If you’re looking to install new hardwood floors, you’ve probably come across technical specifications related to the hardness, density, and other characteristics of wood. These mechanical properties may make a lot of sense to the insiders of the hardwood industry, but to the average homeowner they might just as well be written in Latin. However, knowing what these measurements mean can help you better understand the type of hardwood flooring you’re interested in and whether it’s right for the room you want to install it in. Here are some key mechanical properties of hardwood, what they measure, and why they matter, all in plain language.
Hardness: Often called Janka hardness, this specification measures how resistant a species of wood is to indentation. The test consists of measuring the pounds of force required to embed a small ball (0.444 inches or 11.28 mm) into the wood a distance of half its diameter (0.222 inches or 5.64 mm). Janka hardness is measured in pounds, and the higher the number, the harder the wood. For example, exotic Ipe has a Janka hardness of 3,680 lbs., while domestic Douglas Fir has a hardness of only 950 lbs. Hardness is important if you are installing the wood in a high-traffic area or if the wood will support heavy furniture such as entertainment centers or pianos.
Modulus of Rupture (MOR): Also known simply as Strength, MOR refers to the measure of force required to break the wood. In other words, it is the load capacity of the wood. MOR is measured in pounds per square inch, or psi. The higher the psi, the stronger the soil. Like hardness, MOR is important to know if you plan to put heavy furniture on your new floors.
Module of Expansion (MOE): Also called Rigidity, MOE is a measure of the stiffness or flexural strength of wood. MOE is also measured in pounds per square inch and, due to the intense force required, is expressed in exponential terms. For example, the MOE of the Douglas Fire is 1,950,000 psi, expressed as 1,950 1000 psi. The MOE is an important indicator of whether your floors will sag. The higher the MOE, the less likely the wood is to stretch and buckle.
Density: The density of a hardwood is related to its weight and hardness, and should be considered in a similar way. Measured in KG per cubic meter (KG/m3), density tells you how much wood is in a cubic meter. The higher the density, the heavier and harder the wood. Higher density isn’t always better, especially if you’re installing flooring on a second or third story. Density is also a good indicator of the wood’s natural resistance to water and termites. The denser the wood, the more difficult it is for water and boring insects to enter.
tangential shrinkage: This property refers to how much a wood species tends to shrink during the drying process. It is expressed as a percentage and applies only to the width of the board or plank. The shrinkage factor is a good indicator of how much your hardwood floors are likely to warp or sag: the lower the percentage, the more stable the floors will be.
Radial shrinkage: Similar to tangential shrinkage, radial shrinkage tells you how much the wood species can shrink through the thickness of the board. It is also expressed as a percentage. A low percentage is good, but the most important thing is the combination of these two measures. The closer the two are, the more stable the wood is. For example, maple has a tangential shrinkage of 9.9% and a radial shrinkage of 4.8%. The differential is 5.1. Walnut, on the other hand, has a tangential shrinkage of 7.8% and a radial shrinkage of 5.5%. Although Walnut’s radial shrinkage is higher than Maple’s, Walnut’s differential is 2.3, much lower, and therefore less likely to warp or sag.
Many of these mechanical properties of hardwood can be confusing, and some industry experts even struggle with the concepts. However, knowing the basics of what they measure and why they are important will help you choose the perfect hardwood species for your flooring or decking needs.