• wood trivia
Method for using the right wood in the right place 〜Vol. 1 Water resistance〜

“Using wood around water”

Do you want to use wood for your kitchen countertop, but worried about it rotting…? Then, try wild cherry or chestnut from Hida area. They contain a substance called tannin and is highly resistant to water, insects, and rot. Which is why they’ve even been used in wet areas since the Jomon period.17692365_1386473868070661_1469121343_o ↑This is a wild cherry kitchen countertop made at Hidakuma.

“Wood rot mechanism”

What causes wood rot in the first place? Is it water? The answer is no. Horyuji, the world’s oldest wooden structure, has been exposed to rain for over 1,000 years, but is not rotting. Wood rot is caused by a fungus called “wood decay fungus” that decomposes wood. Wood decay fungi need certain conditions to grow and the most important condition is “high humidity.” Their optimal living environment is a place with a humidity of over 80%. When wood remains wet and is not allowed to dry, fungi become most active. In other words, fungi favor “constantly humid spaces (bathroom, kitchen, sink)” over the “outdoors that are exposed to rain.”

“Trees absorb water”

One of the causes of fungi growth is wood absorbing water. Originally, trees absorb water and nutrition from the ground and circulate them. (I will explain why trees don’t rot later.) Even in the form of planks, they have the same structure and are absorbing and releasing water and moisture, and “breathing” all the time. When trees can’t absorb and release water, in other words when they can’t breathe, wood decay fungi grow and cause wood rot.

“Conditions for preventing wood decay fungi growth”

To prevent wood rot, you must prevent wood decay fungi growth. Fungi thrive when certain conditions meet. So you just need to make sure these conditions are not satisfied.

  • Control the humidity. You can reduce fungi growth by designing the room itself to be well-ventilated.
  • Don’t let wood absorb water. If it does, allow it to dry. Wood absorbs water from cut ends, so it is important to keep cut ends away from direct contact with water. Also, avoid excessive poly coating that interferes with the wood’s breathing.
  • Use fungus-resistant wood. Some wood are resistant to fungi, while others are not. Non-resistant wood will rot easily.
  • Apply water-repellent paint. There are water-repellent urethane paints and glass coatings. Some paints seep into the wood and harden. Although coatings repel water effectively, make sure the coating does not come off.
  • Don’t leave wood wet. Remember to keep it clean.

“Wood decay fungus-resistant wood”

“Rot-resistant wood” contain much substances such as polyphenol, tannin, etc. that wood decay fungi “dislike”. Below are Hida’s broad-leaved trees that fall under this category.

  • Chestnut
  • Wild cherry
  • Zelkova
  • Magnolia

For example, Oak is extremely hard so it suits structure segments that demand durability. But compared to the above wood, it is not antibacterial and not suited to the wet areas. Chestnut and magnolia are soft but highly antibacterial and as a result, rot-resistant. “Hard wood” does not always equate with “durability.”


↑Over counter types (placed over) are recommended for sinks. Under counter types (installed from below) expose the vulnerable cut ends to moisture and promote fungi growth.

IMG_1523 ↑Wild cherry was applied to make the sink fixture. It is given an urethane waterproofing treatment, not oil, and has a rather glossy finish. But using antibacterial wood and waterproofing it doesn’t mean you can splash it with water. No matter how durable the wood is, it will eventually rot. Also, areas near the bark are called “sapwood” or “alburnum,” and they used to channel water and nutrition as trees. These areas absorb much moisture even as planks. They also contain abundant sugar and starch, which are favored by wood decay fungi. These areas are white and easy to tell apart. Sometimes “ears” are used for design purposes, but they are prone to rot and should not be used in the wet areas.
 ↑Alburnum is the white part of wood near the bark. This is where nutrition is carried in trees. Sterilizing substances are condensed in the inner dark parts. The reason trees don’t rot even though they absorb water from the ground is that their cores are filled with these substances. If you understand the conditions and countermeasures for wood rot, it is possible to use wood in wet areas. The most important method for crafting is understanding the characteristics of wood and using the right wood in the right place, not for mere “texture.” I hope this is useful! By the way, wood decay fungi are actually shiitake mushrooms (although they’re just one of many decay fungi). They make things rot, but can also make a yummy dish sometimes. What’s the connection between the umami component known as shiitake extract and broad-leaved trees? Hidakuma is planning to further investigate the relationship between fungi and wood. The more you learn about wood, the more interesting it becomes, doesn’t it? This series will be sharing more wood trivia in the future.

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