When working with wood, it is often desirable to bend and shape it to create curved forms for furniture, instruments, barrels, and other projects. Bending wood requires some preparation, as wood does not easily bend without some help. One of the most common methods of softening and preparing wood for bending is to soak it in water. But how long should you soak wood before bending it? The soaking time can vary quite a bit depending on the type of wood and the degree of bend required.
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What Does Soaking Do?
Soaking wood in water serves multiple important functions in preparing it for bending:
- Softens the lignin – Lignin is a compound in wood that acts like a natural plastic binder. When lignin absorbs water, it becomes more pliable and flexible. This allows the wood cells to move more freely when bent.
- Swells cells – Water causes the wood cells to swell in size. This swelling helps make the cells more supple and able to compress, stretch, and move around each other when bent.
- Adds weight – The saturated wood gains weight as it soaks up water. This extra weight helps bend the wood down against its natural stiffness.
- Equalizes moisture – Soaking evens out the moisture content across the wood. This equalization prevents cracking or splitting during bending.
In short, soaking wood plasticizes the lignin, swells the cells, adds weight, and equalizes moisture content to allow the wood to bend without breaking. The longer the soak time, the more profound these effects become.
Factors That Affect Soak Time
Several key factors come into play when determining the ideal soak time for bending wood:
Wood Species
Some species of wood are naturally more pliable than others. Dense hardwoods like oak, hickory, and ash require longer soaking than more flexible woods such as redwood, pine, or spruce. Here are typical minimum soak times for some common wood species:
| Wood Species | Minimum Soak Time |
|---|---|
| Basswood | 2 hours |
| Redwood | 4 hours |
| White pine | 8 hours |
| Oak | 24 hours |
| Maple | 48 hours |
Thickness of Wood
Thicker pieces of wood require longer soaking than thinner pieces. A good rule of thumb is to soak wood for 1 hour per 1/8 inch (3 mm) of thickness. So a piece of oak 1 inch (25 mm) thick would soak for about 8 hours minimum.
Degree of Bend
The tighter the bend radius, the longer the required soak time. Gentle sweeping bends may only need 24 hours of soaking. But extreme bends with tight radii, like bending oak strips for chair backs, may require soaking for 3 days or more.
Method of Bending
Some bending methods are more stressful on the wood fibers than others. Steam bending relies solely on the softened wood flexing around a form, requiring thorough soaking. Bending with laminations puts less tension on each individual layer, allowing somewhat shorter soak times.
Temperature of Water
Warm water accelerates the softening process by swelling the wood cells more quickly. Heating the water to 100-180°F (38-82°C) can decrease soak times by 30% or more compared to room temperature water.
Guidelines for Soak Times
Taking all of these factors into account, here are some general guidelines for minimum soaking times:
- Softwoods (pine, cedar, redwood) – 2 to 12 hours
- Medium hardwoods (cherry, walnut, elm) – 12 to 24 hours
- Hard hardwoods (oak, maple, ash) – 24 to 48 hours
- Dense exotic hardwoods (lignum vitae, bubinga) – 48 to 72 hours
- Thin bend pieces (1/8″ or less) – Halve the times above
- Gentle bends – Minimum times or less
- Extreme bends – Double the times above
- Steam bending – Double the times above
- Heated water – Reduce times above by 30%
These soak times are minimums only. For dense woods and extreme bends, pre-bending tests are recommended to determine if longer soak times are needed. So err on the side of longer soaking when in doubt.
Tips for Effective Soaking
Follow these tips for the best results when soaking wood for bending:
- Submerge the wood fully underwater. Weight it down if it wants to float.
- Change the water every 12-24 hours to prevent it from getting too acidic.
- Keep the end grain sealed with paint or wax to minimize water absorption.
- Wrap wood in plastic wrap or a wet towel if removing it temporarily from the bath.
- Soak in a tub, trough, or even a creek – whatever fits the wood.
- Pre-seal woods like oak that are prone to staining.
- Use warm water for faster soaking if desired.
- Test bend a scrap piece first before removing wood from soak.
When is Wood Ready for Bending?
Determining precisely when wood is ready for bending takes some judgment. Here are a few ways to test if it’s soaked long enough:
Scrape Test
Use a thumbnail or knife to scrape away a little wood. If it scrapes easily leaving a mark, it’s likely ready. If it still seems hard, soak longer.
Bend Test
Try bending a corner. If it bends easily without cracking, it’s soaked enough. If it barely bends or cracks, keep soaking.
Moisture Meter
Use a wood moisture meter to check the moisture content. Softwoods should reach 30-35% moisture, hardwoods 40-45% for bending.
Sample Bend
Bend a scrap piece using the same technique. If it bends well without damage, the rest should be ready.
Dangers of Over Soaking
Can wood be soaked too long for bending? Over soaking wood can lead to a few issues:
- Weakening – Extremely saturated wood can become mushy and lose some strength and elasticity.
- Staining – Prolonged water exposure can cause staining or rot in some woods.
- Checking – Very wet wood dries out too fast after bending, risking checks and cracks.
- Bacteria – Long soaks allow mold, fungus, and bacteria to start growing in the water and on wood.
However, the dangers of over soaking are generally not huge for most bending projects. The exceptions are projects where strength is paramount, like laminated boat planks or building components. For furniture, instruments, barrels and similar applications, erring on the side of a slightly longer soak is generally better than not soaking quite long enough.
Conclusion
Soaking wood prior to bending allows the fibers to become pliable so they can move without breaking when shaped. Use 1 hour per 1/8 inch of thickness as a basic soak time guide. Adjust this up or down based on wood species, bend tightness, technique, and water temperature. While over soaking isn’t ideal, it’s much better than inadequate soaking which can result in wood that cracks and breaks when bent. Test scraps first, and give the wood ample time in the water for best bending results.