General Flooring Knowledge, Hardwood Flooring, Installation

Acclimatizing Hardwood – A Primer

“How long should I acclimatize my new hardwood flooring before I install it?”

At, we get asked this question.

All. The. Time.

The answer is, it depends. There are a couple moving parts that are inter-related that will determine the proper procedure for acclimatizing hardwood.

Since wood flooring projects are a major investment, it is wise to understand the true meaning of acclimatization. Improper acclimatization of your wood floor can lead to installation issues, such as buckling or gapping, things that the manufacturers’ warranty will definitely not cover.

Even though most manufacturers give a guideline to acclimatize their solid or engineered wood floor, proper acclimatization should be about more than just the amount of time that you let flooring sit on the job-site. There are two important related factors to consider in order to have a successful installation. First, the wood floor moisture content (MC) and second, the relative humidity (RH) in the surrounding environment.

Kiln Drying

In a perfect world, hardwood flooring should be dried specifically for the climate in which it will be installed. Since this task is unfeasible for most mills (because of logistics and efficiency limitations) industry standards suggest 6% to 9% as a desirable MC range for wood floors fresh out of the mill. In other words, it is a fairly safe MC range for hardwood flooring to perform in both drier and more humid regions.

According to the National Wood Flooring Association, “Wood flooring … is subject to dimensional change as a result of variations in moisture, temperature and humidity. Wood flooring simply needs to reach moisture content level in equilibrium with the surrounding environment in which it will be installed. Warranty coverage generally requires that conditions be maintained between 30% to 50% relative humidity … for the life of the floor.”

So, now that we know what the proper range of both MC and RH are, let’s examine some specific real-world situations. Things are not always as perfect as we hope on many job sites, especially for new construction. Certain conditions should be met before wood flooring is delivered to the job site.

Scenario 1

The builder wants to meet the deadline for an open house at the end of the month. A batch of wood floor is delivered to the home with proper 6 to 9 % MC. Inside the house, drywall taping, mudding and painting is still going on. The manufacturer recommends a minimum of 1 week acclimatization period prior to installation. One week later, the installer shows up to install the hardwood. Twenty-four hours before the open house for potential home buyers, the builder notices large gaps in his hardwood floors.

The Reason

The builder was acclimatizing the floor in the environment in which the RH was much higher than normal living conditions. Therefore, instead of conditioning the wood floor to the right environment, he was adding moisture to the wood flooring. This is a problem because the wood will expand due to taking on more moisture, and when the flooring eventually adjusts to normal (ie, lower RH) living conditions, it will shrink, resulting in gapping or surface cracks.

Scenario 2

Next, let us examine what happens when we install a high moisture wood floor into a house with ideal relative humidity of 40%. This time you receive a batch of hardwood floor with 11-13% MC for your house remodeling project. You were told to acclimatize the wood for a week before installation by the sales person at the retail store. The floor contractor installs your floor according to manufacturer’s guideline. Several months later, right in the middle of the winter, you start to notice gaps which can fit a loonie between the planks in your hardwood.

The Reason

The one week was not enough to acclimatize the hardwood floor from 11-13% MC to 6-9% MC you need in your Ontario home. In the winter heating months, your floor will give out moisture – the planks shrink and gaps form. If the same floor was delivered into a house in Florida, where winters are more humid than in Ontario, the outcome might be quite different, because the equilibrium moisture content will be between 11-13% MC.

Contrary to popular belief, wood floor acclimatization has less to do with the amount of time, and more to do with its MC being in equilibrium with the environment in which the floor is installed. Knowing the common pitfalls and how to avoid them will save you from headache, and heartache, down the road.

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