Slight color changes occur in wood floors gradually with time and exposure as a result of oxidation and/or photochemical activity.
Homeowners often notice a slight difference in height from one board to another on a pre-finished wood floor. This is called over-wood or lippage and is defined as the vertical distance between two abutting boards. Pre-finished boards are manufactured to be within a certain tolerance and may have a slight variation in height from board to board. Due to the fact that the boards are sanded at the factory prior to installation some deviation between the individual planks is unavoidable. Typically the boards come from the factory with a maximum deviation the height of a business card.
Some over-wood in a home is perfectly normal and does not indicate a flaw in the boards or unacceptable deviation in the sub-floor. Nor does it affect the integrity of the floor. According to the National Association of Home Builders’ Residential Construction Performance Guidelines, over-wood or lippage under 1/16 of an inch (about the size of a credit card) is considered to be within tolerance.
Cupping, or “washboard” is seen when, across the width of one piece of the flooring material, the edges are high and the center is lower. This condition usually develops gradually. Moisture imbalance through the thickness is the only cause. The material was manufactured flat and was flat when installed. Job site or occupant-provided moisture is greater on the bottom of the piece than on the top. Find the source of moisture and eliminate it. Common moisture sources and their corrections are:
Expansion is also the result of site moisture and may have moved the floor tight to vertical surfaces. If so, remove flooring along the wall, or saw cut, to relieve pressure. The ultimate cure is to allow time for the corrections to take effect, permitting the floor to improve on its own.
Gapping in solid wood floors cannot be stopped completely. Wood expands and contracts with changes in humidity. Using a humidifier during the heating months may help reduce the amount of gapping in solid wood floors. Also, some wood species may expand and contract less than others. Engineered wood floors are much more dimensionally stable than solid wood floors and will show little or no gaps between planks.