the inside of the dome to continue the inside line of the walls.
The dome looked wonderful! The next step was to put on the concrete cap. We used plastic sheet covered with chicken wire and put the concrete on top. We made deep overhangs to protect the walls.
The last step was the mud on the walls. It took a while to perfect our recipe as putting plaster on bags of rice husks is not the same as putting it onto earthbags or straw bales. The bags were not solid, so plaster had to be built up slowly in several layers until it was firm and strong. Then a final layer of lime plaster, followed by some decorations, and our dome was finished!
The big lesson I learned was never to put a concrete cap on a dome in the kind of climate found in Thailand. It cracked, and cracked again! But because the rice husks dry out so easily it has not caused any lasting problems. The second lesson was to attach the bags to the outside of the dome trellis. Much easier!
Three years have gone by since the beginning of the adventure. I have three domes and five roundhouses with thatched roofs. All the buildings with their thick walls of rice husks covered with earthen plaster are cool in summer and warm in winter. I have a beautiful home, made from three of the five metre roundhouses, joined by thatched walkways. My B&B is up and running. And every day and all day I can see my mountain. My dream has come true.
Maggi will be running a roundhouse building workshop in November 2017. See website for details: www.chiangdao-roundhouses.com
Links & resources
Sharing her adventures of living – and building – in Chiang Dao, northern Thailand.
Chiang Dao Roundhouses
Set on the side of a hill overlooking the spectacular Mt Chiang Dao, offering rice husk workshops and B&B accommodation.
For too long the insurance industry has held the owners of straw bale buildings captive while they sway back and forth with the prevailing winds when it comes to insuring our buildings. We begin to address this issue in the first of a series of articles on this topic.
By Kyle Holzhueter
Traditional Japanese earthen floors are called Tataki. The pronunciation is similar to the Japanese verb to pound, tataku, as these floors are pounded similar to traditional earthen floors in many other countries throughout the world. However, the word Tataki is written in Chinese characters as 三和土, meaning literally “three and earth” or “three harmony earth”, which reflects the fact that Japanese Tataki floors consist of three ingredients, earth, lime and bittern, a byprod the creation of a traditional earthen floor in Northern Japan as conducted by Keisuke Noda-san of Noda Plaster Works.
The floor is completed in stages. First, a 100-150mm layer of crushed gravel is compacted creating a stable and level base for the earthen floor.
Ink lines are snap to identify layers and the finish height.
The earthen floor is 100mm thick and consists of three layers. The three layers are applied, evened, pounded and compressed in the same day so there are no cold joints between layers. The number of laborers is adjusted to ensure that the entire floor can be completed in one day.
In Japan, the dimensions, techniques and tools used vary by region. In some areas, an 80mm earthen floor is applied in roughly two 40mm layers, or 50mm thick floor in two 25mm layers.
As mentioned above, Tataki consists of three ingredients: earth, lime and bittern.
Although the proportions depend on the qualities of the materials, the following proportions are a good place to start:
Sandy soil 100g
Hydrated lime 10g
In practice, aggregate may be added to balance clayey soils and the amount of lime depends on the size of aggregate and proportion of clay in the soil. A greater clay content will require more lime.
The following is the recipe developed by Keisuke Noda-san using entirely local materials in Hokkaido:
Clayey soil 1kg
Volcanic sand 3.5kg
Hydrated lime 150g
Calcium Chloride 150g
Red clayey soil 100g (for color)
When mixing, first the volcanic sand, dry powder clayey soil and hydrated lime are mixed dry. Because clayey soil and lime have a tendency to stick to mixers, the volcanic sand is added first. Next the clay is added and after that the lime. Lastly the red clay is added.
Separately, the calcium chloride is mixed with water, approximately 2g of calcium chloride to 1g of water. The calcium chloride will give off heat when mixed with water and care should be taken. When the calcium chloride is completely dissolved, the mixture is added to the dry ingredients. Because the finish mix is relatively dry, the dissolved calcium chloride should be added slowly and well dispersed in the mix.
The amount of water is very important for a number of reasons:
- To prevent cracking: If too much water is added, when the water evaporates, it induces shrinkage which could lead to cracking.
- To improve workability. If too little water is added, the mix will not compress sufficiently. The mix should form a solid ball when squeezed in one’s hand. However, if too much water is added, the entire mix becomes viscus, acting like a liquid, so that when one area is pounded downward another area rises.
Noda-san has developed a variety of tools for pounding.
Tataki specialty trowels consisting of thick honyaki steel produced by Yamanishi-san and available from Kiwado – Japanese Plastering. Heavy compression with regular trowels would cause the trowels to bend out of shape.
Simple lumber and hammer: next to walls and other difficult to reach areas, a metal hammer can be used to hit a narrow piece of lumber, which will compact the earth under the lumber.
To construct one layer, roughly 50mm of material is spread evenly on the floor. Screeds and guides can ensure the mix is applied evenly.
The 50mm of material is then pounded and compressed to 30-33mm.
Again, special care must be taken where the floor meets walls or difficult to reach areas to ensure proper compression.
A network of Iguasa rushes is sandwiched between layers. This helps prevent large vertical cracking.
The same process is repeated for the second and third layers.
After the third layer has been completely compacted, the final finish can be decided. There are several options:
- For a more rustic, traditional appearance, leave the floor with an open pour finish. This finish hides future scratches and wears and tears. Regularly watering and sweeping the floor results in the “cement-like” earthen floors found throughout the world.
- Immediately after completing the third layer, mist or lightly water the surface of the floor and compress the surface. Additional material can be added in depressions to create a flat surface. The compressed finish results in a harder surface more water and abrasion resistant. This floor is quite comfortable barefoot. Although future scratches and wear and tear will be more prominent, these areas can be re-wet and compressed again.
The area of the wall which meets the floor is cleaned with a wet brush to create clean lines.
After compression, the floor is protected for approximately one month.
In this case, to ensure slow and even drying, the floor is covered with loose straw and then straw mats.
Lastly, a dilution of bittern is sprinkled over the straw mats.
In cases where the floor must be walked on immediately, protective flooring can be used as seen in the photo above.
Many thanks to Keisuke Noda-san of Noda Plaster Works for sharing his experience and knowledge.
Kyle works as a builder, consultant, researcher and educator specializing in natural building materials such as straw bale, light straw clay and natural plasters. He has a PhD in Bioresource Sciences from Nihon University where he researched the hygrothermal environment of straw bale walls in Japan and building practices to control moisture. Apart from academia, Kyle has studied natural farming in Japan, permaculture in Australia, and organic and biodynamic farming in the US. Further details can be found at the following links: http://holzhueter.blogspot.com http://japaneseplastering.blogspot.com
In the first of a two part series article, Jacob Deva Racusin explains the differences in monitors for your walls. This is “must know” information for every builder and owner.
We review the first comprehensive how-to guide covering the topic of earthen floors. Find out why you should have it in your natural building library.
Alex Sparrow begins a two-part series on hemp lime, or hempcrete. Hemp lime is relatively new but is fast becoming part of the natural building lexicon.