With the introduction of engineered
flooring, hardwood floors can be used in virtually every room in the
house, even in basements. Water on or near the building site is still a
consideration, however. It cannot be ignored or neglected.
Moisture comes from a variety of
sources-from the earth itself, from surface water (i.e., rain water
runoff), as well as from the interior atmosphere. Let's consider the
various ways that moisture problems originate, and how they can be
controlled and prevented.
A room that is exposed to excessive
moisture would be prone to trouble if solid wood flooring were installed
in it. Basement floors are particularly tricky installations. But some
products, such as laminated flooring, may be suitable in many of these
circumstances because of their dimensional stability.
The use of these alternative materials is
necessary when the installation is below-grade. "Below grade"
is defined as any part of the slab having four inches or more of earth
above it. Additionally, walk-out basements are considered a below-grade
application, even if a portion of the basement is above ground.
Most laminated (also called engineered)
flooring consists of two or more layers of wood glued together, with the
grain of each running at 90 degree angles to the layers adjacent This
tends to result in increased dimensional stability.
Use of engineered wood flooring
Engineered wood flooring uses multiple
layers of wood glued together, with the grain of each running at
90-degree angles to the layers adjacent. As the wood fibers absorb
moisture and want to expand, each layer is restrained by the other and
improved dimensional stability results.
Because it displays far less expansion
and contraction with moisture changes, laminated flooring can be
successfully installed in areas with wide humidity variations. It
usually does not require full acclimation before installation. In
on-grade or above-grade installations, various flooring types can be
used: solid or laminated. Moisture is still a consideration, although it
is less likely to cause problems than in below-grade installations. Once
the grade limitations are determined, it's time to look at other
potential sources of moisture.
Potential sources of
During the building of a new home, moisture can enter the house in a
number of ways. When the frame is going up, the 2-by-4s and subfloor
materials often get rained on. Because builders usually work on tight,
demanding schedules, homes are sometimes built trapping moisture that
needs time to evaporate. The amount of moisture introduced by framing
lumber and the wet trades can be significant. See Moisture Detection Equipment
GROUND WATER: Sometimes the level of the water in the ground is
raised above the bottom surface of the foundation due to:
heavy or prolonged rains;
a spring that appears only during wet
seasons and is not discovered when the house was built;
water flowing along an impervious layer
within the soil.
Any of these may cause water
to penetrate the foundation walls or rise through the ground surface
into the foundation or crawl space.
Rain water falling on the ground or from the
roof can pass through or under the foundation walls. In some areas,
heavy soils may retain surface drainage and cause water pressure against
the foundation walls or slab.
Surface drainage problems
may also occur because the crawl space is below the finish grade outside
CRAWL SPACE: Many
houses are built over a crawl space--that is, the floor of the house is
built over an open space that is deep enough to allow a person to gain
access to the under floor area by crawling. The minimum depth of the
crawl space should be 24 inches under the floor joists or 18 inches
under the girder. An 18-inch clearance beneath any ductwork is also
desirable. Moisture problems within a house that show up as condensation
and/or frost on windows in the living area, can result from dampness in
the crawl space, or from inadequately vented living space. Moisture
problems in crawl spaces may be due to the construction of a crawl space
in an area of high water table, improper grading of the lot for drainage
or the omission of moisture control devices such as vapor barriers,
ground cover and ventilation openings.
Obvious symptoms of
excessive moisture passing upward through the floors may include any of
the following: a musty odor; mold on the walls near the floor, in
corners and in closets; moisture condensation on insulated windows or
storm windows; and moisture condensation in the walls with resulting
paint peeling. Some of the more common ways moisture gets into crawl
ground water moving through the
foundation walls or up through the earth floor;
surface water moving through the
foundation walls or flowing in through ventilators;
capillary rise of ground moisture;
"green" slabs, or concrete
foundations that weren't fully cured when the rest of the house was
built above it;
Building codes in most areas
requires cross-ventilation in a crawl space equal to at least 1.5
percent of the square foot area within the crawl space.
In addition, a ground cover
of 6-mil polyethylene sheets (preferably black-clear will sometimes
sweat) should be placed over the entire area of the crawl space soil,
lapped at least 6 inches and held in place by bricks or other weights.
(Black polyethylene works better than clear, because the black plastic
slows the growth of plants, which can occur even in a relatively dark
crawl space. In addition, some wood flooring manufacturers are now
recommending 8-mil poly in lieu of 6-mil.)
In cases where concrete is
poured to create a floor in the crawl space, the 6- or 8-mil
polyethylene cover is still required.
Capillary action causes
moisture to travel upward into the slab. Gravel beneath the slab can
slow the movement of moisture, but 6-mil plastic below the slab will
provide a more effective vapor retarder.
CAPILLARY RISE OF GROUND
MOISTURE: Moisture travels upward by capillary action--as much as 14
to 18 gallons per day have been noted under a 1,000 square-foot
house--and evaporates within the crawl space. Capillary rise occurs in
nearly all areas where the soil is clay or silt.
Capillary action is the
effect of surface tension that causes water to rise up a narrow tube,
against the effect of gravity. In building construction, capillary
action can occur between two surfaces placed together, or within porous
materials. This relates to the installation of wood flooring in that
moisture can be drawn through both the subfloor and the concrete below
It is best not to build
below the highest expected water table, for to do so is to have water
under pressure trying to enter through any crack or weakness in the
construction. Porous granular filling material around and under the
building, and connected to drainage lines, can be used to divert
drainage water away from the structure.
Making these adaptations is
the responsibility of the general contractor. However, the flooring
installer who has been hired by the general contractor to do the floors
in a new home or building should be aware of these details.
MOISTURE FROM THE HOUSE:
There are many sources of moisture from within the house. Mopping the
floor in a 150-square-foot kitchen can release the equivalent of 4 1/2
pints of water into the air a shower or bath about 1/2 pint; washing the
dinner dishes about 1/2 pint. Also, a family of four gives off about 1/2
pint of water per hour just breathing (this is why bedrooms are
unexpected moisture sources). As moisture is released in a house, it
moves to all rooms by natural air movement or by forced air movement
from furnace or air conditioning.
MOISTURE FROM MECHANICAL
SYSTEMS: Moisture is sometimes introduced into the crawl space from
the mechanical systems within the house. To avoid this, make sure the
clothes dryer is vented to the outside. Also, condensated water from
cooling systems and water from automatic ice makers should be discharged
away from the building.
When humidity increases, the effect on the wood floor can be damaging.
This occurs most frequently in homes in which occupants are there for a
short period of time, such as a weekend home or vacation cabin, or in
rooms that are closed off (not heated) to save energy.
If air conditioning or
heating is not used or is shut off, ventilation is a must even when the
home is not occupied. Otherwise, the floor will expand in the high
humidity, and cupping and buckling will occur. This "greenhouse
effect" will be exaggerated even more when a plank floor has been
installed, because wider boards react to moisture with more movement.
Minimizing moisture from
A heavy moisture invasion
can seep up through a wood subfloor. It may occur slowly, but its
effects are damaging. Proper installation of flooring calls for checking
subfloors for moisture.
To protect against moisture
rising through subfloors, the installer needs to make sure there is a
proper moisture-vapor retarder.
In any case, the moisture
content of solid strip flooring should be within 4 percentage points of
the subfloor. (That is, if the subfloor is measured at 10 percent
moisture content, the strip flooring should have no less than 6 percent
moisture content and no more than 14 percent.) For solid plank flooring,
the difference should be no more than 2 percentage points. Solid strip
or plank flooring requires a felt paper moisture retarder between the
floor and subfloor. If a wood subfloor is laid over an existing slab,
the moisture retarder can be cemented to smooth, clean-swept concrete.
In joist construction, a
vapor retarder of 15-pound saturated felt paper should be laid between
the wood flooring and the wood subfloor. If the wood subfloor is laid
over a concrete slab, the felt paper moisture retarder can be cemented
to smooth, clean-swept concrete. Other vapor barriers or retarders may
also be appropriate over concrete slabs.
Minimizing moisture from
concrete: Traditional construction of homes tend to have regional
variations. While many of the older homes in New England, the
Mid-Atlantic and Midwest regions have basements, most Southern
homebuilding is done on concrete slabs. The slab rests on a carefully
prepared base and is usually surrounded by a footing that runs below the
frostline, providing the actual foundation for the house.
The no-basement design
eliminates many of the moisture problems associated with basements and
below-grade features, obviously. But the installation of flooring over
concrete is not without its own intricacies. Concrete appears to the
untrained eye to be a solid, impermeable foundation, yet it's actually a
source in itself for moisture. Concrete expands when it absorbs moisture
in humid weather or by exposure to rain, and it contracts again when the
ALL concrete surfaces
regardless of age or grade level will emit or conduct some degree of
moisture, usually in the form of a vapor. This is a very natural and
necessary function of healthy concrete-it's like continual
"breathing." However, too much moisture emission without a
proper moisture barrier has resulted in flooring failures. Many times
the blame for this is placed on a faulty product, improper specification
or faulty workmanship, when the real reason lies with slab vapor
Moisture conditions are not
the flooring contractor's responsibility. Yet, the contractor should
take the initiative to determine potential problems and advise the
customer of available remedies before the start of installation.
Concrete is composed of
crushed rock, gravel, sand, cement and water. The introduction of water
into a cement batch will begin a series of perpetual chemical
interactions. The basic recipe for building concrete is completely
dependent on water being present in the slab.
Water in concrete is
necessary to continue the process of cement curing well past the first
few critical weeks. Therefore, all slabs should be tested for moisture
before the floor's installation.
Both on-grade or below-grade
slabs need time to both cure and dry out enough to handle flooring.
General guidelines suggest that 60 days is sufficient for the curing to
occur, and floors can be installed after this. These figures, however,
are influenced by a number of variables, and should not be used as the
sole criterion as to whether or not it is safe to install a floor.
Above-grade slabs poured in metal pans take significantly longer to dry
and have been known to require several months to well over a year to be
safe to install upon. Since drying times are influenced by many factors,
it is necessary to conduct proper moisture tests regardless of the slab
age or grade level. Testing
concrete for Moisture or see Moisture Detection Equipment
Because moisture can rise
through concrete by capillary action, moisture-vapor barriers and
moisture retarders need to be part of the installation process. Laid
between the base of gravel or crushed stone and the slab, this barrier
is usually in the form of heavy plastic, uninterrupted film. This film
prevents the penetration of moisture through the slab to the interior
surface, where it can ultimately damage hardwood floors.
moisture barrier or retarder should be placed on top of the slab before
installation. A few choices for the barrier are:
1.) Low end PVC vinyl
applied over the slab in multipurpose adhesive with seams sealed and the
surface prepared before spreading the wood adhesive. The use of this
method requires dependence upon the water-soluble, multipurpose bond in
the presence of moisture and wood adhesives that are accepted over
vinyl. This may also require a vinyl blocker.
Polyfilm-6-millimeter polyethylene film in 36-inch or 48-inch wide
rolls-applied over a "skim" coat of asphalt mastic. The mastic
should be troweled with a straight-edge trowel to skim coat the slab,
with coverage of about 80-100 square feet per gallon. After about 30
minutes, during which the solvents flash or evaporate, the polyfilm can
be rolled over the mastic by walking over the film, embedding it in the
mastic. Air bubbles that form under the film can be forced out toward
the seams with a push broom.
3.) 15-pound roofing
felt in asphalt mastic applied with a notched trowel at the rate of 50
square feet per gallon. A second similar coating of mastic and asphalt
felt should be added, with overlaps staggered to achieve a more even
There are several other
moisture barrier systems available, including two-part epoxy, rubberized
electrometric membrane, and other sealing liquids.
In all cases, installers
must verify acceptability of a particular system with the flooring
manufacturer, and also verify adhesive compatibility when planning to
glue down over any moisture barrier. If you are not familiar with the
system, check with the adhesive manufacturer, the flooring manufacturer
and the manufacturer of the moisture barrier system before attempting an
installation. Bottom line, if you even suspect a problem with moisture
DO NOT start the installation.