|Hardwood is a living substance which reacts
to changes in relative humidity. Wood gains and loses moisture
before and after installation, as surrounding conditions fluctuate.
Indeed, wood expands in the summer when humidity level is high
and contracts in the winter when the humidity level is much
lower. To minimize the expansion or contraction of your hardwood
floor, it is recommended that the building should be well ventilated
and the relative humidity level maintained at 45 % all year
long. Before you begin, plastering and cement work must be completely
dry. It is strongly recommended that the
wood be left to acclimatize at house temperature for a period
of at least 24 hours at the ideal relative humidity level which
is 45 %.
Test concrete slabs for excess moisture Rubber Mat Method
(Useful Only On Light-Colored Concrete) - Lay a flat, non-corrugated
rubber mat on the slab. Place a weight on top to prevent moisture
from escaping and allow the mat to remain 24 hours; if the
covered area shows dark, wet marks, too much moisture is present.
Polyethylene film method - Tape a 12" (30 cm) square
of clear polyethylene film to the slab with plastic moisture-resistant
tape, sealing all four edges. If no condensation collects
under the film after 24 hours, the slab is dry enough for
Make tests in several areas of each room. When test indicates
excess moisture, wait for the slab to dry naturally or accelerate
drying with heat and ventilation, then test again before installing
Installation methods on slabPlywood-on-slab - Begin by covering
the slab with a vapor retarder of either asphalt felt, building
paper or polyethylene.
Asphalt felt or building paper - First, prime the slab and
apply cold, cut-back asphalt mastic with a notched trowel
at the rate of 50 sq.ft. per gallon (1m2 per liter). Allow
to set for two hours. Unroll 15 lb (6.8 kg) asphalt felt or
building paper, lapping the edges 4" (10 cm) and butting
the ends. Over this, apply a second similar coating of mastic
and roll out a second layer of asphalt felt or paper in the
same direction as the first, staggering the overlaps to achieve
an even thickness.
Polyethylene - When the slab is well above grade and the
expected annual rainfall is light to moderate, cover the entire
slab with 4-6 mil polyethylene film, overlapping the edges
4-6" (10 to 15 cm), and allowing enough film to extend
under the baseboard on all sides.
When moisture conditions are more severe, prime the slab
and apply cold, cut-back mastic with a straightedge or fine-tooth
trowel (100 sq.ft. per gallon) (2 m2 per liter). Allow to
dry for at least 90 minutes. Unroll 4-6 mil polyethylene film
over the slab, overlapping the edges 4-6" (10-15 cm).
In either cases, roll the film flat or "walk" it
in, stepping on every square centimeter to insure proper adhesion.
Puncture bubbles to release trapped air.
Install the plywood after the vapor barrier is in place.
Loosely lay a nailing surface of 3/4" x 4" x 8"
(19 mm x 1.22 m x 2.44 m) exterior plywood panels over the
entire area, leaving a 3/4" (19 mm) space at the wall
line and 1/4"-1/2" (6-12 mm) between panels. Cut
plywood to fit within 1/8" (3 mm) near door jambs and
other obstructions where finish trim will not be used. Lay
plywood diagonally across the direction of the finished floor
to help prevent cracks along panel edges.
Fasten plywood to the slab with power-actuated fasteners,
securing the center of the panel first, the edges, using nine
or more nails.