How do I stop a green wood carving cracking as it dries?
Cracks come from one part drying faster than another. The four things that cause that — end grain, uneven walls, the pith, and heat — and how to remove each.
- Difficulty
- intermediate
- Time
- 15 min
- Read
- 3 min
Short answer
Cracks form when the outside shrinks while the inside is still wet. Keep the walls an even thickness, avoid the pith entirely, seal the end grain if the piece is thick, and dry slowly in a paper bag with its own shavings, somewhere cool. Never dry a carving on a radiator, in sunlight or in an airing cupboard.
Wood does not crack because it dries. It cracks because it dries unevenly — the surface shrinks around a core that has not shrunk yet, and something has to give. Every technique for preventing cracks is a way of making the drying more even, whether that is thinning the walls or slowing the whole thing down.
Step by step
- Remove the pith.The very centre of a log has the wood's shortest rings around it and it will split radially as it dries in almost every species. Split the log through the pith and work each half, or hollow the pith out.
- Even the wall thickness out before drying.A thin section beside a thick one dries at very different rates and the boundary is where the crack forms. On a bowl or a spoon, get the walls consistent while the wood is still wet and easy to cut.
- Slow the drying with a paper bag.Put the piece in a paper bag with its own shavings and fold the top over. The shavings hold humidity around the piece and the paper lets moisture out gradually. This one trick prevents most cracking.
- Keep it cool and out of draughts.A shed floor, a cellar or a cool room. Radiators, sunny windowsills, cars and airing cupboards all crack green wood reliably.
- Seal end grain on anything thick.End grain loses moisture many times faster than the sides, which is why cracks nearly always start there. Wax, PVA, old paint or a proprietary end sealer on any exposed end grain of a blank you are storing.
- Rough out oversize and finish after drying, on larger pieces.Carve to within a few millimetres, dry it, then take the final cuts. Any small checks that appear on the surface are then removed by the finishing cuts.
- Weigh it if you want to know when it is dry.Weigh the piece every few days. When the weight stops falling, it has reached equilibrium with the room. It is a more reliable test than any amount of guessing.
- Accept some movement.A green-carved bowl will go slightly oval, and a spoon will shift a little. That is the character of the technique, not a fault. Only cracks are failures.
Tips
- Sealing a whole carving in wax or varnish does not stop cracking — it traps moisture in and can make it worse. What you want is slow and even, not sealed.
- Store unworked green blanks in a bucket of water or a sealed bag if you cannot get to them quickly. They will keep for weeks.
- Species vary a great deal. Fruit woods and oak crack readily; willow, lime and birch are much more forgiving.
If it doesn't work
Radial cracks from the centre outwards
Cause: The pith was left in the blank — Fix: No repair. Split the pith out of the next blank; it is the most reliable cause of cracking there is.
Cracks at the rim of a bowl or the end of a spoon
Cause: End grain drying much faster than the rest — Fix: Seal end grain on blanks, and slow the drying with a bag. Existing fine cracks can sometimes be stabilised with thin glue.
A crack appeared where a thick part meets a thin one
Cause: Uneven wall thickness — Fix: Thin the walls evenly while the piece is still green. There is no fix once it has cracked.
The piece cracked within a day of finishing carving
Cause: Left in a warm, dry or draughty place — Fix: Bag it as soon as you stop carving, even overnight. A green carving left on a bench in a heated room can check within hours.
Questions people ask
Can I dry a green carving in the microwave?
It is done, in very short bursts at low power with long rests between, and it works for small thin items. It also splits a great many pieces and can scorch from the inside. Slow air drying in a bag is far more reliable.
Will the crack get worse?
Usually it stabilises once the piece reaches equilibrium, then opens and closes slightly with the seasons. A crack in a functional item like a spoon bowl makes it unhygienic and it should not be used for food.