The point of acclimating wood flooring before
installing it is to allow the moisture content of the wood to adjust to
"normal living conditions" at the site--that is, the temperature
and humidity conditions that will typically be experienced once the
structure is occupied.
Thus, it does no good at all - in fact, it is
likely harmful-to store wood flooring at the jobsite under conditions that
don't reflect those normal environmental conditions.
The wood flooring industry has done a good
job in recent years communicating the message that wood flooring is a
dynamic material subject to changes in dimension as a result of changes in
humidity in the surrounding environment. That has led to increasing
awareness of the need to acclimate wood flooring before installation.
Unfortunately, some installers have heard the message as, "Leaving wood
flooring at the jobsite for two weeks will properly acclimate the wood, no
matter what the conditions are."
In truth, some wood flooring may already be
at the proper moisture content when it's delivered. To allow it to sit at
the jobsite under excessively humid conditions will only cause the flooring
to absorb unwanted moisture.
So, the key message is not that acclimation
is good, and that's all you need to know. Rather, installers need to
understand the dynamics of water and wood and make educated judgments about
when and how much acclimation is required. To do so requires knowing what
the moisture content of the flooring is at the time of delivery and what its
expected moisture content will be "in use."
Wood at the warehouse
~ Once milled, the flooring should be stored in dry, well-ventilated
warehouses before shipment to jobsites. These are some recommended
guidelines for handling and storing hardwood flooring:
A covered area can also provide protection,
although this is not a guarantee in a damp season or environment. If this is
not possible, all top pallets should be covered with polyethylene film or
other water-proof covering.
- Unloading: Flooring should be unloaded in
good, dry weather, never in the rain.
- Warehousing: Flooring should be stored in
an enclosed, well-ventilated building and located in areas where similar
fine millwork is stored. The storage area within the building should be
clean and dry. The stacks of flooring should have good air circulation
and no water drainage nearby.
- Preventing condensation: When air in a
building is more humid than outside air, moisture may form on the
underside of the non-insulated roof and affect flooring. Insulation in
the roof or walls can prevent condensation.
The storage building should ideally have
controlled humidity. Continual dry heat may dry flooring below its desirable
moisture content, which could result in buckled floors if flooring is
installed without proper acclimation. Conversely, storage in a damp area can
introduce unwanted moisture and expansion in the flooring, which could
result in unacceptable cracks between boards if flooring is installed
without proper acclimation.
Wood at the jobsite ~
Before wood is delivered, the jobsite must be checked to determine if it is
ready. Wood should not be delivered if jobsite moisture conditions
excessive. Otherwise, one will absorb moisture from the other.
The structure should be fully enclosed, with
doors and windows in place, and interior climate controls should be
operating for at least 48 hours to stabilize the moisture conditions of the
interior. Once at the jobsite, the wood should be set indoors and spread
over the subfloor. About four days should pass before an installation is
started. Moisture contents of both the flooring and the subfloor must be
checked and recorded before any work begins.
If flooring is delivered on a damp day or
during rain, the boards will absorb moisture. If installed in this
condition, the flooring will shrink a few months later and show cracks.
Wood flooring should NOT be delivered to the
jobsite until plastering and painting are completed and dried. Moisture
evaporates from damp walls into the air within the house, and some of it
will be absorbed by the flooring.
Another condition that causes flooring to
pick up moisture during construction is less obvious, but more common: If
the heating or air conditioning is not operating from the time the floor is
installed until the house occupied, the humidity may be higher than it would
be if the house were occupied.
Only after getting satisfactory moisture
measurements from the concrete slab and the subfloor, and only after wood
has acclimatized to the jobsite, is the installer ready to install. When
installation is completed, good practice calls for a delay of one or more
weeks for further acclimation before beginning the sanding and finishing
part of the job.
Checklist" can assist as a pre-installation evaluation of the
jobsite. Problems identified while completing the checklist should be
brought to the attention of the general contractor or owner before
installation is begun.