If you're a casual woodworker or Pinterest project professional, you've likely read the words "kiln dried wood" when searching for materials for your DIY projects. If you've visited your local lumber yard, chances are all the wood in stock is kiln dried-- it's industry standard for a number of reasons. If you're lucky enough to live near a local, live edge millyard, then you might be given the option to purchase either kiln dried or green wood. So what's the difference and what is best for your project?
Trees naturally contain a lot of water, it's what makes them so vital to our ecosystem. One large tree can lift up to 100 gallons of water out of the ground and discharge it into the air in a day (NC State University). That's pretty impressive! So when a tree becomes a log, it only makes sense that there's still a significant amount of water in its fibers.
We measure this water as moisture content (MC). Typically, newly sawed wood will have a MC of 30-100%. For wood to be stable enough to be used for construction, it needs to have a MC of 9-14%. For furniture or hardwood floors, we really want our MC to be 9% or less.
So what does the MC have to do with durability? Water is much more susceptible to temperature changes. Green wood (MC of over 14%), is much more likely to warp and crack over time as the water expands and contracts with the temperature changes.
Back in the day, it was far less important whether or not a slab of wood was freshly cut and full of moisture or nice and dry. Our homes were poorly insulated and unevenly heated, allowing the moisture in the wood to self regulate. Now, with high quality, insulated homes equipped with central heating and cooling systems, our homes maintain a stable indoor temperature and moisture level. That means the wood we use in our home will be more susceptible to cracking and breaking if it has moisture in it.
If you're looking to make a bench for your front porch or perhaps a natural playground of stepping stumps and balance beams for your backyard, then our lovely PNW weather won't be too much of a concern for green wood.
However, if you want to ensure that your beautiful live-edge dining room table or fireplace mantel stays in tip-top shape, you will want to make sure you use a piece of wood that has been dried properly.
There are two methods for drying wood: air drying and kiln drying. Air drying is a traditional process that requires patience and space: stacking cut wood, ensuring even airflow, protection from fungi and rot and also protection from direction sunlight that will dry out wood too quickly. These stacks take years to dry, depending on your local climate conditions.
Kiln drying on the other hand, takes months-- not years. And although the process takes more skill and know-how, the results are much stronger, drier wood suitable for any indoor project. There is some loss of product when kiln drying. Since the process is so much faster, often 10% of the cut pieces crack and are deemed less valuable than they were prior to entering the kiln. For these two reasons (increased durability paired with potential product loss), kiln dried wood is often much more expensive. But that extra cost is worth the value when you're putting your hard earned time and money into an exceptional project!