Why Steaming Wood Makes It Bendy

Wood is perhaps the oldest building material out there. In fact, the oldest standing wooden building is in Japan and dates back to 607 AD. With centuries to experiment with techniques and methods of building with wood, it’s of little surprise that humans have discovered unique ways to manipulate and build with it. One of the most interesting ways of building and constructing with wood is a process called “steam bending”. 

What Is Steam Bending?

Steam bending is a woodworking technique that involves steaming pieces of wood to make them bendy. This process has been used for centuries to construct boats, athletic sticks such as lacrosse or hockey sticks, instruments, furniture, weapons, tools and more. 

The History of Steam Bending

Steam bending is first attributed to Michael Thonet in the 1840s. He used the technique to construct a chair. The chair is now known as the Bentwood Chair or Chair No. 14. Since then, steam bending has become more popular and mainstream and is used in a variety of ways, as stated above.

That being said, the process of using heat to bend and shape wood is much older. Historians have even associated heating and steaming wood over a fire that was used as far back as the Vikings to build their ships.

Another version of steaming wood involves soaking wood pieces in hot water to make them bendy. 

But Why Does Wood Bend When Steamed or Heated?

This process is truly a scientific wonder and is only possible because wood is natural plant material. More specifically, the lignin in wood.

Lignin is an organic polymer found in wood and plants. Polymer is a term that refers to a material with a molecular structure composed of large similar particles. Nylon, epoxy and wool are three examples of polymers. 

There are both synthetic and organic or natural polymers. Lignin is one type of natural polymer. 

Lignin exists naturally in plants and is a key structural component that helps to support the shape and structure of cells. Basically, it’s the scaffolding or framework for a plant. It is strong and doesn’t rot easily. This may be why it’s incredibly important in trees for the formation of bark and the actual wood. 

When bending a regular twig or piece of wood, it is lignin that allows it to spring back to shape or - when put under immense pressure - it snaps. When heated, this structural compound in wood relaxes and becomes soft and flexible. It eliminates that “spring back” that can happen. When the wood cools it regains its original compound and holds the wood in its new shape. 

Fun Fact about Lignin

Because of its chemical compound lignin is actually being researched as an alternative to petroleum. It is carbon neutral, renewable and could help to reduce the environmental impact of petroleum products. 

Stretching and Compression of Bent Wood

Bending wood is difficult because it requires stretching of the fibers on the outer end of the piece and immense compression of fibers on the inner edge.  This is why bending wood can make it crack, splinter and break. Lignin is incredible in that it stretches just enough and compresses to a point where the wood fibers can be manipulated into almost any shape. It really is a scientific wonder. 

What Types of Wood Can Be Steamed & Bent?

Hardwoods are recommended as the best types of wood for steam bending. Some temperate-zone hardwoods that are popular for steam bending include white and red oak, elm, hickory, ash, cherry, maple and walnut.

Materials Needed for Wood Steaming

Wood steaming does require some specific types of machines and materials. The most important is a steam box. Steam boxes can be custom-made and can come in many shapes and sizes. 

Depending on the length and width of the wood, the type of project or the number of pieces you want to steam at once, steam boxes can look very different. This box is where the wood is placed and a steam generator pumps in hot steam to heat the wood and add moisture to the box. 

Aside from the steam box and wood itself, a bending form is used to pend the wood against and fix it into the desired shape. Some bending forms are used along with a strip of metal to help prevent the wood from bowing or blowing out against the form. Clamps are used to secure the wood to the bending form.  

Benefits of Wood Steaming

Steam bending is popular partly because it’s much more economical in the long run. Since you use one piece of wood and no glue, it also produces less waste over time. There's no cutting, fitting, gluing, measuring or sawing needed. The singular continual use of a piece of wood means no broken wood grains, adding to the look and design of a project. 

Steamed wood projects can actually be stronger than cut and glued wood. Because the fibers aren’t broken and artificially attached, the wood retains its original structure. The likelihood of a steamed wood board breaking is lower than one that has been pieced together with glue.

How Long Do You Need to Steam Wood For?

The general rule in steam bending is to steam the wood for one hour per inch of thickness. The width of the wood doesn’t really matter. 

Safety Precautions When Steam Bending

When working with heat of any kind, there are certain things to be aware of for safety’s sake. Steam is incredibly hot and can cause serious burns. Caution should be taken when opening up the steam box to prevent any burns on arms, face or hands. 

Under-steamed wood will not be as pliable and could break or snap under pressure. If the wood is giving you resistance and doesn’t want to bend, place it back in the steam box for an extra hour or two. Trying to force the wood could cause it to break and bounce back at you. 

Removing Steam Bent Wood from Form

Depending on the thickness, width and size of the wood, it will take different periods of time to dry out. Some will dry in a few hours, some will take a day or more. It’s better to err on the side for longer to reduce the risk of removing the wood too early. 

If removed from the form before fully dried, the shape will change. Try to plan your projects to allow for steamed wood to be left on the form for a minimum of 24 hours, just to be safe.

Steaming Wood: A Woodworker’s Paradise

This seemingly simple process allows woodworkers to craft beautiful and unique products. While wood has been used in construction for thousands of years, steam bending is proof that we are far from bored of it.