Hardness One of the most important measures of strength, durability and resistance to wear is "side hardness" - commonly referred to in the industry as Janka hardness. Janka measures the load required to press a 0.444-inch diameter steel ball into the wood to one-half its diameter. The Janka measurement is usually based on an average of plainsawn and quartersawn wood, as each provides different results.
Moisture content & dimensional stability Moisture content plays a significant role in how wood behaves during manufacturing and installation. Wood, being a live cell structure, is most stable at fiber saturation of 30 percent or more - a level not suitable for wood flooring. Below 30 percent moisture content, wood changes dimension when it gains or loses moisture. Bringing the moisture level down by a combination of air drying and kiln drying brings the moisture content to a range of six percent to nine percent, which is optimal for solid wood flooring. The installation environment's moisture content can range from lows of three percent to highs of 18 percent, depending on the species being used, the geographic location and the time of year.
All solid wood flooring should be acclimated to the environment for a period of time best determined by the qualified installer or the guidelines set out by the National Wood Flooring Association which calls for up to 2 weeks. To properly acclimate, the wood should be separated and securely stacked with separators or "sticks" between the layers. This assures proper air flow. The environment should be completed - including painting and plastering as they introduce moisture. Wood flooring professionals need to inform end-users about the behavior of solid wood flooring in relation to moisture. Most solid wood floors will contract during periods of low humidity and expand during warmer humid months. End-users can minimize the effect by stabilizing the environment through temperature and humidity control. Most important of all is to start the installation in an environment that has been properly prepared.
