Summer Time
During warm and humid summers when indoor humidity can rise up to 90%, the opposite occurs.
Wood and bamboo absorbs moisture from the air and expands as a result. Even just a few days
of exposure to high humidity can cause wood flooring to cup. When a floor board cups, its edges
are higher than its center. Cupping can also happen when spilled water is absorbed by the floor.
Once cupping has occurred, it takes a while for the floor planks to restore its internal moisture
and flatten out.
When extensive moisture or humidity causes the floor to expand significantly, adjoining boards
start pressing against each other. In extreme cases, this increased pressure can cause the
affected boards to lose their structural integrity and crack. To avoid cupping, keep indoor
humidity level in your home or job site (prior to hardwood installation) within 40-65% range.
Never allow indoor humidity to rise over 65%. Maintain optimal humidity levels by keeping air
conditioner or dehumidifier running during hot humid summer weather.
KNOW YOUR WOOD OR BAMBOO FLOOR
Wood Flooring Expansion and Contraction
Unlike many floor coverings, wood and bamboo floors can last the lifetime of the building in
which they are installed. Home owners who want them to last that long, however, should note the
number one enemy of a hardwood and bamboo floors:
moisture
. Wood and bamboo floors
naturally expand when moisture is present and shrink when it is not. Whether the reactions are a
problem or not depends on the severity of the situation. Following are some of the common
results when water and wood floors combine
.
CRACKS BETWEEN BOARDS:
Almost every wood and bamboo floor endures some expansion
and contraction as seasons and humidity levels change. When homes are heated, humidity
levels plummet, boards shrink and spaces appear between the boards. In dry months, cracks
can easily develop to the thickness of a dime on a typical solid 2¼ inch oak floor, with light-
colored woods making the cracks appear larger. Plank floors also will show cracks more. These
spaces are to be expected and usually close up as the season changes and moisture returns to
the air. To reduce the degree of change, home owners can add moisture to the air during the dry
months, ideally by installing a humidifier in the furnace or air conditioner.
