Cold-applied, liquid waterproofing and roofing membranes are used on concrete podium slabs, roof decks, and planters in protected roofing applications. They’re made from various materials including polyurethanes, polyureas, and asphalt modified urethanes.
Liquid membranes are preferred in these applications for their relative low cost, as well as their ease of application over complicated curbs, planters, water features, penetrations, and interfaces. While cold-applied membranes have distinct benefits in these applications, they have also had their share of problems.
Over a decade ago, while performing warranty reviews and condition assessments, RDH began to find water-filled blisters under many new cold-applied membranes. In some cases it was so severe that the premature replacement of entire roof assemblies was necessary.
Our initial research into this phenomenon found that water filled blisters become visible within the first 5 years of service and progressively got worse over time, growing in size until entire roof areas were consumed. Water leaks to the interior also occurred, and pavers and other landscape components were displaced or found ‘floating’ on the blisters.
The cause of the water filled membrane blisters had the industry scratching its head. A wide range theories were introduced, including:
- Inadequate membrane thickness
- Poor workmanship
- Outward vapor drive
- After disproving many of these supposed causes, RDH set out to research and determine the physical building science mechanism responsible.
The research work took led us to a series of field studies and building monitoring projects, as well as several iterative laboratory experiments. After months of analysis, RDH discovered that the water transport process of osmosis was responsible for causing the water filled blisters. Osmosis does not commonly affect building enclosure assemblies, so finding it as the phenomenon responsible was unexpected and pivotal to our investigation.
Osmosis is the process of water transport through a semi-permeable material (eg. liquid roof membrane) due to the difference in dissolved salt concentration (eg. dissolved salts in concrete below membrane and rainwater above).
As part of our research, the semi-permeable nature of many waterproofing membranes was measured. We also looked at salt concentrations within the blister water, and finally, measured the flow of water through various membranes.
Through several years of subsequent research we developed and refined a three-part laboratory test procedure to assess the potential for osmosis to occur through membranes. Independent third party testing and several peer reviewed scientific research papers have been published on the study and the findings to date. The work has also been published in building science textbooks.
Since confirming the process of osmosis, we have worked with numerous roofing and waterproofing membrane manufacturers to test and to help develop more osmosis resistant cold-applied waterproofing membranes. Ongoing research and testing continues to this day with new cold-applied membrane chemistries. We have also helped numerous owner groups repair affected membranes and install more robust long-term solutions into their buildings.
“Well Done! Finally an Explanation for four failures I have seen over the years in the San Francisco Bay area”
Industry Comment from RCI Presentation
San Diego, California