One spring in the late 1990's, we were invited to Japan to conduct a workshop in rammed earth. At the workshop we met Japan's most renowned and respected plasterer, Akira Kusumi. Among his other work, Kusumi is responsible for the periodic re-plastering of the Imperial Temple. All traditional plaster in Japan is clay-based. We became friends at the workshop, traveled to Kyoto for another visit together, and then I invited Kusumi to Napa to conduct a plaster training for our crew.
When it came time to develop the earth plaster formulas for the Shipwreck experimental station, we of course asked Kusumi to come and help us. Not only did he bring his expertise, but two boxes of Japanese plastering tools as gifts. We had three different soils, a black, brown, and red: a yellow sand, a gray sand, Hawaiian cement, and hydrated lime. Kusimi was looking for the right combination of gritty and sticky. He'd try a certain proportion of soil and sand and test it on his hawk for texture until it had the feel he wanted.
He actually used several different formulas throughout the house. For base coats on the interior walls he'd use copious amounts of long-chopped straw, and low-cement contents. For finish coats we used less straw, chopped finer, and lime rather than cement. Lime gives you more time to work the plaster smooth. Cement plaster is harder and more resistant, but also more difficult to work, especially for amateurs, which we certainly were. For the entry he used traditional Japanese plaster - pure earth and chopped straw with no cement or lime. With no stabilizer, you can come back the following day and steel trowel a final finish, tightening the surface and working out the small shrinkage checking.
Kusumi and Masako were here for a week. We worked pretty much all the time, and finished all the interior partition walls as well as finish coats over the hand-thrown walls in the bathroom and the kitchen. Kusimi's mastery of his craft was remarkable to observe. He could cover a wall in one-tenth the time it took either me or Khyber, and where our work ended up full of trowel marks and cat faces, his was smooth and flat. I have all of the formulas recorded in the formula log. Let me know if you're interested.
Thanks for sharing your earth plaster experience!
ReplyDeleteI am trying to apply earth plaster to our inside walls of our stucco home, and to some rammed earth outdoor garden walls. We are located in the high desert, north of Las Cruces, New Mexico. If you're still willing to share your recipes or have some good reference, I would greatly appreciated it:) Can you provide info/recommendations about the difference for outdoor wall plaster vs indoor plaster. THANKS!!!