Thread: Steaming OLD wood

Welcome to the forum. For best results timber should be carrying moisture prior to being steamed. This helps with heat transfer. Green timber is much easier to steam than dry for this reason. Oak is a good steaming wood but should be well soaked prior to being steamed.

I find dry wood even though you leave it to soak for a week still has less than10 percent chance of bending successfully, you will also need sprung steel strap to hold the outer surface and stop the fibres from springing out. Blackwood is the most successful wood I have used for steam bending for windsor chairs.

Depending on the wood, a week wouldn't be long enough. More like a month.

Most successful steam bending of timber is done when the wood is green. This is due to the lignin in the timber being at it's most abundant.

Lignin is a protein that binds or glues the cellulose structure of the timber together, and it is suggested that as wood dries it loses lignin, not moisture. Therefore, soaking dried timber is somewhat of a futile activity as it is not possible to replace that which has been lost...lignin. It will however contribute to the steaming process as it vaporises once heat is introduced.

Over time, lignin can also be broken down by oxygen and UV radiation. This is evident in what we would regard as heavily weathered timber. Sealing or finishing dried timber is what slows or prevents it from breaking down any further.

When steam bending timber, cells soften or plasticise and are then able to be compressed. The lignin is also softened during the process and then re-bond the compressed cells as the timbers cools or sets to it's form.

Different timber species have differing cell structures and lignin levels. This is why some species are more suitable than others for bending. Due to the differences in the cell structures between species, some timber will experience more spring back once removed from a form as it's cells are more resistant to the level of compression trying to be achieved. Most forms are built beyond the required radius to accommodate this.

Generally speaking, dried timber is better suited to cold forming. This is where we created a series of strips or laminations and glue between the layers before placing them in the form. This method is usually more successful because modern glues (if correctly selected for the task) are stronger and have more rigidity than timber lignin.

Oak (American/Red/White) is otherwise regarded as an excellent timber for steam bending.

Craig

Thank you all for your input. Sounds like that idea is a bust! Back to the drawing board.
Martin