During warm and humid summers, when indoor humidity can rise up to 90%, the opposite occurs. Wood absorbs moisture from the air and, therefore, expands. If wood flooring is exposed to extensive humidity even for a couple of days, it can cup. Cupping means that edges of a board are higher than its center. It can also occur after water is spilled onto the floor and is absorbed by the wood. After cupping has occurred, it takes a while for humidity to return back to normal. It is very important to be certain before installation that humidity level on the job site is within allowed range 45-55%. In extreme cases, if wood expands significantly, boards get under enormous pressure from adjoining boards. As a result, boards can lose structural integrity and crack. To prevent cupping do not allow humidity rise over 60%. Keep air conditioner or dehumidifier running during humid summers.
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