Moisture and humidity cause wood to expand. When this moisture is removed, the wood contracts. If the floor is not installed to allow for this natural movement, splitting of individual boards will occur around the edges and at the joints. A professional installer will typically leave a small amount of space around the edges of the floor to allow for natural expansion. This type of splitting cannot be repaired once it occurs. Replacing the split boards is only a temporary fix. Because the floor hasn’t been installed properly, it will lack the room it needs to move, and the boards will split again.
Splits in hardwood flooring are often caused by excessive or rapid drying. If the moisture content is reduced to less than 4 percent, the grain separates, causing splits. Minor cracks are common as a floor ages. As moisture is absorbed back into the wood, the grain expands again, and the cracks may disappear. Dryness that causes major splitting in the boards should be addressed and repaired.
A sudden change in humidity can cause splitting in both newly installed and older hardwood floors. The boards can’t withstand the stress of the rapid expansion or contraction, and they split. The only repair for this type of splitting is to remove the source of humidity and to replace the damaged boards.
If the cause of the splitting in your wood floor is high humidity, a dehumidifier is often enough to prevent further splits until you can remove the source of the moisture. Inspect your ductwork, as well, to eliminate the possibility of excessive drying, particularly if the splitting is limited to one area of the floor. A damaged duct can leak hot air on one area of the floor, drying it out and causing cracks. When the cause of the damage is repaired, sand the floor and fill the split boards before sealing.