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There is a common misconception among contractors that if you bring wood flooring into the workplace and let it sit for a few days, it will acclimate properly and be ready to install. This is a big mistake that costs flooring contractors time and money.
According to the National Wood Flooring Association (NWFA), wood floor acclimation is “the process of adjusting (conditioning) the moisture content of wood flooring to the environment in which it is expected to perform”.
Contrary to belief, it has less do with the amount of time you should let flooring sit to acclimate on the job site and more to do with monitoring the moisture content of various components.
It is a fact that wood flooring will always perform best when the environment is controlled and remains within a relative humidity range of 30-50%. The temperature should also be controlled within a range of 60-80 degrees Fahrenheit.
Wood flooring installation should always be the last job of any construction project.
Certain conditions should be met before wood flooring is delivered to the job site.
Make sure the job site is ready for the wood, and the wood is ready for the job site. Wet elements including plaster and paint should be completed and dry before the wood is delivered to the job site.
We asked Levon Karapetyan from Northern California’s prestigious Artex Flooring Inc. how he prepared a job site for delivery of wood flooring…he said, “Before we receive a shipment of wood flooring, we monitor the job site to make sure the relative humidity is in compliance with recommended standards, which is 35-60%. We also make sure the doors, windows, and HVAC are installed and functioning. We check the perimeter of the house for any suspicious areas that need to be brought to the contractor’s attention.”
Communication at this point between the flooring contractor and the general contractor is essential. Don’t buckle under pressure from the contractor or homeowner if the above conditions have not been met. They may say, “Don’t worry about it…just put the floor in now…we’re running behind schedule.”
They may not care now, but they will care six months or one year down the road when they have flooring problems…and those problems will be your problems to fix.
Levon believes it’s important to educate your clients with useful information.
“It’s always good practice to keep your clients informed, even though they are very educated. You need to give them as much information as possible to ensure the success of their wood flooring.”
We asked Levon how he deals with builders or clients insisting flooring gets installed when conditions aren’t suitable, and he said, “If the moisture content is high on the concrete or on the job site, we tell the contractor we have to follow certain steps to bring relative moisture and humidity down with dehumidification or HVAC. Then we’ll come back and check again to make sure the moisture content is in regulation according to suitable moisture content standards. If it is, we will then bring in the wood flooring.”
When asked if he runs into humidity problems with new construction settings he explained, “We always make sure the wet trades are completed before we bring the flooring in. We won’t deliver the material while they are still working. After we have taken all precautions and know the job site is ready, we will bring the wood flooring in and let it sit for one to two weeks depending on the situation, and then we will proceed with our installation.”
As Levon mentioned, it’s always better to delay bringing in wood flooring materials if the walls were just painted or the subfloor isn’t completely dry. Wood flooring is hygroscopic, meaning it will naturally absorb moisture and change dimension. Wood will expand when it retains moisture and become smaller when it loses moisture. This definition is defined by the NWFA along with other useful resources.
If acclimated wood flooring is delivered to a job site while the contractors are still painting, the wood flooring will absorb the moisture of the paint, increasing the moisture content of the wood.
Solid strip wood flooring (less than 76 mm wide) that has been acclimated properly will not have more than a 4% moisture content difference between the flooring and the subfloor. For wider flooring (more than 76 mm wide) there should never be more than a 2% moisture content difference. Wider boards tend to have more movement issues than narrow boards.
Conditions of our example below may vary because of your geographical location and the species of wood flooring you are using:
If the subfloor moisture measurement comes in at 7-10% (measuring with a properly calibrated wood moisture meter) and your hardwood measures in at 7-10%, it’s usually safe to assume the job site is ready for the wood and the wood is ready for the job site.
If the job site is normalized to an in-use reading for your region and the subfloor and the wood flooring moisture (wood flooring less than 76 mm wide) is within 4 points of each other, the flooring is acclimated and ready for installation.
The following conditions should always be established before wood flooring is delivered:
Once the job site is ready and the wood flooring has been delivered, the time it will take to acclimate wood flooring will depend on:
Imported species or tropical species typically require more time to acclimate because of higher density and oil and resin content.
It is highly recommended that you measure the moisture content of wood immediately after delivery to establish a baseline.
The most efficient way you can record accurate wood moisture content and representation is to check and measure the moisture content of 40 boards for every 1,000 square feet.
Levon agreed with this statement saying, “We check up to 40 boxes and take moisture readings on different bundles.”
When we asked Levon if there was anything else he did to help acclimate product prior to installation he said, “The HVAC should be turned on five days before installation and left running after the job is complete. The main thing we need to accomplish is to keep the environment as close to the living environment as we can. That’s very important when it comes to a successful installation.”
As the NWFA suggests, “Calculate what the optimal wood flooring moisture content is (baseline) by dividing the high season and the low season. Example: If your region has an expected EMC from a low of 6% to a high of 9%, the baseline moisture content of the wood would be 7.5%.
Wagner Meters is the most respected moisture meter company in the world, providing flooring professionals with quality handheld devices that help establish a baseline and gather additional moisture measurements you can record and keep an eye on.
These meters are the most valuable instruments used in the acclimation process. They measure the moisture content of the subfloor, concrete and the moisture content of the wood flooring to be installed. These measurements will provide you with precise and accurate conditions that will help eliminate flooring failure if conditions are not suitable.
Moisture measurements will also help you decide if the subfloor or concrete at the job site are dry enough to receive wood flooring. If the subfloor is too wet, moisture will be absorbed into wood flooring materials and flooring will expand and buckle.
If flooring materials retain moisture at the time of installation, the flooring will shrink when equilibrium (EMC) has been reached, which will cause wide gaps and spaces in the flooring.
These moisture content measurements are crucial if you have a problem with faulty flooring received from the manufacturer. The warranty of many manufacturers will be void if you can’t back up your work with solid evidence.
Levon highly recommends moisture meters to flooring professionals: “My moisture meter is always with me. If I ever have a situation, it’s there…I always have it handy. If you’re a wood flooring professional, you should always have a moisture meter with you.”
Acclimation of wood flooring begins with proper storage at the job site.
Wood floor acclimation can be achieved by cross-stacking and spacing wood floor materials to encourage air circulation around the boards. Most manufacturers recommend materials acclimate for a minimum of three days with no maximum suggested.
In order to make a proper judgment call on how much time is needed to acclimate your wood flooring, you need to have a baseline and know what the moisture content of wood flooring is when it is delivered.
Levon shared his on-site storage methods with us: “If the flooring is an unfinished material, we cross-stack the wood. If it’s a finished material, we read the instructions and follow the manufacturer’s recommendations. It doesn’t matter if it’s engineered or pre-finished. If there is a high content of moisture, it can still cause big problems.”
It’s important that wood floor materials reach a moisture content that is in equilibrium with expected use. In order to accomplish this, it will take as long as it takes. Regular moisture readings will indicate when wood flooring has stabilized and it is in equilibrium (EMC) with its environment. At that point, no further changes will occur.
Even with engineered flooring, it is suggested by some manufacturers that in order to retain coverage with the warranty, the job site has to be maintained between 30-50% relative humidity, and these conditions must also be maintained after installation.
When asked if Levon acclimates engineered flooring, he said, “We don’t skip a step just because the flooring is engineered flooring. We always check the moisture of the wood panels and the concrete. We take moisture content and relative humidity very seriously because those are two areas that can cause flooring failure.”
Floors perform well when you invest time during the installation process to ensure moisture, temperature and humidity are controlled and stabilized.
Failure to properly initiate wood floor acclimation before installation begins may compromise the integrity of your floor. Excessive gaps, warping or cupping can occur after the installation is complete; the expansion joint may also be compromised, which will result in further damage.
Failure to acclimate the flooring will also void the manufacturer’s warranty if such problems arise.
When you take the time to prepare your job site location, bring it in at the right time, determine the expected seasonal change for your location, and make sure everything is acclimated correctly, you’ll never have a problem with hardwood flooring.
Larry Loffer is a senior technician at Wagner Meters, where he has over 30 years of experience in wood moisture measurement. With a degree in Computer Systems, Larry is involved in both hardware and software development of wood moisture measurement solutions.