DIY: What’s the Best Way to Brush Your Own Shou Sugi Ban?

Setting the Stage

Our two main mills in Hiroshima and Tokushima Japan are the largest yakisugi “shou sugi ban” millwork operation in the world, with a proprietary high-volume semi-automated millwork and heat treatment manufacturing setup. This is very different from the local jobsite burning and brushing that has historically been how shou sugi ban was made. 

In Japan shou sugi ban is a common, traditional building material, and our employees there have not made it themselves by hand out of DIY curiosity. But for us distributing the material overseas the cultural and historical stories are really engaging, and so we decided to make it ourselves for fun. We were curious to see how easy or difficult it actually is to make by hand, what techniques work best, and how the hand-made product differs from the machine-made product.

Getting Started: Burning Shou Sugi Ban

So a few weeks ago we set out to a farm near Mt. Hood with 50 unburned sugi boards to try creating our own shou sugi ban using the traditional Japanese flue method. While it took a few tries to get the process down, we ended up with around 40 usable boards of the unbrushed product we call Suyaki. 

All of our yakisugi starts off as Suyaki, and after heat treatment the soot layer can be brushed down to what we call Gendai and Pika-Pika products. The burned and dried planks have traditionally been used as-is for siding, or brushed down to achieve a smoother, more refined surface appearance. So the next step in our DIY shou sugi ban-making process to get to know our product better was to brush down the soot layer of some Suyaki boards and make them into our Gendai and Pika-Pika products.

The Basics of Brushing Shou Sugi Ban

The brushing step is traditionally called “arai” (洗い), meaning “washing” the planks. The heavy soot layer is brushed off of the boards by hand and water, turning the scaly, black surface of the shou sugi ban into a smooth, brown wood surface. 

The DIY Shou Sugi Ban Brushing Process

Arai brushing has been done in Japan for hundreds of years, far before modern automation of the process. We knew the basics of doing it yourself: 

1. Use a brush to scrub the soot off of the surface of the boards
2. Use water to mitigate dust and wash the soot off. 

There are different methods and tools we’ve seen used, so we wanted to try a few of them to see which worked best for specific results. We also wanted to restrict our tools to a standard jobsite kit available to anyone.

One note is that we did these tests at our warehouse in Portland and could not do arai outside with a hose such as on a jobsite. In a future post we will show how to do it on the jobsite.

We put together a variety of brushes with different bristle lengths, rigidity, materials, and sizes, based on what we’ve seen carpenters in Japan use. We tried short-handled brushes on saw horses with and without water, also long-handled brushes on the ground.

We brushed with and across the grain, and with and without water to see what gave the best end results. After hours of experimentation and a flood of black sludge covering our floor, we came to a few conclusions.

For any DIYers out there who want to give this a shot, here’s what we learned:

1. Choose your shou sugi ban brush
2. Grab a partner
3. Brush across the grain, or along the grain
4. Have your partner pour water on the board as you brush

The Five Different Shou Sugi Ban Brushing Methods Tested

1. Hand Brush Across the Grain: This is definitely done most efficiently as a two-person operation and the planks laid on the ground. One person brushes vigorously while someone else pours water along the board in front of the brush. The more water the better since this reduces viscosity of the slurry and makes the brushing easier. It sort of feels like curling in a weird way. Then any touch up can be done by one person with a short-handled brush on saw horses.

2.  Long Stiff Bristles Along the Grain: A large nylon or natural brush with long, stiff bristles, and on a long, rigid pole will give you the best results with the least effort for removing the majority of the soot. Other brushes we tried were either not stiff enough to actually knock the soot off, or too small to be efficient. A short-handled brush with the same long, rigid bristles can be used in a secondary process to touch up the margins.

3. Twice Brushed Shou Sugi Ban: A multi-step process yielded far better end results than any single brushing process. It worked best to make one pass on the ground with the grain to remove the bulk of the soot, a second pass across the grain (as mentioned by Bill in the video below) to knock down the latewood growth ring soot, then a final touchup with a margin brush and lots of water to even out appearance and wash off all the loose soot residue. We also noted that the sugi species we use has a very hard latewood growth ring that was very difficult to brush off. This makes the soot layer last longer in exterior exposure and is one of the main reasons we use the sugi species for yakisugi “shou sugi ban.”

4. More Water: Use water at every brushing step, and really drench the boards. Without water the soot dust is simply unmanageable. The water makes things look messy, but slurry splashing around the immediate area is much better than a hovering dust cloud. We learned that water acts as a lubricant so that less effort is required to do the work, also that the slurry washes the soot material off the boards very efficiently. Cleanup with a shop vac afterwards was a breeze for us but it would be easier on a jobsite where the water could be allowed simply to run into the ground.

5. Manually Brushing: This is a lot of work. Manually brushing the boards down is a maximum-effort process, best tag-teamed by a group. Just brushing one board down is physically challenging, similar duration and effort to running a 400-yard dash. To do this right and at volume would be a challenging undertaking.

Check out our video from the day to see exactly how things went for us! 

The Results

So there you have it, a beginner’s guide to DIY brushing shou sugi ban to create a beautiful, smooth Gendai-like surface. As with the burning process, we learned just how much effort and technical challenge it is to create a large volume of high-quality boards with a consistent aesthetic. It was very rewarding and we learned a lot about our product.