Acclimation: Environmental Conditions Before, During, and After the Installation

Many factors can play into the performance of a hardwood floor. None is more important than how moisture can affect flooring. Hardwood flooring professionals know that wood is a natural material that can absorb and release moisture depending on environmental conditions. These conditions should be checked before the wood is delivered to the jobsite.

If you have ever been to an NWFA installation course, you have heard a decent amount of information and conversation regarding moisture and wood. How to test and document moisture on the jobsite and, depending on conditions, when to install or not to install the flooring. The NWFA has a separate publication covering just this topic, “Moisture and Wood,” which can be an additional resource if you want to understand more about how moisture
affects wood flooring.

To start the acclimation process correctly, it is best to ensure you control the environmental conditions at the jobsite. As mentioned previously, this starts before the flooring is delivered to the jobsite. For instance, your builder calls you and states that the job is ready for installation of the wood flooring.

In their mind, the schedule is ready for the installation. A jobsite evaluation should be done to check for any issues. While you already may have a list of things you check during a pre-delivery jobsite evaluation, here are a few items to make sure you are verifying before the delivery of flooring:

1. Is the jobsite completed to the required stage of construction?

  • All roofing, flashing, and gutters are complete
  • All windows and doors are installed
  • HVAC is up and running and set to maintain the parameters of the flooring manufacturer or NWFA installation guidelines
  • Crawl space (if applicable) is encapsulated properly with no moisture present

2. Has the exterior grading been done to allow moisture to shed away from the building?

  • While final landscaping may not be completely necessary, a completed rough grade will help minimize water pooling against the building’s foundation and finding its way into the jobsite.

3. Has all the “wet work” been completed?

  • All drywall and major painting is complete
  • The tile contractor has completed all installation and grouting

4. After the previous items have been checked, measure and document the moisture content of the subfloor or the concrete substrate in addition to taking the temperature/humidity of the jobsite. If your readings are too high, your flooring will absorb that moisture.

  • The moisture content of a wood subfloor should be within 2-4 percent of the expected wood equilibrium moisture content or EMC of the flooring (depending on width).
  • If you are gluing the flooring to a concrete substrate, ensure all moisture testing is complete and within the parameters of the adhesive system being used.

Regarding Moisture – Get the jobsite ready for the wood; then get the wood ready for the jobsite.

Here is a common phrase used in many installation courses regarding moisture…
“Get the jobsite ready for wood; then get the wood ready for the jobsite.”

This means doing the previously stated checks and balances before scheduling the wood delivery. If the jobsite is not ready, your flooring will acclimate to these conditions and not the living conditions to which the flooring will be exposed once the owner takes possession.
This will cause an awkward conversation a few months down the road when that flooring does officially acclimate in place, possibly causing cracking/popping, cupping, unsightly
gapping, and/or irreparable damage.

For additional information about acclimation, check out the NWFA’s Moisture & Wood publication at

So now you have taken the time to check the jobsite conditions of your upcoming job before having the wood delivered. All exterior doors and windows have been installed, and all “wet work” has been completed. HVAC is up and running, and the subfloor readings are within NWFA installation guidelines. Now you can have the flooring delivered and start installing the flooring, correct?

Well, this is now when the official acclimation of the flooring material can start. The acclimation processes may vary depending on whether you install prefinished or unfinished material. It also can vary depending on if it is solid or engineered. Check the installation guidelines of the material you are using to acclimate the flooring properly. Ensure the building owner maintains the living conditions during this acclimation process. Take moisture readings using a moisture meter throughout the process. Document these numbers and the temperature and RH readings using a thermo-hygrometer. In any situation, there should be no more than a 4 percent difference between a wooden subfloor and the flooring. If the flooring is to be glued over a concrete slab, consult your adhesive manufacturer for testing recommendations and guidelines.

If you are not familiar with the acclimation process, dimensional stability, and change coefficient of each wood species or figuring out the equilibrium moisture content (EMC) of your area, as I mentioned earlier, the NWFA’s “Moisture and Wood” publication goes into great depth regarding these and many more items regarding moisture and wood. The moisture content graph shown on this page commonly is used while explaining the effects of moisture in the wood.

This graph tells us that if we keep the temperature at 70 degrees and 40 percent RH, the EMC of that flooring, if kept in that environment, eventually will be around 7.7 percent. If you are trying to install a floor that is going to be kept in these conditions, you will want to make sure you are getting multiple readings throughout the flooring to measure an overall average percentage of the flooring as possible before starting your installation.

You have completed the job and are about to be paid. This is the time that could be the most critical part of long-term floor care: advising your customer on how to best maintain their new floor after the installation.

As you see in the shaded area in the graph, the NWFA recommends maintaining the environment at 60° to 80° and 30 percent to 50 percent relative humidity. If the floor manufacturer provides care and maintenance guidelines, ensure the floor owner receives a copy of that document. If one is unavailable or you do not have your own version, at least leave behind something that tells them how to maintain their new flooring correctly. If it was a sand-on-site project, most finish manufacturers have a care and maintenance guide you could provide. Just make sure it contains the verbiage to maintain the proper environmental conditions.

Understanding the relationship between moisture and wood allows us to understand better what to expect as we work with the flooring products and how they will perform in the environment we are planning on installing them. It is undisputed that moisture (or lack of moisture), whether in the form of liquid, vapor, or bound water, will affect the performance of wood flooring, regardless of style, species, width, installation method, or construction. As professionals in this industry, we are responsible for mitigating the adverse effects of moisture on wood floors and communicating to our customers how to maintain them properly.

Matt Thrane is a training specialist and handles new business development for
Gehl Flooring Supply Inc. in Wauwatosa, Wisconsin. He can be reached at

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