Susa （Fibers）

Susa is a fibrous material mixed into earthen walls and shikkui. Much like rebar in concrete, it serves to bind the layers of plaster together, preventing cracks that form as the plaster dries and shrinks. It has long been an indispensable material in shikkui, traditional Japanese plastered walls.

The basic rule is to choose based on “which stage (layer) it will be used for.” As a general guideline, use longer, stronger fibers for the lower layers, and shorter, finer fibers as you get closer to the finishing stage.

• Rough plastering, minor repairs, and leveling → “Hino Hikari” straw fiber (40) with longer fibers (approx. 40 mm)
• Re-coating and intermediate coat → “Hino Hikari” straw fiber (20); for a lime plaster intermediate coat, use Manila straw
• Top coat and finishing → Fine straw. For earthen finishes, use “Asahi” minced straw or Juraku straw; for lime plaster, use Shirayuki

Rice straw contains “tannins” (substances such as tannic acid), and if used untreated, it can cause stains or yellowing on white plaster or light-colored finishes.Straw that has undergone a tannin-removal treatment prevents this, so for white plaster or light-colored finishes, we recommend products marked “Tannin-Removed” such as “Tannin-Removed Straw (Special)” or “Shirayuki.” For base coats, intermediate coats, or earthen wall finishes where color bleeding is less likely, you can use the straw without tannin removal without any issues.

Warasusa is made from rice straw and is widely used for earthen walls, from the rough coat to the finish coat. Manilasusa is made from Manila hemp fibers; because the fibers are strong and the color is whitish, it is well-suited for plaster (especially the intermediate coat).As a general rule of thumb, “use warasusa for earthen walls, and hemp-based materials (Manila sasa) or Shirayuki for plaster walls.” Remembering this makes it easier to choose the right material.

These are the names of the rice (straw) varieties used as raw materials. Even though they are all “warasusa,” the texture of the fibers varies depending on the variety and region of origin; therefore, we have clearly listed the variety names so that you can select the one best suited to your intended use. All are produced in Oita Prefecture. This variety is specifically cultivated by Harada Saken Co., Ltd., located in Oita Prefecture, for use in earthen and shikkui walls.