![]() ![]() If you look at the end of a piece of wood, you will be able to see lines which are the so-called age rings of trees. Wood that is harvested from near the center of the trunk will display less movement than wood that is harvested from the edge of the trunk. Wood shrinks most in the direction of the annual growth rings (tangentially), and only half as much across the rings (radially, or from the centre of the tree to the outer edge). With a little bit of knowledge, you can predict the degree of wood movement, and take appropriate action to accomodate the movement. Wood that expands and contracts due to changes in moisture content will do so along predictable lines. Just like a sponge, the wood will absorb moisture from the air and expand, or give up moisture and shrink. Current practice involves using a kiln to dry wood to an even lower moisture content, approximately 7-10% moisture content.īut once you purchase that 2×4, its moisture content will not remain constant. Traditionally, these blanks are air dried to approximately 15% moisture content, giving up its moisture to the atmosphere. This raw wood is then stripped of bark and branches, and then cut into various sized blanks. Wood that is freshly cut is referred to as green wood or wet wood, referring to its high moisture content (40% or more!) When this tree trunk is cut down, the sap stops flowing, but the sap remains in the trunk. As a living tree, the trunk of the tree provided a mechanism to transport water (in the form of sap) from the roots to the leaves. The 2×4 that you buy at the lumberyard began as a living tree.
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