Specifiers often require concrete floors to be placed directly on a vapor retarder to reduce inflow of moisture from the subgrade soil and provide long-term protection for moisture-sensitive floor coverings. Water-vapor emissions as high as 100 pounds/1,000 square feet/24 hours have been measured over soils. Covering the subgrade with a vapor retarder can help reduce emission rates from concrete-floor surfaces to the 3 or 5 lbs/1,000 sf/24 hrs typically required by floor-covering installers. But what happens if the vapor retarder is punctured or installed incorrectly?
To answer this question, The Aberdeen Group performed calcium-chloride cup tests on vapor retarders with and without holes. This article presents the results of these tests, which show that punctures or other openings in a vapor retarder can significantly increase water-vapor emissions through concrete floor slabs. It also discusses ways contractors can avoid damaging the vapor retarder during slab construction.