Heartwood and Sapwood

Heartwood and sapwood are parts of wood with different properties. Sapwood is wood from the edges of trees, while heartwood is obtained from the inside of the trees, and in terms of their properties, both have significant differences. In the woodworking industry, the heartwood is the wood part that has the maximum value. The heartwood is the wood with its maximum strength. It is strong, dense, and durable. The heartwood can be clearly different from the sapwood according to its properties. 

 

wood anatomy

If we cut a tree on a cross-section, we will see that there are many circular layers in the wood log. The circles in the wood actually show the annual living of the tree. In his lifetime, the trees grow in the tangential and radial directions. The axial growth occurs with the formation of wood cells at the tip of the tree, including the formation of the branches and new tips. While the radial growth occurs with the development of cambium. Cambium is the outer part of the wood log, where the new wood cells are formed. The wood cells from the cambium are growing to be the young wood of the tree, which is called the sapwood. The sapwood will continue to grow to become the heartwood, the old wood of the tree where the wood cell has stopped growing and the wood already reaches its maximum strength. The life circle from the cambium to the sapwood and ending with the heartwood is fulfilled in one year. Then actually we can see the age of the wood by viewing the wood ring.

Here are the important properties of the sapwood and heartwood according to the woodworking industry.

• The hardness and strength.

Heartwood is part of the tree that already has the maximum strength. During its lifetime, its main function is to support the tree to keep standing. It holds the tree against the wind, rain, and other natural disturbances. It is physically tough, strong, dense, and durable. Most of the heartwood is also highly resistant to insects and fungi.
While the sapwood functions to bring the water and nutrition from the soil to the leaves. Sapwood is physically soft, has less density, is weak, and is less durable. The sapwood of any type of wood is vulnerable to getting attacked by insects and fungi.

• The grain and pore

Heartwood also gives the best appearance to the grain and pores. He has the maximum appearance according to the pores and grain. The heartwood shows a strong character of pores and grain in appearance and texture. In the premium woods, such as rosewood, sonokeling, and walnut, we can see the black stripes very clearly on the heartwood. In another wood such as mindi, teak, or mahogany, then we can see the grain and pore texture are very strong at the heartwood.
Meanwhile, the sapwood usually has a vague and soft grain pattern. Sapwood in rosewood, sonokeling, and walnut seems to be the soft pattern; there are no or fewer black stripes in the wood. The sapwood for mahogany, teak, and mindi will also display the shallower grain and pore texture.

• Base color.

Heartwood can differ from sapwood in its basic color. In some timbers, such as rosewood, walnut, and sonokeling, the difference in the wood base color could be so contrasting. But for wood with a light base color, such as maple, teak, sengon, or pine, the difference in color between sapwood and heartwood will be less contrasting.

• Stability.

Although the wood properties are highly dependent on the type of wood, generally the heartwood is much more stable than the softwood. The heartwood is less permeable, less hygroscopic, and has less contraction according to the wood moisture content changes.

The utilization of the sapwood.

a mix of sapwood and softwood in the furniture

The use of the heartwood in the woodworking industry cannot be avoided. When we mention the wood properties in woodworking, it always refers to the heartwood. Meanwhile, the sapwood is the cheap part of the wood log. In the past, when the wood was abundantly available, the sapwood was usually discharged or separated and sold at a cheaper price. But this time, when the wood price is expensive, the sapwood is also much used.
To prevent the insects and fungi from attacking, the treatment with the anti-insect repellent or antifungal is highly recommended. With the consumption of wood that keeps increasing and more wood types being used, chemical treatment and preservation are already considered the standard procedures in wood utilization.

Meanwhile, variation of the base color and difference in color between sapwood and heartwood could be anticipated by the finishing technique. With the proper stain and application technique, we can handle the variation of wood color to make the uniform color of the final product. The light color of the sapwood even could be an advantage because it can generate the finishing with light color if needed.
The sapwood and heartwood can be mixed and laminated to make a big and wide panel. With proper gluing, the laminated wood is more stable and stronger than 1 piece of wood plank.

The veneering technology has also made the utilization of sapwood more optimal. The sapwood veneer can be separated and sold at a cheaper price. The lesser strength of the sapwood would not be a problem at the veneer since it is only a thin layer; the structure is built by its core. The soft wood grain and pore pattern could be an advantage because it can produce a softer appearance. The light basic color sapwood is also an advantage because it will provide higher flexibility in the final color choice.