You’ll be in a better position to use this fantastic natural resource as you get more insight into wood movement (see Part 1). While we can’t stop wood from naturally expanding and contracting, we can prepare for that movement and take measures to lessen any issues that may arise as a result.
The size of the gap you leave between decking boards will vary depending on the temperature, location, and time of year in which you install the boards, because lumber constantly expands and contracts in response to the surrounding moisture levels. The boards won’t expand or shrink in every direction, though.
Think of a bundle of straws that has been frozen after being filled with water. What areas of the straws will the water come off of as they start to thaw? Even though the straws can “sweat” or condense, the water will primarily escape through the ends of the straws. The moisture will also escape through the ends of lumber. Because of this, even while the middle retains a larger volume of moisture, the ends of the board will get dry. Warping, as well as bending and cupping, can result from the variations in moisture levels between the ends and the middle of a particular board.
Correct Drying Techniques
When moving lumber from one location to another during times of acclimatization, you can take preventative measures to lessen the likelihood of such undesirable effects of uneven drying. One approach to doing this is by not leaving lumber out in direct sunlight, where moisture loss may happen more quickly. Applying end sealer to cut boards is a second method to lessen uneven drying. A third option is to stack the timber in a well-ventilated area and “sticker” it, inserting pieces between the boards to allow air to pass through the stack. Allowing enough time for timber to adapt to new surroundings prior to installation is the fourth and, arguably, most crucial approach to encouraging even drying.
Leveraging a Kiln for Drying
The majority of the time, the lumber you receive on your construction site will already have undergone kiln drying, so the lumber supplier has already done the bulk of the work for you. The highest level of stability can be seen in lumber after kiln drying because of its homogeneous (i.e. equal throughout) moisture content. Case hardening won’t happen as a result of proper kiln drying; instead, the lumber will still be able to move as it takes in and releases moisture, just not as quickly or as much. Kiln drying may not always be the ideal option for decking lumber, though.
You must account for wood movement when constructing indoor flooring, an outdoor deck, or even trim around windows or doors since wood movement is almost guaranteed to happen in some measure. Movement is a component of what makes wood what it is because it is an organic substance.
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