WHY IS IT PREFERABLE NOT TO POUR CONCRETE IN AN UNVENTILATED BUILDING?
Freshly poured concrete contains a tremendous amount of moisture (A 10 x 10 x 4 area of concrete contains approximately 24 gallons of water). As the concrete cures, much of this water is liberated into the air, increasing the relative humidity and vapor pressure within the building. Ventilation is the simplest way to reduce humidity and vapor pressure and also lower the probability of condensation related problems. Failure to adequately ventilate a building during and after a concrete pour can result in condensation on the surface of the vapor retarder and potentially within the insulation. This is particularly critical in colder temperatures. Vapor retarders do precisely as their name implies, they retard the passage of water vapor into an insulation system. They are not complete barriers that fully block the movement of moisture vapor. The amount of water vapor that passes through or around an insulation facing is a function of the following: • Perm rating- The lower the perm rating
