What is yakisugi
The story of burning timber cladding is centuries old.
Traditionally Yakisugi (Shou Sugi Ban ) is a fence, ceiling or weatherboard cladding made exclusively from Japanese Cypress(Japanese Cedar). This process started 600 years ago to improve the life of Japanese homes. Like all building materials over time we discover new way and new better materials to produce a product. As such modern shou sugi ban is made from a wider range of timbers today for many different characteristics. Fire conditioning these timbers under immense heat serves as a preservative and has a stabilising effect on the wood.
How is Shou Sugi Ban made?
Historically, Yakisugi (Shou Sugi Ban ) has been made by the Japanese contractor on each jobsite. The yakisugi contractor would create a 3 board chimney and light a fire inside the chimney. Each 3 board chimney would need to be rotated and for a second fire in the opposite end to ensure even charring along the length of he timber. As you can imagine this was a long and slow process.
Only in the last several decades has Yakisugi (Shou Sugi Ban ) manufacturing transitioned to timber mills and professional shou sugi ban manufacturers like us. This is due to the demands of Architects and the need for highly consistent production of the construction market. In Japan a holistic and narrow manufacturing protocol has been developed over hundreds of years to ensure dimensional stability and maximum longevity, which we have studied replicated in New Zealand.
The fire conditioning is intense, and the wood is quenched at the perfect time. Then it is dried again so the timber is ready for the customer in the charred Sendai finish. Or the charred timber is then brushed to remove charred layer to reveal the textural beauty to achieve the desired appearance. Standard traditional products include Suyaki (original charred), Gendai (brushed once), and Pika-Pika (brushed twice).
How does Charring timber work?
The Shou sugi ban heat treatment improves cladding longevity by preventing decay and insect infestation, makes the boards more dimensionally stable, and improves fire retardancy.
Wood is predominately made of structural lignin, with hemi-cellulose carbohydrates which are food for fungi and insects. Fire conditioning of Yakisugi (Shou Sugi Ban ) burns off the cellulose, removing the primary food type and minimizing rot and infestation. The fire conditioning treatment also case hardens the timber, and in combination with air drying, improves dimensional stability in severe weather exposure. The charred layer increases the temperature threshold needed for combustion, significantly reducing flame spread. The charred layer is also a natural hydrophobic protection against weathering.
Does the wood truly become a no-maintenance timber product?
In Japan the answer is yes. In New Zealand No. Yakisugi (Shou Sugi Ban ) is a very low maintenance timber cladding finish which only needs to be re-oiled at least every 5 years to slow down the weathering process.
All Yakisugi (Shou Sugi Ban ) surfaces start off with the boards being deeply heat treated to the charred finish of Suyaki.
From there we brush the boards to next to achieve the Gendai finish. The pike Pika-Pika finish is lightly burnt and brushed again. Suyaki’s thick soot layer will keep the same colour for up to 80 years depending on burn quality and site conditions. However, the Gendai and Pika-Pika brushed surfaces will weather over time and we advise a 3-5 year oiling cycle for a smart appearance.
With Yakisugi (shou sugi ban) we must differentiate between wood and colour longevity. While heat treatment preserves the wood, a re-oiling schedule is necessary to maintain colour. We recommend you live with your Yakisugi (shou Sugi Ban) for several years before considering re-oiling, given the chance you will enjoy how the product develops a rich patina with time — not to mention avoiding the unnecessary maintenance costs.
Many timbers are excellent for charring, some are not suitable like Western Red Cedar as its char falls off very quickly. Siberian Larch, Californian Redwood, Lawson Cpyress, Thermally modified pine (Abodo, ThermoWood Accoya) and of course Japanese Cedar are all excellent timber for the process.
The ideal characteristics we look for are straight-grained, fast-drying, tannin-rich, stable and strong timber— very much all desirable characteristics for timber cladding. Most importantly a thick, dense latewood growth ring, which burns to a more substantial, longer-lasting char layer. Many timbers in teh cypress family have chemical properties that respond well to fire, and it becomes incredibly dimensionally stable when milled, dried, fire conditioned in the traditional Japanese way.
In Japan the largest forestry company who produces Yakisugi is Nakamoto forestry, and they will only use Japanese Cedar.
Our experience has shown that hardwoods promise greater longevity, but do not live up to the environmental standards of Yakisugi (shou sugi ban) or fire well with the traditional process.
If you are looking at these alternatives, we stress that you must take the long-term perspective. We trust our cladding to look great without any maintenance for its lifetime in New Zealand. Chemically treated wood, hardwoods, or faux finishes will always weather inconsistently and do not have the in-service history to prove their durability or performance over time.