Carving Green Wood - Canadian Woodworking Magazine

Carving Green Wood

Illustration by Mike Del Rizzo

I have had black walnut that was stored in a barn, out of any weather, for more than 20 years. When I started to carve it, the wood was still wet only 2" from the outside. My method is to get rid of as much wood as possible while it is wet, because you don't care about that part of the wood anyway. The more wood you remove the less water there will be in the log and the less likelihood it will crack. Then, during the carving process, the task remains to control the distribution of water inside the wood.

The cracking of wet wood is reasonably easy to prevent if one understands why it happens. In this regard, it is interesting to note that most carvers know to seal the end of logs to inhibit cracking. Perhaps it isn't clear why this helps. Consider a piece of wood as a container filled with water. If the container shrinks too much, the water inside will burst the sides or spill over. Think of the outside of a log as that container. If it dries, it will shrink. If it shrinks too much, the volume inside the log (which is still swollen with water) will break the outside. That is, the wood will crack. To prevent this undesirable drying, shrinking and cracking, the simple solution is to keep the outside of the log wet. In other words, keep the water in the wood.

Many carvers go to great lengths to avoid using green, freshly cut wood. A common concern is cracking or checking because the wood is wet. Instead, carvers will pay for kiln-dried wood and either use it in small blocks or laminate blocks together for a larger project. In my view, both these options have a down side: the size of available kiln-dried wood dictates the size of the project; and, large laminated blocks preclude the more effective use of grain possible with wood in-the-round. To have the most options, a carver should learn how to carve green wood.

Seal the ends

Un-sealed wood cracks

Mist and cover work between carving sessions

To control the wood's moisture content, one is actually controlling the rate of evaporation. As I noted earlier, if the wood dries too quickly, the outer layer shrinks too much. Then, because the inner wood is swollen with water, it forces the outer layer to crack. During the carving process, some water will always evaporate. Using a spray bottle periodically to dampen the piece will inhibit rapid moisture loss. At the end of each carving session, the work-in-progress should be sprayed lightly and covered with a plastic bag. The water in the wood will always seek a balance of even distribution. Enclosing the carving in a bag gives moisture deep inside the wood time to migrate toward the drier outside. If progress is going to be delayed for a lengthy period, you can also coat the piece with a light oil, even mineral oil will do. Long delays are not a problem; however, wood enclosed too long may grow mold. It is a good idea to remove the plastic bag every day for a short period, then replace it over the piece.

When your carving is complete, the routine of enclosing the piece for a prolonged period (overnight or throughout the day), turning the plastic bag inside out, and replacing the cover should be continued. It is also useful if the enclosed carving can be placed in a sunny location. By doing this, one is essentially creating a solar kiln in which the carving is being dried gradually.

Despite all the precautions one might take, some cracking may still occur. If so, to minimize the problem, soak the area by placing a damp cloth over the crack. Sometimes, this action might not be possible while you are carving. An alternative is to cover the crack with a piece of masking tape thus preventing more moisture loss from inside the crack. At the end of the day, soak the spot with water. The water applied on the outside, and the water migrating from the inside will usually swell the wood and close the crack.

When a crack persists at the end of a project, it should be filled to prevent moisture from evaporating inside the crack and causing it to expand. NEVER fill a crack with a hard substance like epoxy. Such materials merely prevent the crack from ever closing. Instead, use wax. I have a box of children's crayons (128 colours) from which to choose the exact colour of the wood. It is even possible to match wood grain if desired. One can fill the crack with the wax just like drawing.

After the carving is complete and a finish is applied, the moisture content in the wood will be trapped. Some evaporation and respiration will always occur with wood; however, the moisture content will seek a balance throughout the wood and cracks will close naturally. When they do, the wax will be squeezed out and can be scraped off – something than can never happen with epoxy or glue.

Cover a crack with tape

Fill cracks with wax not epoxy

'The Boxer' carved from green wood

By learning to carve green wood, the cost of buying kiln-dried wood can be avoided, the size of a project need not be confined by the size of the block, and the beauty of the wood grain can be utilized most effectively. Cracking, and its prevention, is all about controlling moisture loss and the distribution of moisture in the wood. With this knowledge, you can now use all of the wood that you have accumulated, and have been waiting to use.

DAVID BRUCE JOHNSON