There are several good reasons to seal your concrete basement floor. Not only will the sealant protect the floor, but it will also make it last longer. To determine whether you need to add sealer or apply a new layer, examine your floor for water marks which indicate that water has seeped through your floor and then evaporated or drained. Next, use a radon gas detector to determine if gas is rising through your basement floor. Finally, look for open joints between the floor and the walls. Check for cracks in your floor that might be allowing water to enter.