Hardwood Floors FAQs | How Are Knots, Sapwood, and Heartwood Formed?

Natural formations give hardwood floors their trademark character and warmth. But consumers wonder how those knots, sapwood and heartwood are formed and whether or not these elements affect the quality of your flooring. Let’s dig deeper into the formation of wood to understand hardwood flooring on a whole new level.

What is Sapwood?

Wood is categorized as sapwood or heartwood, depending on the formation and location within the tree. Sapwood is lighter in color than heartwood, and is formed within the outer layers of a tree. It is also softer than heartwood, which could have an effect on wood flooring durability.

Younger trees are made almost entirely of sapwood, since it is formed first. Heartwood, the denser, stronger center of the tree, forms from sapwood. As the tree ages, sapwood closer to the center becomes ineffective and resins form within the fibers. This transition creates heartwood.

Some trees or species have more heartwood than others, and some form heartwood earlier in their lifespan. Where a tree is planted also makes a difference, as higher leaf counts create less heartwood. Therefore, trees growing in a dense forest may contain more heartwood than those growing in the open, with a full crown of leaves.

What About Hardwood Flooring – Does It Contain Sapwood or Heartwood?

Depending on the type of hardwood purchased, it will contain a certain percentage of both sapwood and heartwood. High grades of wood contain less sapwood, although these grades are less likely to be used for hardwood flooring. Even “select or better,” the highest grade of wood used in the flooring industry, contains both sapwood and heartwood.

In many cases, heartwood presents a darker shade or color than sapwood from the same tree. But do not assume that light colored wood floors are made from weaker sapwood—the wood coloring depends on the species and where the tree was grown. Slight color variations in the wood are considered attractive and hardwood manufacturers market this characteristic on purpose.

How Are Knots Formed and Do Knots Weaken Wood Floors?

Wood color variations represent the transition from sapwood to heartwood, but knots are an entirely different matter. Knots present small ovals, outlined with resin and standing out from the grain. Formed at the base of side branches on a tree, knots may also stem from dormant buds on a tree.

Many associate knots with weakness, although that may not always be the case. In structural lumber, the location and size of a knot dictates how much that knot affects strength. In hardwood flooring applications, a knot affects the appearance and has little to do with durability and strength.

Select or better lumber contains the occasional knot and those knots are limited in size—nothing larger than 10mm will pass through the grading process. On the other end of the spectrum, rustic graded lumber used for wide planked products contain knots of varying sizes.

Knots are normally filled and treated to prevent bleeding around the knot, which tends to alter the stain or finish. Rustic styles of hardwood may contain open knots. Ask your wood flooring retailer for details, as each manufacturer offers a slightly different look.

Wood variations make this building material special and attractive. Color variations happen naturally as sapwood transforms into heartwood and dormant buds or side branches create knots of various sizes. All of these characteristics come together to make your flooring unique and warm.