Effects of Moisture in Concrete Roof Decks on Vapor Retarder Adhesion

Abstract

In recent years, the roofing industry has recognized, or some may say reaffirmed, the importance of installing a vapor retarder over concrete roof decks to protect the applied roofing system. If there is no vapor retarder on the concrete roof deck, moisture from concrete can migrate into the roofing system over time and cause significant damage. The moisture can accumulate in the layers under the roof membrane and cause deterioration and loss of strength of cover boards and facers on insulation boards. Other damage from moisture includes mold growth, degradation of water-based adhesives, and fastener corrosion. These problems can lead to loss of attachment, wind damage, or blow off. Installing a vapor retarder over the concrete deck can be effective in reducing the amount of moisture that migrates into the roofing system. Roofing system manufacturers and industry standards lack practical information about when the concrete is dry enough to install the vapor retarder and whether the moisture in the concrete will affect vapor retarder adhesion over time. Manufacturers say the concrete should be dry but do not define what dry is or how to measure “dryness.” To help the industry with this issue, we developed a testing program to evaluate the sensitivity of vapor retarder adhesion to the following variables: (1) age of concrete at the time of vapor retarder is applied and (2) pull-off strength of adhered vapor retarders over time. We prepared a total of 60 concrete samples and installed different vapor retarders at the following intervals after placing the wet concrete: 2 days, 7 days, 14 days, and 28 days. We tested the adhesive strength of the vapor retarder that was adhered at various time intervals after concrete placement and then at regular time intervals after the application of the vapor retarder for each time interval.