• ELYSE HENDERSON
    RDH Building Science
  • BRIAN HUBBS
    RDH Building Science
  • GRAHAM FINCH
    RDH Building Science

Waterproofing membranes are widely used in the building industry as a barrier for water entry into a building enclosure. Over the past two decades, waterproofing system failure due to osmotic blistering has occurred in some protected membrane/inverted roofing assemblies. Not all waterproofing membrane assemblies are at risk for this process and the authors have developed a test protocol to establish the relative risk level of waterproofing membranes to osmosis. Using this protocol, the osmotic flow rate of SBS, hot rubberized asphalt, PMMA, EPDM, TPO, HDPE, polyurea, asphalt emulsion, asphalt-modified polyurethane, and various other 2-component cold applied membranes was measured to determine a threshold osmotic flow rate for low risk waterproofing membrane systems.

In this research, a wide range of osmotic flow rates were obtained for the various membrane types. Most asphalt-modified polyurethane membranes consistently exhibit osmotic flow rates significantly higher than the low-risk threshold of ~0.0 g/m²/day (typically 1.4 to over 20 g/m²/day) after data corrections, which results in osmotic blistering and premature membrane failures. Some polyurea and asphalt emulsion membranes have flow rates above 2.0 g/m²/day with unknown long-term performance, while most other membranes that were tested have flow rates around 0.0 g/m²/day after data corrections from control samples. To reduce the potential for osmotic blistering over concrete, it is recommended that waterproofing membranes used in inverted roofing assemblies should have an osmotic flow rate near 0.0 g/m²/day when tested using the methodology herein, an inverted wet cup vapour permeance less than that of the substrate (i.e. <0.1 US Perms on a concrete substrate), and minimal long-term water absorption.

Presented at the 15th Canadian Conference on Building Science and Technology.

View presentation slides here.

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