Close-up of a ricecrete wall I built with Kyle Holzheuter in Japan. We used split bamboo lath to contain the ricecrete and as a substrate for earthen plaster. You can see that not very much lime binder is needed.
In rice-growing regions including California’s Central Valley (where I live) as well as parts of the Southeastern US and many areas in Asia and Africa, rice hulls are an abundant resource. The seed coats of the rice grain--removed during milling--are extremely high in silica, which makes them rot-resistant, mold-resistant, fire-resistant, and resistant to settling. As a loose-fill insulation in walls and roof cavities, they have a very high insulation value for a natural material - approximately R-4 per inch of thickness.
In rice-growing regions including California’s Central Valley (where I live) as well as parts of the Southeastern US and many areas in Asia and Africa, rice hulls are an abundant resource. The seed coats of the rice grain--removed during milling--are extremely high in silica, which makes them rot-resistant, mold-resistant, fire-resistant, and resistant to settling. As a loose-fill insulation in walls and roof cavities, they have a very high insulation value for a natural material - approximately R-4 per inch of thickness.
To address both of these concerns, my colleague Kyle Holzheuter in Japan started experimenting with mixing rice hulls with clay slip or lime as a binder and stabilizer. I have used a mixture of rice hulls and lime (dubbed “ricecrete”) on several projects in California, both in walls and ceilings. Ricecrete is very easy to mix using either a mortar mixer or a regular cement mixer, and since it pours easily and requires no tamping, it requires less labor than either straw-clay or slip-and-chip. Although the use of lime increases both the cost and the environmental impact of the material when compared with clay, it adds to the material’s mold- and rot-resistance. Ricecrete is one of the only natural infill materials that I feel comfortable installing during cold or damp weather, or in a wall cavity that is already sheathed on the outside. (Straw-clay and slip-and-chip should both be installed only during warm, dry weather and in situations where moisture can evaporate to both sides of the wall.) I’m excited to work with this material more, and I’m happy to share my recipes and experiences to date.
Along with my friend Matt Anderson of Earth Lodge Studio, I made this short video about ricecrete.
Mixing ricecrete in a pan-style mortar mixer in Japan.
Ricecrete being installed using slipforms, in a wall cavity that is already sheathed with plywood on the outside. I would not recommend this with straw-clay or slip-and-chip!
