The Science of Wood: Understanding Hardwood Properties and How They Affect Refinishing

The Science of Wood: Understanding Hardwood Properties and How They Affect Refinishing

Hardwood floors bring a timeless elegance to any space, but understanding the science behind the wood is crucial for proper maintenance and refinishing. Different species of wood have unique properties that affect how they should be treated, especially when it comes to refinishing. This comprehensive article will delve into the science of wood, exploring the properties of hardwood and how these characteristics influence the refinishing process.

Understanding Hardwood

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Hardwoods come from deciduous trees, which are known for their dense and complex structure. This density makes hardwood an ideal choice for flooring due to its durability and resistance to wear. However, not all hardwoods are created equal. Each species has a distinctive grain pattern, hardness, color, and response to humidity changes, all of which play a significant role in refinishing.

Hardness and Janka Scale

The hardness of a hardwood is measured using the Janka hardness test. This test measures the force required to embed a 0.444-inch steel ball to half its diameter into the wood. Woods with higher Janka ratings are more durable and resistant to scratches and dents. For instance, Hickory has a high Janka rating and is known for its exceptional hardness, while Black Walnut has a lower rating, making it softer and more prone to dents.

Grain Patterns and Texture

The grain pattern in wood is determined by the way the wood is cut and the tree’s growth rings. Woods can have straight, spiral, or interlocked grains, each contributing to the wood’s aesthetic and its behavior during refinishing. Straight grains are usually easier to work with, while woods with more complex grain patterns may require special attention during the sanding and staining process to ensure an even finish.

Color and Aging

Hardwood floors can vary significantly in color, from light woods like Maple to dark woods like Ebony. Additionally, wood color can change over time due to exposure to light and air, a process known as patina. Understanding this natural aging process is important when refinishing, especially when trying to match new planks with older ones.

Moisture Content and Acclimation

Wood is hygroscopic, meaning it absorbs and releases moisture depending on the environment. This can lead to expansion and contraction, which can affect the refinishing process. It’s crucial to ensure the wood is acclimated to the room’s humidity level before installation and refinishing. The ideal moisture content for hardwood flooring usually ranges between 6% and 9%.

Preparing for Refinishing

Refinishing hardwood floors involves several steps, each influenced by the wood’s properties.

Assessing the Floor

Before starting the refinishing process, it’s important to assess the current condition of the floor. Look for signs of wear, deep scratches, or warping. The type of wood can influence how these issues are addressed. Softer woods may require more delicate sanding, while harder woods can withstand more aggressive techniques.


Sanding removes the old finish and prepares the wood for a new coat of stain or sealant. The hardness of the wood determines the grit of sandpaper needed. Softer woods require finer grits to avoid excessive removal of material, while harder woods can be sanded with coarser grits.


Staining can enhance the natural color of the wood or change its appearance entirely. The wood’s natural color and grain pattern will affect how it absorbs the stain. Test the stain on a small, inconspicuous area first to see how the wood reacts.


The final step is applying a finish, which protects the wood and can enhance its natural beauty. The choice of finish—oil-based, water-based, polyurethane, or others—can depend on the wood type. Some finishes may react differently with certain woods, so it’s important to choose a compatible product.

Challenges in Refinishing Hardwood

Dealing with Older and Historic Floors

Refinishing older or historic hardwood floors requires special consideration. These floors may have unique characteristics and may be more susceptible to damage. Preservation of the wood’s character is often a priority.

Addressing Gaps and Warping

Changes in humidity can cause hardwood floors to expand and contract, leading to gaps or warping. Addressing these issues requires understanding the wood’s response to moisture and employing appropriate techniques to minimize future movement.

Matching New Wood with Old

When adding new wood to an existing floor or repairing damaged areas, color matching can be challenging, especially considering the wood’s aging process. Custom staining and careful selection of wood species can help achieve a seamless match.

Understanding the science of wood is fundamental to successfully refinishing hardwood floors. Each species of hardwood presents unique challenges and opportunities in the refinishing process, from preparation to the final coat of finish. By appreciating the distinct properties of different hardwoods, homeowners and professionals alike can ensure that their floors are not only beautiful but also durable and well-preserved for years to come.