The Complete Guide to Yakisugi Charred Wood Siding

January 26, 2022

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Yakisugi, an ancient Japanese architectural technique, was developed in the 1700s to preserve Japanese cedar or Sugi wood. In this article, we explore this eco-friendlly and durable solution for construction projects.

Introduction

Wood has long been celebrated as a natural, renewable, and sustainable building material with a smaller carbon footprint than steel or concrete. By maximizing wood use in construction, we could potentially remove 21 million tons of CO2 from the atmosphere each year, equivalent to taking 4.4 million cars off the road.

When it comes to sustainability, softwoods like pine outshine hardwoods like oak due to their faster growth rate. However, untreated softwood is susceptible to rot and mold, limiting its outdoor usage. But now, we’re about to explore how ancient Japanese techniques have revolutionized wood preservation, making it stronger and highly resistant to decay.

Components of wood fiber

Wood fibers are composed of several layers called cell walls. The 3 main components of a wood cell wall are similar to those of CMU block wall

Cellulose is like a concrete block. It is an important structural component.
Hemicellulose is like the mortar, it is a supportive matrix that strengthens the cell wall
Lignin is like rebar. It is a mechanical support that provides resistance to stresses

Moisture is responsible for the expansion and contraction of wood. It exists in 2 forms: free and bound water.

Free water and vapor are found in cell cavities, voids or lumens in wood. It contains dissolved minerals, nutrients and sugars. It enters and exits the wood depending on temperature, humidity and environment.
Bound water molecules are held within the cell walls. They combine with hydroxyl groups in the cellulose to cause wood rot, decay and fungus.

Yakisugi / Shou Sugi Ban

Yakisugi, an ancient Japanese architectural technique, was developed in the 1700s to preserve Japanese cedar or Sugi wood. The process involved tying three wood planks together to form a triangular tunnel, stuffing tinder in the center, and setting it on fire. When flames poured out and the interior was scorched, the fire was extinguished.

This carbonization process removed both free and bound water and decomposed the cellulose, hemicellulose, and lignin in the wood. As a result, the wood became water-proof, fire-retardant, and resistant to rot, making it undesirable to pests and fungus. It could last over 100 years without intervention.

Thermally Modified Wood

Although the technique was forgotten due to cheaper alternatives flooding the market, the VTT Technical Research Center of Finland reintroduced it in the 1990s as “Thermally Modified Wood” or ThermoWood. This method employs a 3-stage kiln process using only heat and steam.

In phase 1, carefully selected dried wood with a moisture content of 12% is placed in a kiln. It is heated to 100-150 C for 48 hours. The moisture content of the wood is reduced to nearly zero.
In phase 2, the temperature in the kiln is rapidly increased to 180-240C and plateaus for 4 hours. This high heat and lack of oxygen causes hydrolysis.
In phase 3, the temperature inside the kiln is decreased and steam is pumped in. This helps cool the wood and increase the moisture content of the planks to improve stability.

Advantages of Arbor Wood

Arbor Wood, a Minnesota-based company, offers thermally modified wood products that come with numerous advantages:

Natural preservation without the use of chemicals, making it more sustainable than traditionally treated lumber.
Gorgeous, consistent dark appearance throughout the wood, resembling caramelized sugar.
Water-repellent and fire-resistant properties.
Dimensional stability, preventing warping and cupping.
Resistance to rot and mold due to affected natural acids and sugars in the kiln.
Lightweight with low moisture content, significantly lighter than greenish, pressure-treated outdoor lumber.
Maintenance-free and a long lifespan of 20-30 years.

This innovative wood opens up possibilities for using cheap, rapidly renewable pine for long-lasting outdoor products and reduces reliance on rainforest-sourced hardwoods. It can even be made from beetle-infested pine that would have otherwise been discarded.

Conclusion

Arbor Wood’s use of the Yakisugi burning technique on top of ThermoWood creates a visually stunning charred black top surface with visible grain, far more appealing than traditional black stain. Moreover, Arbor Wood’s commitment to sustainability includes a facility in Minnesota that captures all heat emitted from the kilns, creating a closed-loop system.

In conclusion, Yakisugi burnt wood siding and Thermally Modified Wood offer an eco-friendly and durable solution for construction projects. With their long lifespan, reduced carbon footprint, and chemical-free preservation, these products pave the way for a greener and more sustainable future. Share your thoughts on this innovative product in the comments below!”