Hardwood Floors: The Differences Between Heartwood and Sapwood

If you look at the end of a log, you may notice that there is always a lighter ring surrounding a dark inner ring. Sometimes this distinction is obvious, and other times it's hard to distinguish the difference.

The light outer ring is called the sapwood, and contains a tree's living cells; all wood starts as sapwood. As a tree ages, its cells die and it becomes inactive and non-functional. This is the darker, inner core of the tree and is called the heartwood.

Sapwood

The sapwood is the younger, softer outer portion of a tree that lies between the heartwood and the cambium (formative layer just under the bark) As comparatively new wood, sapwood is less durable and more permeable than heartwood.

While a floor purely of sapwood may be beautiful and smoother than heartwood, the softness and permeability of the sapwood makes it expand and contract easily, which can cause it to warp in certain conditions. This weakness also manifests differently in various tree species; some have sapwood that is strong and durable, others have weak, soft sapwood that is not appropriate for wood floors.

Many times, sapwood is graded higher than heartwood because it is smoother and less prone to knots and blemishes; the highest-grade sapwood is virtually free of any imperfections. Coloration of sapwood ranges from white to light and yellow blonde tones.

Heartwood

Heartwood is the older, harder central portion of a tree. It usually contains deposits of various materials that frequently give it a darker color than sapwood. Denser and more durable than sapwood, heartwood is found primarily in aged trees.

Heartwood is generally darker than sapwood, and doesn't have the same expansion and contraction problems that beset some sapwood. It makes a great wood floor because of its hardness and strength, and its resistance to many weather conditions. The hardness of heartwood, like sapwood, depends on the tree species and age of the tree.

Heartwood is usually graded lower than sapwood because it retains more imperfections and knottiness than sapwood. This is not necessarily a detriment in wood floors; many people like the natural, rustic look that a heartwood-dense floor achieves. And for numerous species, like the heart pine, heartwood is graded higher than sapwood. Coloration of heartwood varies from beautiful, deep reddish browns to yellows and ambers.

What this means for your hardwood floor

While many people choose either sapwood or heartwood, a very popular type of wood flooring comes from a mix of the two. Remember that the color differences between the two are less marked in some tree species, and more striking in others, like cherry, walnut, and hickory.

The mix may be graded (grading assigns the wood a value, and this affects the price - the higher the grade, the more expensive the wood) depending on different species' valuation of heartwood and sapwood and the amount of heartwood or sapwood in the wood. For example, different woods can be ordered and graded as no sapwood (sap-free), no heartwood (sap only) or mixed (heartwood and sapwood).

Staining and finishing a wood floor may be affected by the amounts of sapwood or heartwood in the floor because they accept and absorb stains and finishes differently. Also, heartwood is generally more stable than sapwood, so flooring with a high percentage of sapwood will shrink and swell more than flooring that is mostly heartwood.

Before deciding on a floor of heartwood, sapwood, or both, research different species of trees and their pros and cons, find out how a grade is assigned to the wood, and consult a knowledgeable wood floor installer. Armed with this information, you can buy the perfect floor safe and secure in the knowledge that it is exactly what you want.