Yakisugi (焼杉) is a traditional Japanese method of wood preservation by slightly charring the surface of the wood to increase durability. In the West, it is also called Shou sugi ban (焼杉板).
For hundreds of years Yakisugi was primarily used in Western Japan for exterior siding and fencing on traditional Japanese houses. However, this charring technique was not transmitted to Eastern Japan.
In the Kanto region they were using black paint to achieve the same look finish.
True black color finish is rare in the world and to this day it is still not clear why this technique is only transmitted to Western Japan.
The technique of burning the surface of the wood improves the weather resistance performance, prevents decay, rot, and insect infestation, and makes the wood more resistant to fire than a non-heat-treated cypress plank.
It is often said that this authentic traditional Japanese heat treatment process is a gift from mother nature rather than a scientific construction method technique.
Traditionally, it used to be craft manual burnt on site by carpenters.
In the traditional procedure, three boards of Japanese cedar (Sugi) are bound together with a wet rope to form a triangle pillar shape.
After binding the boards tight, fire is lit on the very bottom with some rounded paper or newspapers. In the past, sawdust was used instead of newspaper.
When the triangular pillar is put up, it takes a minute or two for the fire to proliferate, usually it starts to spread fairly quick due to the chimney or stack-effect from the triangle of boards.
When the surface of the plank is sufficiently burnt, the triangular pillar is open and the fire extinguished by applying water to cool it.
The combustion time is about 5 minutes.
Since the 1970s, mechanization has progressed, and the Yakisugi boards currently in circulation have been charred by high-temperature burners.
Originally all the process was done by hand and nowadays the mechanization process is now generalized.
In Japan, it is generally recognized as for exterior use and is rarely used in interiors.
Processing method of Yakisugi
It was originally used for traditional Japanese architecture (exterior siding and fences), but due to changes in Japanese housing styles and construction methods things changed.
In recent years, not only the exterior but also the interior wood material has attracted attention not only from Japanese architects but also from overseas for residential and commercial projects due to the weather resistance performance and unique design of the Yakisugi.