By Kyle Holzhueter
Editors note: This is a full-length, instructional article. It is the type of in-depth information that you will only find here at TLS.
Kyomigaki, also known as Otsumigaki, is a polished earthen-lime finish often used in entrance ways and stair wells, that is, anywhere a more durable finish is desired. In pre-industrial Japan, due to its energy intensive nature, hydrated lime was a valuable commodity and was used sparingly. Kyomigaki uses roughly the minimum amount of lime needed to polish an earthen plaster, which provides a more durable surface than mizugone or nori-tsuchi, other popular earth based Japanese finishes. The following describes the preparation and application of Kyomigaki. My gratitude to the Kyoto masters for sharing their tradition.
Preparation of Materials:
Haitsuchi Brown Coat
The material ratio is 1 : 1 : 0.4 of clay : fine straw fibers : hydrated lime.
A combination of native Kyoto soils, white clay and Juraku soil 1:1 to 3:1.
All clay is sifted through a 1.5mm sieve.
Fine Straw Fibers:
Mijin fine straw fibers are sifted through a 1mm screen. The powder that falls through the sieve is saved for Mizugone, a different finish, and not used for Kyomigaki’s Haitsuchi brown coat. If the straw fibers are rather large, they should be separated again with a 5mm sieve. The fibers that do not pass through the 5mm sieve are too large for Haitsuchi and should be saved for a different purpose. In other words, the fibers should be between 1-5mm in length.
Dry mix the Juraku soil and white soil and then mix with water.
The dry clay is mixed with water, and then the straw fibers are added. To ensure full saturation of the clay and straw fibers, this mix should sit hydrated for one week.
Clay mixed with fine straw fibers and allowed to ferment for one week. Due to the fine nature of the clay and fibers, this mixing trough of materials is valued at over $1000USD.
To reduce the cost, Hidashi straw fibers can be used in place of the fine mijin straw fibers. However, after the finish has completely dried, the outline of the Hidashi straw fibers in the sub-layer may be visible.[restrict userlevel=”subscriber”]
Sift hydrated lime through a 1mm sieve.
On the day of applying the finish plaster, mix hydrated lime with some water, then add the mix to the fine earth-straw fiber mix.
Hikitushi (Noro) Finish Coat
The top coat (noro) consists of fine clay and Washi paper fibers, and is mixed with hydrated lime immediately before use.
Completely dry the colored clay before soaking. Preferably the clay is crushed after thorough drying. If placed in water while the clay still contains moisture, the clumps of clay may be difficult to break apart.
Soak colored clay and paper fibers in water for 1-2 weeks.
Mix clay with a hand mixer.
Sift clay through a 100-150 mesh.
Wash sieve regularly.
After soaking, tear apart Washi paper fibers.
Remove paper fibers from the soaking bucket and pound the saturated fibers on a flat stone with split bamboo. The pounding softens the fibers and breaks them apart.
After pounding, put a handful of fibers in a bucket of water and stir vigorously to unwind the fibers. Remove any unbroken paper fibers, which appear as white clumps in the water.
Strain the paper fibers through a sieve and collect the prepared fibers into a separate bucket.
Prepared paper fibers
Mix the strained colored clay and paper fibers. Approximately one tennis ball/baseball size of straw fibers per 4-5 liters of sifted and hydrated colored clay.
After mixing the clay and paper fibers, stick your hand into the mix and pull it out. You should see the paper fibers like a web between your fingers.
Allow the color clay and paper fiber mix to sit for at least 24 hours and up to one week.
On the day of application, remove the standing water over the settled clay and paper fibers and mix with a hand mixer.
Before mixing with sifted hydrated lime, check to ensure that washi paper fibers have broken apart.
Sift hydrated lime through a 100-150 mesh.
On the day of applying the finish plaster add the sifted hydrated lime to the clay and paper fiber mix at a ratio of approximately 1 part hydrated lime to 3 parts clay and paper fibers.
A number of trowels are used throughout application and polishing. The most important trowels are (1), either (3) or (4), and (5), shown below.
1. Jigane application trowel
Whereas a steel trowel will tend to slide over plaster, iron Jigane trowels will naturally push and pull material, evening the plaster.
Well worn Jigane trowel
Jigane trowels available at Japanese Plastering
2. Fusekomu Jigane Trowel: Significantly worn, narrow Jigane Trowel
The purpose of the Fusekomu Jigane trowel, as will be explained below, is to drive the fibers back into the wall after rewetting. To ensure that the trowel doesn’t catch and damage the wall, a worn, narrow Jigane trowel is used. If this trowel is unavailable, a polished Jigane trowel can be used for the same purpose.
3. Polished Jigane trowel for evening and compression.
After application, the polished Jigane trowel is used to even the surface and for deep compression. Whereas a steel trowel will tend to only compress or polish the surface, the Jigane trowel compresses the entire thickness of the plaster, resulting in a deeper compression and fuller polish. This trowel must not be used for any other purpose, and especially not with plasters containing sand aggregates, which would scratch the trowel. The edges of the trowel must be polished with 1000 grit sand paper or higher. Any micro scratches in the trowel might scratch the surface of the finish.
4. Konashi Trowel
Almost any trowel can be used as a Konashi trowel for compression as long as the plate of the trowel is meticulously polished. Yamanishi-san’s Blue Paper no. 1 Honyaki trowel is an excellent choice.
5. Honyaki polishing trowel
Traditional Kyoto Polishing trowel
Yamanishi-san Ultimate Finishing Trowel
In addition to being meticulously polished, the polishing trowel consists of the hardest honyaki steel, the same steels used in Japanese sword making.
Apply an even Haitsuchi with a Jigane application trowel and compress with a polished Jigane trowel.
After the mix has stiffened, and will draw moisture, apply the Hikitsuchi/noro.
Apply and compress with a Jigane application trowel. As the mix stiffens, compress with a polished Jigane trowel. When there is too much friction for the polished Jigane trowel, compress with a polished Konashi trowel.
When the surface can no longer be polished due to friction, re-wet the surface with a cloth. Quickly drive the loose paper fibers back into plaster with a worn, narrow Jigane trowel. The narrow, worn nature of the trowels allows for quick, easy movement.
Compress with the polished Jigane trowel, and then with the polished Konashi trowel. If you have a uniform texture and color, you may then move on to polishing with a honyaki polishing trowel when the konashi trowel can no longer be used due to friction. If there are some variations in color or texture, re-wet the plaster again and repeat the previous steps.
Slowly polish the surface with a polished Honyaki polishing trowel, covering the wall 2-5 times. Be careful not to scratch the surface. When there is too much friction, move on to the next harder trowel. When there is too much friction for the polishing trowel, clean and organize the worksite, return home and have a beer.
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