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Tataki: Japanese Traditional Earthen Floor

By Asia, Floors, Issue 67, Japan, Regional No Comments

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.

The Mix

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

Bittern 1g

Calcium Chloride

Calcium Chloride

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.

Calcium Chloride diluted in water

Calcium Chloride diluted in water

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:

  1. To prevent cracking: If too much water is added, when the water evaporates, it induces shrinkage which could lead to cracking.
  2. 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.

Tools

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.

Application

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.

Iguasa Rushes for reinforcement

Iguasa Rushes for reinforcement

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:

  1. 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.
  1. 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.

The finished Floor

The finished Floor

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

Traditional and Contemporary Natural Building in Korea

By Bales, Design, Energy, Floors, Issue 62, Plaster, Straw Bale Construction, Straw-Clay, Walls No Comments

By Kyle Holzhueter

Editors Note – This article is a feature length pictorial look at the various aspects of natural building in Korea.  The full-length article will be in the upcoming issue of The Last Straw and is available in its entirety right here on the website for subscribers.  Make sure you have a subscription soon so you won’t miss this stunning array of natural building techniques.

Traditional Korean Architecture

Traditional Building in Korea relied primarily on natural and local materials.  Buildings were traditionally designed according to the 間 (Korean: ka, Japanese: ken) module, a common measurement found in east Asia.

East Asian Modual

East Asian Module

Traditional Korean homes generally have a timber frame with adobe or wattle and daub infill, though regional variations are found throughout the country.

Traditional House

Traditional House

Regional Variation

Regional Variation

Especially on Jeju Island where volcanic rock and strong winds are abundant, homes traditionally consisted of a double wall system with an exterior wall of volcanic rock surrounding an interior wall, creating a protected corridor around the house.  This in turn, protected the interior walls from wind and rain and improved the thermal performance of the home.  Also because of the strong winds, thatched roofs were generally secured by a net of straw ropes.

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Earth Floor – TLS #52

By Floors, Foundations No Comments

This article was originally printed in Issue #52, 2005

by Tom Lander – New Mexico, USA

dirt1We have by no means mastered Earthen floors but have gained enough experience to have been hired this past building season to install two, adding to the ten we have worked on along with teaching another dozen or so here at LanderLand during our workshops.

Our current style is some times called a poured adobe floor. The term poured seems to come from the world of concrete floors but a better word might be placing. No matter what term or method, one needs to properly prepare the sub floor. We prep to within of 1/2 in./13mm of finished grade and then basically apply the final 1/2 in./13mm topcoat. Like any earthen application, one needs to know their material in regard to the clay content of the soil. Here in Kingston, New Mexico, our soil has close to a 30% clay content so it’s a dream to use.

We teach two mixes for floors, what we call our sand mix and the other a straw mix. The sand mix is made up of 1 part sifted clay soil and 4 parts course fill sand with the largest particles as large as 3/16 in./5mm. These large particle sizes mixed with finer aggregates keep the floor from shrinking, cracking, and add compaction strength, and are also easier to apply. The clay soil is more like the binder and filler. You need enough water to mix damp. You can add a small amount of 1/2 in./13mm chopped straw for the aesthetics but it’s not necessary.

Our straw mix is a variation of our basic earth plaster with added sand. 2 parts sifted clay soil, 2 1/2 parts course fill sand and 2 parts 1/2 in./13mm chopped straw. Start with 1 part water. This mix is harder to apply than the sand mix. The wetter the mixes the easier they are to apply but the moisture may cause shrinking and cracking.

Prep Work

Let’s move away from the mixes and talk a bit about prep work. The heart of a good strong crack-free earth floor is the base that it is applied on. This is true for almost any floor be it concrete, tile or wood. Earth floors are more like concrete in that they must be properly compacted, graded and screeded flat. For the inexperienced owner/builder, floor prep can be intimidating, again the compacted sub floor is the key.

Apply your fill materials in “lifts” of 1 in./25mm to 2 in./50mm and compact damp. A trick, if you have the time, is to flood these materials with the garden hose. You can rent noisy, smelly plate and foot compacters; some big floor jobs require this. I still would buy an 8 in. x 8 in./20cm x 20cm hand compactor. I’ve moved away from making a compactor from a steel pipe and welded plate or a coffee can filled with concrete. I recommend prepping your floor early in the building process so it has time to be compacted naturally from working on it; this also keeps your walls clean, assuming your floor is last in the construction process.

In addition to compacting, there are also possible moisture issues and, in some locations, soil gases like radon. These are issues you or the builder will need to address. Certainly it is difficult to write about floor prep and “build up” in a short article. There are so many variations and situations depending on your particular site and needs. I always recommend reading about conventional building materials and techniques and talking with builders in the area.

I’m a big fan of radiant heat and almost always add the pipe to my concrete slabs even if I am not going to heat the slab. Never know when someone might. Pex pipe is easiest with concrete slabs, the most efficient being an isolated slab where 1 in./25mm or 2 in./50mm foam lines the bottom and sides, (a thermal break) steel mesh is laid down and the pipe attached with zip ties. On small floors, I now use cattle panel fencing for my wire mesh rather then the traditional rolled mesh; it’s more expensive but for me so much easier to use. So, in my opinion, the best floor would be a 4 in./10cm thick, 3000 psi concrete slab with added fiber and PEX radiant heat pipe with a final 1/2 in./13mm earth top. Don’t forget your fly ash and control joints, concrete cracks. This of course is a mix of conventional and natural, not for the purest.

One 300 sf radiant earth floor we did had 9 in./230mm of pumice put down over the native rock soil as the insulated layer and then we brought in another 10 in./250mm of crusher fines (road base), sand, earth, no foam and no steel. This technique had it’s own challenges, where again experience and creativity help. What is interesting in this house is to notice the different “feel” to the radiant floors from the earthen side next to the conventional isolated foam 4 in./10cm concrete radiant floor in the adjacent room. They both work, the house is warm but the concrete feels hotter to the feet.

Installation

So now you have prepped your floor rock solid (like concrete, huh?) to within 1/2 in./13mm of finish height. You have also gone around all the walls and drawn a line at your finished height. A day or two in advance, you might need to go around and fill any holes, voids or low spots with a damp clay-sand mix, maybe even tamping a bit with your nice tamper. When dry you should be able to sweep up any loose debris.

It’s a good idea to mix up your material a day in advance. Now, do your math. Calculate your square footage then your cubic footage and add about 30%. If your room is 10 ft x 12 ft, then 10 ft x 12 ft equals 120 sf. Multiply this by 0.0416 to get cubic feet. (0.0416 is 1/24th of 12 in.) 120 x 0.0416 = 4.99 cubic feet.

[ For metric calculation: 3m x 3.6m = 10.8m2. 10.8m2 x 13mm = 0.14m3]

Add 30% more material. 4.99 x 0.3 = 1.49 for a total of 6 1/2 cubic feet. We add 30 % due to the fact that we will be measuring our materials dry so there is air space. Once wetted and applied, the material gets compacted by the toweling process and we lose volume. You will need a container to store all this material. A simple tub can be made out of a frame of straw bales set on the ground and lined with plastic or a tarp. You can also buy large kids’ swimming pools. The color of your floor will be the color of your dried clay. You can add concrete liquid or powdered colorants. It is always a good idea to do a few 3 ft x 3ft.90cm x 90cm samples to test for shrink, cracking and color, also a good way to practice your applying techniques.

How to apply

Again one of those concepts that is best shown during a workshop training session than through trying to write about it, but here it goes. Ahead of time make up a few 1/2 in. x 1/2 in./13mm x 13mm screed sticks. These are also the thickness guides, four per person. Vary the lengths, 12 in. to 36 in./30cm to 90cm. Also make some wooden pool trowels out of the 1/2 in./13mm thick concrete wood floats from your building center; they cost around $3.00 USD each. Keep one square for corners.

Plan your route of attack so you will be able to work your way out of the room. Begin by setting down some pre-wetted wood sticks – trowel lengths apart, shovel down some material and start working in the material between the sticks. The trick is to make sure the material is compacted well, no voids. Do a few square feet leaving the sticks in place to run your trowel over thus establishing the thickness. Don’t spend a lot of time making it look good right now. Slide out the sticks, you now have a square groove that needs to be filled. First, take your trowel and press the sharp sides and ends down to form sort of a vee, now add small amounts of material in the vee and trowel it flat. Any voids or air pockets will leave a spot for cracking so compress well. The tendency is to put too much material in at one time; instead use a small amount frequently rather than large amounts all at once. Keep your guide sticks clean, wash frequently so as not to add buildup creating a thicker and uneven floor. As you progress along placing material and removing sticks, go back over the previous areas with your trowel to smooth and even out your floor as far as you can reach back over what you did. Sounds easy? Hopefully you worked this all out in your 3 ft x 3 ft (90cm x 90cm) test samples.

Sure looks good doesn’t it? You’re not done yet. More steps involved as the floor begins to dry. A word of caution about drying, it’s important to get even drying. If the sun shines in a window or door, these must be covered up. Air circulation helps to remove the moisture and speed up drying but again you need even flow.

Hard Troweling

Now it’s all about timing. On hot days/in hot climates, we find it best to apply the floor early in the morning so that hopefully by late afternoon or early evening we will be able to get back on the floor with kneeboards and steel pool trowels, or apply late in the day and hopefully you are back on it first thing in the morning. Miss this window of opportunity and your floor will be too hard to steel trowel. If you were so good applying the material with the wood floats and you are happy with the results, then one can skip hard troweling so your floor will be a little more course.

So your floor is drying, time to hard trowel on kneeboards – 3/4 in./20mm plywood, 18 in. to 24 in./45-60cm square or 2 in./50mm foam blue board works well. Make sure to wet your kneeboards, otherwise they stick and pull up your material. Almost like hard troweling a concrete slab. Steel troweling tightens up and flattens the surface. We use pool trowels and basically just go over the whole floor again, pushing hard with two hands in big sweeping motions.

Once your floor has completely dried, it’s time to seal and fill the floor with Linseed oil. We will address sealing in our next article.

Tom and Satomi Lander have been involved with natural building since 1993 and began teaching straw-bale building and earth plaster in 2003.

They can be reached at <[email protected]> www.LanderLand.com

Visit www.LanderLand.com for color images and earthen floor workshop information.

Sealing an Earth Floor – TLS # 55

By Floors, Technical One Comment

dirtThis is the second of a two-part article on creating a poured adobe or earth floor. See Earth Floor, TLS#52, for the first article describing how to prepare for and install a poured adobe floor.

By Tom Lander – New Mexico, USA

Now, weeks later after your floor is 100 percent dry, it’s time to seal and fill the floor with Linseed oil. Here in the South West our floors can dry in a matter of a few weeks but in humid climates error on the safe side.

Materials:

Linseed oil. We prefer raw linseed oil, less petroleum additives then the common boiled linseed oil but the boiled works if you are not concerned about petroleum out gassing. Even raw linseed oil has carcinogenic warning labels. Ask for an MSDS sheet. Linseed oil is made from flax seed.

Citrus Solvent (thinner) or mineral spirits, again petroleum out gassing

We are still learning how to estimate coverage and quantity so I’m not sure how much material is needed for your size floor. Maybe buy 2 gallons each for starters; you can buy linseed oil in 5-gallon lots.

Equipment:

4” paintbrushes, natural bristle is always best but pricey

Electric hot plate or gas camp stove

Large pot or kettle

Approved vapor mask

Safety glasses or goggles

Fan for air circulation/expelling fumes if you feel this is necessary

Rags,

Gloves

Prep floor:

Sweep or vacuum any loose debris and dust. You might want to do a light mopping or sponging. Give yourself time for the moisture to dry before applying the oil.

Procedure:

Heat the linseed oil to almost boiling (do not boil). We are just trying to heat the oil to aide in soaking, absorbing in. This must be done outside with caution, flammable. Another option is to pour the oil into a large deep baking pan, cover with a piece of glass and let it sit out in the sun. Leave an air gap. With either method start with a small batch to get the hang of heating and applying.

Transfer the oil into a suitable container. You can paint the material on or if you are quick, you can pour some onto the floor and swoosh it around with the brush. The only risk here is that you will not get an even distribution of material. Try it. Be consistent and watch how the floor is absorbing. If more than one person is applying, then you might get varying results but by the time you are done it shouldn’t matter. Use up your first small amount then decide how much more (a large batch) to heat for your next go at it. For reference keep track of how much material you use for each coat and offer this info to others.

The floor will soak up this first coat and there should not be any pooling of the oil on the surface. Plan your route of attack so you end up working yourself out the door, window or hallway. You should be able to go back to the start and do a second full strength coat right a way. Remember your shoes will be picking up dirt and dust from the outside so take steps to minimize this. There are disposable booties one can buy to cover their shoes.

What we are trying to do is seal the floor but think of it more like filling the floor. Filling all the little air voids between the sand and clay particles with oil.

The floor will dictate the timing and how much material. Watch how the material soaks in. You might be able to continue with more heated, thinned coats the same day, unless you are tired or sick from the fumes and not wearing a vapor mask.

Diluting:

The first two coats can be applied full strength. For the third and fourth coat combine 75% oil with 25% thinner, heat and apply. Watch the absorption, watch for pooling or puddling but also give the material some time to soak in; you just don’t want it to dry on the surface. Have a rag and thinner handy to wipe up any excess otherwise the material dries on the floor and becomes sticky. If this happens then it’s quite a job to use thinner and rags to clean the floor. Apply at least two coats of this first diluted mix.

Next is a 50% to 50% heated mix. Hopefully by now you have learned if pouring and brushing works for you (certainly faster) or just brushing or maybe it’s time now to just brush. Isn’t this fun learning as you go? Like all earthen materials, they tell you when and what to do, what’s the word? Experience.

Remember, oily rags and brushes are flammable so hang out to dry and do not leave a pile of rags unless it’s in the middle of a gravel driveway and you want to have some fun.

www.bioshieldpaint.com

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