Interesting Woodworking

Japanese Technique of Preserving Wood – Shou Sugi Ban

Surface charred wood (also known as Shou Sugi Ban) has become an international sensation. However all charred timber is not created equal.

Surface charred wood – an ancient Japanese technique known as Shou Sugi Ban has become an international sensation – with recent articles in the New York Times taking things to a fever pitch.

However all charred timber is not created equal. In the rush to char wood, it is safe to assume there has been some short cuts taken and misunderstandings about charred timber and its lifespan.

Firstly, the choice of timber is critical. Open celled timbers work best, as during the charring process the outermost cellulose burns off, which leaves blackened lignin behind. Depending on the level of char, this can create a very charred alligator type skin on the wood.

The Japanese process has typically used Sugi (cryptomeria japonica) a soft, naturally durable timber native to Japan. For this reason softer. stable naturally durable timbers work best. It is critical than a minimum of 2-3mm of char is created in order to create a “wear layer” when the wood is exposed to weather. Many hardwoods do not achieve the depth of char required to provide long lasting durability, beware of charred hardwood.

Secondly, char depth is critical. A heavy char will last longer than a light char, due the way wood weathers when exposed to weathering. When exposed to rain and UV, wood slowly erodes, and it is this sacrificial char layer that erodes, maintaining the black char colour, along with it’s preservative benefits. Abodo uses proprietary oils to create a harder char layer, which in turn reduces flaking of the coating, and improves durability of the char layer.

Brushing the charred wood often creates a beautiful appearance which can be finished with a natural oil. This finish is more suited to interiors, and will quickly weather once exposed in an exterior environment.

So, how long will a properly charred timber last, when exposed to the full ravages of weather? It is most certain that it outlast all black semi transparent oils and stains. But the truth is no-one really knows.

Abodo testing has indicated that a 2mm char will last for 5 years at minimum, in a fully exposed application. Regular coating of Char Oil will help maintain the surface char, and colour integrity ongoing.

Due to the variability of factors associated in the process there is certain to be mixed results. However the process certainly has a long life span, with Japanese examples of Shou Sugi Ban lasting for well over 50 years

Source

Northmen’s video of this technique:

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