A dirty mop cover may leave traces on the floor. Replace it with a clean one. The dirty cover can be machine-washed like any terry cloth towels. Place doormats outside and rugs inside at every entrance of the house, again to prevent sand or abrasive dust from accumulating on the floor. Place a rug in front of the kitchen sink, kitchen working stations, and the dishwasher to protect the floor from dropped kitchen accessories and from water or oily detergent spills.
Hardwood is a living substance which reacts to changes of relative humidity.
It absorbs or releases humidity according to seasons. Consequently, its dimension changes. In summer, when humidity is at its highest, it is absorbed by the wood which then expands. These variations can be minimized with proper ventilation, dehumidifying or heating. In winter, on the other hand, when the heating system is on, the relative humidity level in the house is much lower.