How to Steam Wood

Steaming is an effective method of softening or plasticizing wood so that it may be molded for craftsman and industrial applications, such as the manufacture of furniture and boat parts. Experts approach this method differently, depending on the type of wood grain and the quantity of the material involved in the project. The timed process involves placing wood scraps in a box, which is supplied with heat via a steam generator. Once the wood pieces are steamed, they are pliable and immediately ready to be shaped during the second part of the steam bending process, with the aid of a jig and other shaping equipment.

Wood Steaming Applications:

• Housing Construction: chair parts and staircase banisters

• Boat and ship construction: eg, canoes

• Musical instruments, cello

• Basket rims
  

Wood Selection and Pre-treatment

Generally, wood should be moist before initiating the steaming process, as damp wood is most effective with heat transfer. Some woods already have high moisture content while others will need to be pre-soaked. As a general rule, hardwoods are well-suited for steaming and bending than softwoods. Experts note that cross-grained wood is more susceptible to cracks and overall bending failure than straight-grained wood, which should be noted before processing the wood. Greenwood, which has a moist composition, is the standard recommendation for steaming and bending, though different applications require hardwood selection. Bending qualities of various hardwoods were tested by the U.S. Forest Service and the results show that white oak, hackberry and  red oak were ranked as the best woods, while soft maple, yellow-poplar and hard maple were ranked as the least compatible with the steam bending process.

Steam boxes may be constructed from wood or from PVC pipe and must completely encase the wood scraps so that the steam may saturate the entire length of the lumber. Some professionals prefer to construct racks within the box for the individual pieces of wood to rest on, though this is not mandatory. While the box should be tight enough to hold steam, it should also include an opening, like a drilled hole, so that the steam may flow around the wood. Openings are also crucial so that the steam does not become volatile. Additionally, many steam boxes feature a door so that pieces may be added and removed when necessary. Some professionals opt to use a soft material like a rag, which acts as a door during the process.

Steam generators can be a commercial appliance like a teakettle, pressure cooker or metal gas can. The generator, which can be found in most hardware stores, should be unused and clean. This tool must be able to link with a hose that will connect to a hole in the steam box. Do-it-yourself artisans suggest cutting a hole at the top of the generator (of one doesn’t already exist) and fastening the hose with large nuts. The hose may be attached to the mouth of the tea kettle, but must be fitted tightly and properly. Keep in mind that the wood should only be placed in the box when there is a sufficient amount of water in the steam box. Interrupted flow of the steam will greatly affect the heating process.

Place the moist scraps of wood in the steam box. Some professionals advise soaking the lumber at least a day before heating.
Carefully monitor the material and the time using a thermometer and timer. Ensure that there is an opening for the steam to flow over and around the wood pieces.
Insert a hose or other attachment on the steam generator and connect the hose to an opening in the steam container.
Let the steam saturate for the specific amount of time.
Remove the wood promptly for the second part of the process: bending.