Why do we need to acclimate our wood floor?
Dec 10, 2019 by SHAUN BEZUIDENHOUT
Most solid wood flooring products are manufactured to moisture contents between 6 percent and 9 percent, to closely match the interior equilibrium moisture content (EMC) of most homes in temperate regions (with HVAC operable), year round. When properly manufactured solid wood flooring is exposed to interior EMCs in the 6 percent to 9 percent range, acclimation is a short and simple process.
However, when a customer stores wood in an uncontrolled environment (such as an unconditioned warehouse, basement, pole building, or garage) for a length of time before the installation, the acclimation process becomes more challenging. These uncontrolled environments typically cause the wood flooring to take up moisture and increase in dimension (the change in product width is the biggest concern). This is the scenario for which you, the installer, must be wary. If you are going to install wood that has been stored in a cool or damp environment, please be sure to take the extra time and care required to acclimate properly.
Manufacturers typically provide written instructions on how to acclimate their products for the best performance. The bottom line is, wood is wood, and most of those instructions say the same thing. When the manufacturer doesn’t provide instruction on acclimation of their product always defer to NWFA Guidelines.
NWFA Installation Guidelines require that the average wood subfloor MC is no more than 4 percent from the average MC of strip flooring, or 2 percent for plank flooring, at the time of installation. The moisture content of the wood flooring and the subfloor (if wood based) is typically determined by a handheld resistance-type meter (prong meter) or capacitance-type meter (pin-less meter). It is hopeful that you have at least one type, or both types, of these meters at your disposal. If these steps are followed, a successful installation should result.
In the situation where the wood flooring is especially high in MC, extra time may need to be added to the acclimation period. Keep in mind, changing the MC in the wood will also change the shape of the wood. This will affect the installation process and must be taken into account during scheduling. To help expedite the process, there are several things that you can do to help reduce the MC of the flooring. It is highly recommended that all of the material be removed from the boxes (or other packaging) and placed on stickers. Stickers can be anything from scrap pieces of flooring to thick strips of cardboard. The goal is to create 1/2”-plus gaps between the boards as they are acclimating. Typically, these stickers are laid out on the subfloor perpendicular to the length of the flooring at 24” intervals to provide adequate support.
Once properly oriented to your available floor space, stack the first layer of flooring across the stickers. Lay the second layer of stickers on top of the first layer of flooring and repeat this pattern. Take caution not to stack too many layers of flooring, as the weight may leave an indent on the bottom layers depending on the hardness of your stickers and the hardness of the flooring you are acclimating (obviously less dense woods like walnut and cherry will indent easier than an oak or hickory). Be sure to align the stickers vertically as you stack your layers of flooring. Alignment of stickers will evenly support the flooring during acclimation. Also, the more time you have to condition, the closer the wood MC will be to both the environment and the subfloor on which it will be installed.
There are other effective methods of acclimation as well, but the key is to ensure that the wood has ample exposure time to the environment. The acclimation process is often overlooked or not done properly – typically due to time constraints on the jobsite. By following the simple steps outlined in this article, you can greatly reduce the concern of a customer coming back to you shortly after installation complaining about a gapped, cupped, or noisy installation.
Picture below: A recently installed, Hallmark True Collection - Onyx Oak