Solid wood floors are one solid piece of wood that have tongue and groove sides and come in either pre-finished or unfinished styles. Solid wood floors are sensitive to moisture and it is not recommended to install these floors below ground level, or directly over a concrete slab. These floors are for nail-down installations only. You can refinish, or recoat solid wood floors several times, which adds to their appeal and to their long life. There are solid floors that are over 100 years old and are still in good condition.
All solid wood floors will react to the presence of moisture. In the winter heating months, moisture leaves the wood causing the floor to contract which leaves unsightly gaps between each plank. In the summer months when the humidity is higher the wood will expand and the gaps will disappear. If there is too much moisture it may cause the wood planks to cup, or buckle. This is why it is important when installing a solid strip floor to leave the proper expansion area around the perimeter and to acclimatize the wood prior to installation.