My wood, bamboo or cork floor is not laying flat:

Cupped Floor
Cupping occurs when the edges of a boards are high and its center is lower. The floor will not be flat and the wood will have a “wash board” appearance.

Cupping is caused by a moisture imbalance through the thickness of the wood: The wood is wetter on the bottom of the board than on the top. The moisture imbalance can be proven by taking moisture meter readings at different pin depths.

Cupping is caused by a moisture imbalance through the thickness of the wood: The wood is wetter on the bottom of the board than on the top. The moisture imbalance can be proven by taking moisture meter readings at different pin depths.

Crowning is the opposite of cupping: The center of a board is higher than the edges. Moisture imbalance is sometimes the cause of crowning if excessive moisture is introduced on the top of the floor, perhaps from water used in maintenance or plumbing leaks from an overhead sprinkler system. However, a common cause is that the floor was previously cupped, but was sanded at the wrong time-before the moisture content returned to normal and the board flattened on its own.

It should be noted that some slight cupping and crowning may occur naturally, and should be tolerated: largely seasonal in occurrence, it’s common in wider planks.