Charred or burnt wood (yaki sugi-ita, yakisugi, shou sugi ban) has evolved from a Japanese technique of preserving and enhancing the look of wood mainly used for the external building envelope i.e cladding. This is done with the use of fire, burning to create a heat treated surface and carbonised layer around the timbers exposed faces.
The History and Process
The processes of burning, charring, blackening of timber have been predominately used on products for external applications mainly external cladding/siding. We now see timber products that have been burnt being used for internal applications such as flooring, decking, interior cladding. Yaki sugi-ita, yakisugi, shou sugi ban timber is now also being supplied in common machined cladding patterns as opposed to the traditional square edge profiles.
The process as illustrated in the video had been prevalent in Japan and used on Japanese Cedar (Cryptomeria japonica– known in Japan as Sugi). Hence you find many terms or brand names used on the market to describe burnt or charred wood have terms based around the Japanese language or traditions of wood, fire, burning. Some of these common names or terms that occassionaly tend to be used interchangeably include yaki sugi-ita, yakisugi, shou sugi ban, suyaki, gendai, hiragana,yakeru, kaho, pika-pika etc.
Yakisugi or shou sugi ban has been a long-standing process dating back to more 100 years in Japan, that has until recently become a choice with many Architects in Europe and North America. The interest in charred wood has come about due to its visual impact and its ability to keep its look longer without the need for maintenance compared to painted or lacquered wood products.
Charred wood should be considered, specified or used for its visual or aesthetic properties. The only exceptions for declaring better or enhanced properties to the natural wood should be in instances where test data from a reputable Notified laboratory has been provided e.g showing improved fire, decay, properties these results will allow you to support any claims.
Most of the burnt or charred wood products have no test data to prove that the timbers natural performance has been increased or improved by burning or charring/ scorching.
Charring or burning of wood for use in exterior applications above ground e.g cladding and decking tends to be done with naturally durable i.e durability class 3 or better softwood species or products. Examples of timbers or products that fall into this durability class 3 and better that are charred include Douglas fir, Japanese cedar (sugi), Western Red Cedar, Thermowoods, Kebony, Accoya, Siberian Larch. The process tends to be undertaken on softwoods as they are easier to charr /burn in comparison to most hardwoods because of factors such as that the softwoods have an open cell structure.
Most of the charring/ burning processes in the UK tend to be manual slow, laborious processes, as most suppliers use manual blow torch burners an example of a DIY project see videos. The process tends to be carried out offsite in factories etc as opposed to onsite/ construction sites.Factors such as limited space and stricter health and safety requirements on construction sites make it not suitable to be done onsite.
The use of blow touches is a more recent technique to the original Japanese technique were they used open fires, with timber was built up into a triangle form resembling a chimney or column for burning see. video
A number of techniques or finishes are used such to give a different aesthetic looks to charred, burnt wood e.g yaki sugi-ita, yakisugi, shou sugi ban these include e.g. burning and wire brushing to provide a textured look, burning and adding a black finish, giving a gloss or satin matt lustre etc.
The heavy burnt – Heavy charred wood tends to maintain its look longer compared to lightly charred / lightly burnt finishes.
Below are examples of burnt or charred wood.
Variation / concerns of Charred burnt Shou Sugi Ban
Due to the substantial potential variations of product finishes between suppliers, including within board and between timber board variations, it is essential to request samples before proceeding with the specification or purchase without a sample or control sample.
A number of points are important to discuss during the purchase or specification process of Charred, burnt wood e.g yaki sugi-ita, yakisugi, shou sugi ban or other burnt timber these include the following:-
- Risk of wash off or runoff off of black soot from the charred wood in situ or onsite
- Risk of contamination from direct contact
- Species that can be supplied
- Some of the Installation, purchasing guidelines etc.
- Profiles that can be supplied
- How will the wood weather, will it be able to maintain the provided look? ( most likely answers will be we cannot guarantee or warranty it)
- Any claims of increased performance should be backed up with test evidence from a recognised laboratory, g. enhanced fire performance, enhanced durability.
- Check ordering and delivery lead times