Shou sugi ban (yakisugi)

Overview

Shou sugi ban (also yakisugi, Japanese for burnt cedar board) is a traditional Japanese method of preserving wood. Wikipedia describes partially charring the surface of the wood, without burning through the piece, so the surface is carbonized. The article says carbonization makes the surface water-resistant, reduces hygroscopy and increases durability, and that it protects against insects, fungi and mould and adds fire resistance. In the West it is also called burnt timber cladding. It is a technique rather than a product, used on cedar, usually for cladding and, increasingly, for interior accents and furniture.

Pros

• Distinctive black or charcoal appearance, with no pigment or dye involved.
• Wikipedia lists protection against insects, fungi, mould and fire as traditional claims.
• Wikipedia notes it shares features with modern thermal wood modification.
• Traditional, long-standing practice in Japan (Wikipedia calls it a traditional method of wood preservation).

Cons

• Wikipedia reports that some studies show surface charring alone does not improve durability or resistance to fire or water. Treat the preservative claims with caution, and do not rely on charring as a fire retardant.
• Messy and labour-intensive; charred surfaces are likely to shed soot unless cleaned and sealed (general experience, not a figure from the sources opened here).
• A real flame is used; there is a fire risk in the shop and on site.
• Hard to repair; a damaged spot is difficult to match.
• Only the surface is changed, so any cut edge or end made afterwards is bare wood.

Suitability

Traditional on Sugi (Japanese cedar), and used on Western red cedar and similar softwoods. Suitable for cladding, fences, planters and accent pieces. For furniture and tabletops, charred surfaces rub off and need sealing; consider that the look is more important than the protection. Not for food-contact surfaces.

Coats and application

Wikipedia gives only the principle: partially char the surface without combusting the entire piece. No schedule, flame type or depth is given in the source opened for this entry, so use a reputable woodworking or forestry reference for the method, and test on offcuts first. Whether and how to seal afterwards is a separate decision: soot can rub off, and a sealer such as Tung oil or Boiled and raw linseed oil is a common choice, but follow that product's instructions.

Compatibility

Any later finish goes over the charred surface, so test adhesion and rub-off on a sample board. Match the finish to the exposure (Outdoor finishing). Never char over an existing finish: burning finishes can release hazardous fumes.

Care and repair

Care depends on what, if anything, you applied afterwards. Damaged char is difficult to repair invisibly; local re-charring or touching up with the same sealer is the usual approach, and a blended repair is hard.

Safety and environment

Open flame: work outdoors or in a space cleared of dust and flammables, with water and an extinguisher at hand; never leave smouldering boards unattended. Burning wood produces smoke and fine soot; wear a respirator and eye protection. Oils used afterwards bring the usual oily-rag hazard (Oily rag safety). Check local rules before doing hot work.

Related

• Tung oil: common sealing oil.
• Boiled and raw linseed oil: traditional oil.
• Outdoor finishing: exterior systems.
• Linseed oil paint: traditional exterior coating.
• Wood graining and faux finishes: other decorative effects.