Wicking can occur when there is a breakdown of the vapor barrier installed beneath the concrete floor. Wicking can also occur if a vapor barrier was not installed prior to pouring the concrete. This occurs when water from the soil beneath and surrounding the concrete slab is absorbed by the concrete and moves to the surface. Wicking may be reduced by reducing moisture in the soil surrounding the concrete slab. This may involve adding a drainage system to reduce dampness in the soil surrounding the slab. If the concrete floor sweats after rain, the sweating is likely caused by wicking.
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Condensation occurs when the cool concrete comes into contact with warm, humid air. The moisture collects on the surface of the concrete, similar to dew on a cool morning or cold pipes in a basement, and appears to sweat. This moisture can be absorbed by the concrete and continue to release from the top of the concrete until the water has fully evaporated. Condensation can be reduced by using a dehumidifier in the room. If the concrete floor sweats during warm, humid conditions, the sweating is likely caused by condensation.
Salts in the concrete can attract moisture from humid air. Improper sealing or improper finishing can increase the occurrence of sweating caused by absorption of humidity. Absorption can be reduced or eliminated by applying a concrete sealant. Prior to sealing concrete, the concrete must fully cure and dry. If the concrete floor sweats during high humidity at any temperature, the sweating is likely caused by absorption.