Wood Block Acclimation
Understanding Acclimation for Wood Block Flooring
The purpose for acclimating wood blocks prior to installation is to allow the moisture content of the blocks to adjust to “normal” conditions, the ambient temperature and humidity that will prevail once the facility is opened. This requires the permanent heating, ventilating, and air conditioning (HVAC) system running and balanced.
Before the wood blocks are delivered the jobsite must be checked to determine if it is ready. The structure should be fully enclosed, with doors and windows in place, and the interior climate controls operational for at least 48 hours prior, to stabilize the moisture conditions of the interior. Wood flooring should not be delivered until all wet work is completed and dried.
For individual blocks: Acclimation must include de-palletization or removal of the blocks from cartons or pallets, spreading them in piles. (The lower and more spread out the pile the faster the acclimation).
For strip blocks: Strips must be open stacked for exposure to both top and bottom.
For blocks on panels: Remove panels from cartons to allow exposure.
For blocks on engineered planks: Open packages to allow exposure.
If conditions are not “normal”, acclimation may be harmful. For example, if the humidity were too low, acclimating could cause the moisture content of the blocks to become too low. In so doing, you might then be installing the block too dry during the dry heating season, and expansion problems may develop during the more humid months.
Therefore, you must know the EMC or Equilibrium Moisture Content of wood in your region. You also need to know the moisture content of the wood block on arrival. These readings will guide you in the length of acclimation. The blocks brought to a jobsite might already be at the proper moisture content (EMC), and therefore acclimation for any length of time may not be needed. The length of acclimation should be determined by the installer who understands the dynamics of water and wood. Knowing and recording the moisture content of the blocks at time of delivery, and knowing the expected moisture content is essential.
At equilibrium moisture content, the blocks will neither gain nor loose moisture because they have reached equilibrium with the vapor pressure of the surrounding atmosphere. Changes in humidity and temperature will cause a change in the EMC. Although protective coatings slow the changes in moisture content, the blocks will ultimately reach a new equilibrium.
NOTE: We always recommend at least 2 days acclimation prior to installation. We never deliver and install blocks on the same day. Please call us with any questions.
Humidity maintained above 60-70% at normal residential and commercial temperatures can adversely affect wood components. Humidity sustained at or above this level can result in an equilibrium moisture content of 12% or higher, with associated expansion (Wood Handbook U.S. Department of Agriculture, Forest Products Laboratory) Humidity maintained at or below 25% to 30% can adversely affect wood components, and result in an equilibrium moisture content below 6%. This condition would cause greater than normal shrinkage, with associated cracks.
For the best performing wood flooring installation, acclimate and install at the average of the highest and lowest anticipated level of humidity. If the range were 35-50%, acclimation to 42% would be ideal.
Shrinkage Cracks in Wood Block Flooring
There is no official standard for determining contraction tolerance for wood block installations. We, at Kaswell Flooring Systems, have established a standard of 3% as an amount of contraction that could be expected for many species of end grain, and should be considered normal. To determine percentage of shrinkage, measure all voids, add them, and take the sum as a percentage of the flooring ten feet in two directions. If properly acclimated and installed, and if environmental conditions are properly maintained, shrinkage after installation can provide a natural and effective space to accommodate future expansion. After re-filling and re-sealing in-place shrinkage will restore the flooring to a like new condition.