Acclimation is an issue you ignore to your detriment when installing new hardwood floors. Wood is a hygroscopic material, which means it changes dimensions with different moisture conditions, and failure to acclimate your flooring can lead to cupping or gapping. You should acclimate solid hardwood and engineered and laminate floorboards, but acclimating solid wood is especially important. The boards need enough time to come into equilibrium with the room temperature and humidity conditions.
When you acclimate your hardwood flooring, you're allowing it to come into equilibrium with the room conditions before you install it. Ideally, its equilibrium moisture content -- which you can measure with a moisture meter -- should be between 6 percent and 9 percent, depending on the type of wood and the room temperature and humidity. To achieve this, the wood must remain in a controlled environment throughout the acclimation period -- ideally, it should remain in the space in which it is to be installed under environmental conditions that are typical for that space. Hardwood flooring performs best when the relative humidity is between 30 percent and 50 percent and the temperature is between 60 and 80 degrees Fahrenheit.
The period of time a particular flooring material should be acclimated depends on environmental factors as well as characteristics of the wood itself. Some exotic hardwoods take longer to acclimate, and they take longer to achieve equilibrium in a dry room than in a humid one. The National Wood Flooring Association recommends a minimum acclimation period of three days, and some flooring professionals recommend five to seven days. The most important factor isn't the amount of time the wood acclimates, though, but its moisture content. You should monitor moisture and refrain from installing the wood until the moisture content falls within the acceptable range of 6 percent to 9 percent.
To ensure the most stable moisture conditions for your wood flooring:
- Have it delivered on a dry day, and transport it to a closed room -- preferably the installation room.
- Open the containers and remove the plastic wrapping.
- Stack the flooring on shims that raise it at least 4 inches above the subfloor and allow air to circulate; never lay the floor boards directly on concrete.
- Keep the room conditions constant and avoid any activity that puts moisture into the air, such a painting or drywall taping. * Check the moisture after the minimum acclimation period, and allow the wood to stand if the moisture has not fallen into the equilibrium range.
Laminate and engineered floorboards aren't as vulnerable to moisture as solid wood -- they are constructed in layers, giving them more dimensional stability. Nevertheless, they still need to be acclimated -- the acclimation period is usually three to five days, which is typically specified on the container or on the manufacturer's website. It's also important to monitor subfloor moisture before installing any type of wood flooring, especially if the subfloor is concrete. Unusually high moisture may call for remedial procedures, such as covering the subfloor or the ground in a crawl space with a reinforced vapor barrier or providing extra ventilation in the crawl space.