﻿Wood is a natural, renewable and sustainable building material with a smaller carbon footprint
than steel or concrete. Maximizing wood use in both residential and commercial construction
could remove an estimated 21 million tons of CO2 from the atmosphere annually – equal
to taking 4.4 million cars off the road. Softwoods like pine take less time to grow than
hardwoods like oak, so they are a more sustainable option. However, untreated softwood is susceptible
to rot and mold, so it is typically not used outdoors. Well, that’s about to change. In
this video, we’re going to understand how ancient Japanese techniques modify the components of wood
to make them stronger and resistant to decay. 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 is an ancient Japanese architectural technique that was used to preserve Japanese
cedar or Sugi wood. It was invented in the 1700s, when the durability of homes in remote areas
became a major concern. Three wood planks were tied together lengthwise with string to form
a triangular tunnel. Tinder was stuffed into the center of the tunnel and lit on fire. When flames
poured out of the top, and all interior surfaces were scorched, the flame was put out with water.
This process removes both free and bound water inside the wood. The flames and high
temperatures also decompose the cellulose, hemicellulose and lignin in the wood.
This process of slightly charring the surface of the wood without burning the whole piece is called
carbonization. It neutralizes the cellulose or carbohydrates in the wood which is a source of
food. This makes it undesirable to termites, fungus, bacteria and pests. It is water-proof,
fire-retardant and resistant to rot. It can last over 100 years with no intervention.
Unfortunately this method was forgotten when cheaper wood alternatives flooded
the international market. In the 1990s, the VTT Technical Research Center of Finland,
developed a new method of preserving wood, based on the Yakisugi method. They called it “Thermally
modified wood” or ThermoWood. It is a 3 stage kiln process that uses 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.
The sap and pitch is also cooked out. 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, which is the breaking up of the hydroxyl groups in the hemicellulose
of the wood. The planks start to darken as the wood cell components degrade.
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.
Average moisture after this phase is 4-5%. After the wood planks are removed from the kiln,
they are milled down to the consistent sizes with tongue and groove joints.
Arbor Wood, a Minnesota based company sent me these samples of thermally modified wood
for an unpaid, unbiased review. This product has plenty of advantages.
It is one of the most natural ways to extend the life of wood products.
It is free of chemicals, so its more sustainable than traditionally treated lumber
The wood is gorgeous. It has a consistent dark appearance throughout, not just on the surface.
It looks a little like caramelized sugar. Because the hydroxyl groups in the cells are
decreased, it is water repellent. It is also fire resistant.
It is dimensionally stable. It doesn’t expand or contract much, it doesn’t warp or cup
Because the natural acids and sugars are affected in the kiln, the wood is not a
food source and is resistant to rot and mold. It is lightweight because of its low moisture
content. In fact, it is significantly lighter than the greenish, pressure-treated outdoor lumber.
It is maintenance free. It has a long lifespan of 20-30 years.
We can use cheap, rapidly renewable pine wood to make long-lasting, outdoor rated products.
We can use domestic wood instead of hardwoods sourced from rainforests.
We can even use beetle-infested pine that might have been thrown away.
You can find a wide variety of finishes from traditional ash,
to burned and brushed to a white washed finish. Thermally modified wood can be used for outdoor
decks, siding, interior flooring, millwork windows, doors, bathroom interiors, saunas
and outdoor furniture. It is also used to make bridges
and necks for guitars since it doesn’t warp and always keeps the instrument in tune.
Now, the disadvantages of thermowood. Thermal degradation & a lower
moisture content makes it brittle. It is more expensive than untreated softwood,
but around the same price as hardwoods, at least before the blip in lumber prices.
It is not structurally sound and cannot come in contact with the ground.
Oils, stains, and water based finishes don’t work on thermowood because it’s hydrophobic.
Some adhesives that rely on soaking into wood fibers to bond, may also not work.
Because the wood goes through a lot of stress in the kiln, you must use premium
grade planks without large knots. The wood shrinks about 5-10%, most of
the loss of wood is from milling and machining The wood is not UV stable. The color changes
to a soft gray over time. If you want to maintain the brown tone,
you have to use pigmented top coats. Arbor Wood has a product that uses the
Yakisugi burning technique on top of a piece of ThermoWood. The result is a beautiful charred
black top surface with visible grain. It is much more aesthetically pleasing than a black stain.
The idea of using sustainably harvested softwood for outdoor applications is very exciting.
The energy consumed while heating the wood in kilns is a little bit of a concern, but you have
to take its long lifespan into consideration. And it doesn’t use any harmful chemicals. Arbor
Wood is building a facility in Minnesota that will capture all the heat emitted from the kilns
and use it to heat their buildings, which will create a closed loop. Let me know what you think
about this product in the comments below. I’ll link my Patreon page in the description. If you
can support me, I’d really appreciate it. A big thank you to everyone already supporting me. Don’t
forget to hit the like button and subscribe to my channel. Thanks for watching. See ya.