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| Southern Pine Flooring: Storage & Acclimation |
Wood and Water Relationships
Wood is hygroscopic – it will absorb moisture and expand when exposed to
high humidity. Conversely, wood also expels moisture and shrinks in low humidity
environments, changing and balancing with its general surroundings. On
average, wood will change 1% in dimension for every 4% change in its ambient
moisture content. A door that periodically "sticks" is a good example of this
expansion and contraction behavior.
Before it can be used for interior purposes, a majority of the water in wood
must be removed. To achieve proper moisture content levels, Southern Pine
lumber is kiln dried prior to its manufacture into flooring. A kiln is a closed system
having temperature, humidity, and air flow controls that lower the wood’s
moisture content to desirable levels. Adjusting the heat, steam and air flow speed
during the kiln-drying process conditions the wood for its intended use, while
reducing defects such as splitting, warping, checking, and casehardening.
Moisture content is a measure of the weight of the water in wood, expressed
as a percentage of the oven-dry wood. According to the SPIB grading rules,
Southern Pine flooring must have a maximum moisture content of 15% for D
and Better grades in 1" and 1-1/4" nominal thicknesses (3/4" and 1" actual
thicknesses). However, if specified, represented, or grade marked as "kiln-dried"
flooring, the maximum moisture content shall be 12% for 90% of the pieces, and
15% moisture content for the remainder. Refer to Paragraph 162 of the SPIB
grading rules for more information.
Proper Storage and Handling
Moisture will damage flooring! Careful adherence to some reasonable,
time-tested practices during the distribution and delivery process from sawmill to
distributor, to dealer, to final installation site will prevent moisture problems and
visual damage to the flooring. Proper storage and
handling practices are paramount for assuring a
Southern Pine floor’s readiness and suitability for
installation.
An appropriate storage site at the distributor or
dealer would be a dry, enclosed building having a
level floor, with flooring stored in a clean location.
A wrapping of paper or plastic will further protect
the flooring from moisture and dirt. Using a first
in/first out (FIFO) inventory method will minimize
flooring storage time and reduce exposure to excess
dust and humidity. Flooring should always be delivered
to the jobsite under dry weather conditions!
Jobsite Acclimation
Assuming the flooring has been properly stored and transported, it is equally
important that the builder conduct a regimented construction timetable, completing
the tasks necessary to assure all of the following jobsite conditions exist prior
to flooring delivery.
The building’s interior must be thoroughly DRY. If the average moisture content
of drywall, subfloors, ceilings, and framing is below 12 to 14%, the building
components are considered to be dry.
Areas to receive wood flooring must have suitable ventilation.
| Required Jobsite Conditions: |
1 |
The building is fully enclosed; all windows and exterior doors are installed. |
2 |
The proper subfloor nailing base is installed. |
3 |
The heating/cooling system is operational. |
Proper jobsite acclimation is essential for the installation
of a high-quality, serviceable Southern Pine floor! |
If jobsite conditions 1, 2 and 3 have been met, sufficient preparation is
complete and the delivery of flooring may take place.
If any of the construction steps are incomplete prior to delivery, the floor
has a greater likelihood for installation-related problems due to excessive moisture
conditions.
Acclimating a Southern Pine floor allows time for the wood to adjust itself
dimensionally, enabling the floor to reach a balancing point — a state in which
it neither absorbs nor evaporates water vapor. This state is commonly referred to
as its equilibrium moisture content, or EMC. The acclimation time period is generally
between five to fourteen days for Southern Pine flooring, depending upon
humidity and/or jobsite conditions among rooms.
It is recommended that the material be sorted and stacked in each room
receiving flooring. Acclimating the material in this manner takes into consideration
varying ambient conditions that may exist between rooms.
Stack the flooring in unopened bundles, spacing it evenly and neatly.
Use clean, dry spacer sticks between each bundle level, allowing space
for air circulation between the bundles. Do not open the package banding,
but remove and dispose of any plastic or paper wrapping.
A wood moisture meter is a tool every installer of wood floors should
own. Guessing is virtually eliminated from flooring acclimation when
using a moisture meter.
After five days of acclimation, moisture meter readings should be
taken and recorded of the subfloor, the flooring and of the walls in each
room. Twenty-four hours later, take another reading. If the readings
show any consistency, the flooring has reached its equilibrium moisture content
and is ready for installation. If the moisture content readings fluctuate either up
or down, do not install the floor, as more acclimation time will be required. Wait
at least another day and take additional sets of readings. Until the Southern Pine
flooring, the subfloor nailing base, and the walls are neither gaining nor losing
moisture, acclimation is incomplete.
When the equilibrium moisture content is attained, the Southern Pine flooring
has been properly acclimated. It is now ready for installation.
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