Cold applied liquid applied waterproofing and roofing membranes of various chemistries (e.g. polyurethane, polyurea, polyester, and asphalt modified urethanes etc.) have become increasingly popular in past decades, particularly over concrete podium slab, roof decks, and planters in protected (i.e. inverted) roofing applications. Liquid membranes are often preferred in this application for their relative low cost, ease of application over complicated curbs, planters, water features and at penetrations and interfaces. While cold-applied membranes have their benefits in waterproofing – they have had their share of problems.
Over a decade ago, the roofing industry began to find systemic water-filled blisters under many of these cold-applied membranes, in cases so severe that the premature replacement of these membranes has now become commonplace. Field studies have shown that these water filled blisters become visible within the first 5 years of service and progressively get worse and grow over time with expanding pressure until entire roof areas are consumed. Water leaks occur with time and displaced or floating pavers and other landscaping components are also a common side effect. A decade ago, the cause of the blisters had the industry scratching its head and a wide range excuses from inadequate membrane thickness and pin-holes, detailing, shoddy workmanship, to outward vapor drive were supposedly to blame.
Being curious as to what was actually causing these water filled blisters to form, a study was initiated to find the physical building science mechanism responsible. This study encompassed field studies, building monitoring, and several iterative laboratory experiments, until eventually the water transport process of osmosis was confirmed. This presentation covers the story of how the phenomenon of osmosis was discovered, the physical mechanism of osmotic blistering and the scenarios where it can occur, and the new testing protocol developed. The test results for a wide range of new and aged membranes commonly used within the roofing and waterproofing industry will be presented along with recommendations for the material properties needed to prevent blistering from occurring.
Graham is a Principal and Building Science Research Specialist with RDH. He has a passion for technology and for making better and more energy efficient buildings. He leads RDH’s building science research group and is actively involved in a wide range of projects from building research studies to forensic investigations, building monitoring, hygrothermal modeling, and new construction across North America. Graham has authored several publications and practical industry guideline documents related to durable and energy efficient building enclosures. In addition to RDH, Graham is a part-time instructor at the British Columbia Institute of Technology where he teaches building science courses to students at the Diploma and Masters levels.