Condensation is a serious concern for concrete floors when they are covered by additional flooring material, such as laminate planks. Concrete floors are porous, which means that moisture can pass through them easily. Moisture and vapor barriers are installed both beneath and above concrete to stop moisture problems. All vapor barriers are designed to prevent the transfer of water in the air, but moisture barriers are thicker materials designed to prevent flowing water as well. Materials can perform both functions, and you may have barriers under concrete as well as on top of it. If you have condensation problems underneath the moisture barrier that covers your concrete, this means that air flow is not free enough to ventilate the surface.
Moisture Moving from Under the Floor
If you have moisture that is seeping up to the moisture barrier beneath your laminate floor and becoming trapped there, this is a sign that your concrete floor is improperly protected against moisture. There may not be a vapor barrier beneath the concrete itself to prevent moisture from moving through it. The vapor barrier may also be too strong, allowing moisture to pass into the concrete but then trapping it there beneath the moisture barrier you have installed under your laminate flooring. Changes in heat will amplify this problem.
Moisture buildup in your concrete floor will not harm your laminate layer if the moisture barrier between it and the concrete is properly installed. But it will cause damage to the concrete itself if it cannot escape. Constant moisture without an outlet can cause concrete to crack with temperature changes. The heat can also encourage decay and mold growth in the porous surfaces of the concrete, which will lead to permanent damage.
Changing Outside Insulation
If you can add a layer of insulation to the outside of your house, especially around the rooms where you have installed the laminate floor, this may alter the pressure and moisture levels of the room enough to keep condensation from forming. Moisture barriers in the walls will keep water from flowing from the outside of the house into the floor, while vapor barriers with prevent humidity from passing in the air flow. These barriers are installed as part of wall insulation. While this will not offer direct protection for the concrete floor, it can help change moisture and heat levels in the room and lessen the severity of the problem.
The source of your condensation problem lies underneath the concrete itself. If you want to remove the condensation, you may need to replace the whole floor with a new slab that has a proper vapor barrier underneath it. You may be able to stain or etch the concrete itself, which does not require a secondary moisture barrier and will not trap water as much.