Sapwood and Heartwood – Know the Differences
To achieve high-quality woodworking, knowledge about wood is a must. Projects can succeed or fail based on which part of a tree is used. In particular, it’s important to know the difference between heartwood and sapwood.
The Parts of a Tree
Knowing how a tree grows sheds light on which part of a tree is best for your woodworking project. A tree trunk is composed of the following basic parts, listed in order beginning with the outer layer:
- The bark is dead tissue; and its function is to protect the tree from weather, insects, disease, fire, and injury.
- The phloem is a thin layer comprised of living cells, and its basic function is to transport food around the tree.
- The cambium is living tissue. This very thin layer of a tree produces both new phloem on one side and new xylem on the other.
- The largest part of a trunk is the xylem, which is composed of both sapwood and heartwood.
What is Sapwood
Sapwood is new wood and is like a pipeline that moves water through the tree up to the leaves. Essentially the working component of a tree, sapwood transports water and sap similar to the way blood flows through our veins, capillaries, and arteries.
You can usually spot the difference between the two distinct parts of the tree’s xylem if you were to view a crosscut of a mature hardwood tree’s trunk. Once you remove the comparatively thin outer layers, the tree is essentially made up of sapwood, which is lighter colored wood, and heartwood, which is darker in color.
What is Heartwood
The central, strong pillar of a tree is heartwood. As new rings of sapwood grow, the inner cells are put out of commission and become heartwood. Although this portion of the tree is dead or retired sapwood, it doesn’t decay. As long as the tree’s outer layers are intact, heartwood remains strong.
What occurs as moisture is no longer transported through the straw-like cells, the pores in Heartwood are filled with organic material. The presence of chemicals called extractives causes the cell walls in heartwood to change color. Extractives are what create the rich color and unique character in the heartwood.
The functional beauty of heartwood for a woodworker is threefold. First, it’s significantly less susceptible to fungus. Secondly, heartwood contains far less moisture than sapwood and will have far less shrinkage when it’s dried. Thirdly, heartwood becomes in some ways as strong as steel as the fibers are bound together.
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Regardless of whether the woodworker is working with sapwood or heartwood, the correct moisture content of the wood is critical to meet the demands for the end use of the product being made. A high-quality, accurate moisture meter is, therefore, a must for the serious woodworker.
Both heartwood and sapwood hold moisture. Before drying, heartwood holds far less moisture than sapwood1, but you need to account for the moisture content (MC) in both types of wood. If the MC percentage is too low or high, your work could be damaged as the wood shrinks or expands in the process of equilibrating with its surroundings.
In most cases, you want the wood to reach an MC between 6% to 8% before you start working with it. That’s the suitable MC for most indoor spaces with the HVAC operating. A pinless moisture meter will deliver fast and accurate MC readings without damaging the wood. Take multiple readings across the wood to get the most complete picture of the wood’s MC before you start working with it.
As Sales Manager for Wagner Meters, Ron has more than 35 years of experience with instrumentation and measurement systems in different industries. In previous positions, he has served as Regional Sales Manager, Product and Projects Manager, and Sales Manager for manufacturers involved in measurement instrumentation.
Last updated on September 21st, 2021