All lumber, regardless of the species, is cut from logs on a sawmill. Fresh lumber has a heavy moisture content and is called green lumber. Green lumber can have as much as 200 percent moisture content depending on the time of year for harvest. Improperly drying green lumber can result in rotted, cracked or warped boards. Walnut is especially prone to cracking and warping during the drying process.
Plenty of Air
When lumber is dried, it is placed into stacks. Between each layer of boards, a smaller board called a sticker is used. The size of a sticker is 1 inch by 1 inch and 4 feet long. The sticker keeps the boards from touching each other and creates an air space between the layers. Typically the stack of boards is made into piles 4 feet wide by 8 feet long, and 8 feet high. The stickers are inserted between each row and run across the boards perpendicularly. The piles of stacked lumber can be either kiln-dried or left in open air to dry. Kiln-drying lumber takes special equipment and can be very expensive. Air drying a pile of walnut lumber takes extra work, but can be done if space is available for the pile.
Keep it Covered
Keep the pile out of direct sunlight with plenty of air circulation. The stack of walnut lumber can be placed under a roof enclosure as long as airflow is not impeded. A fully enclosed shed may require placing window-box-type fans at the end of the pile to move air through the lumber. Moisture will collect on the underside of the boards if air circulation is not provided.
High-humidity days may also cause a fungus to form on the boards. The fungus can work its way into the boards and stain them.
Piles stacked outdoors need to have a large enough covering over them to protect all the boards from sun discoloration and rain. The cover must also allow the air to circulate throughout the pile.
Other stacks of lumber must not be placed too close, as this can also impede airflow.
Most all lumber, walnut particularly, will dry out through the ends of the boards. Boards that dry out too quickly will crack or check at the ends of the boards. This is caused by moisture leaving the wood and shrinking the cell walls of the lumber. When this happens, the wood shrinks unevenly, causing the cracks. Some checks or cracks in the boards can ruin the wood with extensive defects.
Apply a sealant to the ends of the boards immediately after cutting from the sawmill. Latex paint or a wax covering will seal the ends of the boards' cells. This causes the moisture to move through the surface of the boards instead of the short ends.
Uneven drying can also cause the boards to warp. Typically this happens to thinner boards placed at the top of the pile. Lay lighter, thinner boards near the bottom. Place heavier, thicker boards on top. The weight will keep the smaller boards from warping.
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