The transport of water through waterproofing membranes over concrete substrates resulting in water-filled blisters and leaks has been demonstrated by the authors to be caused by osmosis. Although this issue has now been studied for more than a decade, there is currently no industry standard to test for the risk of osmosis in waterproofing membranes. The authors have developed a protocol to measure the osmotic flow and evaluate the risk of osmotic blistering in waterproofing membranes including a standardized osmotic flow rate test, ASTM E96, Standard Test Methods for Water Vapor Transmission of Materials, inverted wet cup vapor permeance testing, and modified ASTM long-term absorption testing. This testing protocol has measured osmotic flow rates and ASTM E96 inverted wet cup vapor permeance for a range of different waterproofing membrane types. The authors propose that this set of testing protocols or another proxy test be adopted by ASTM to determine the risk for osmosis, including thresholds above which a membrane may be deemed “high risk.” 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 proposed protocol, an ASTM E96 inverted wet cup vapor permeance less than that of the substrate (i.e., less than 0.1 US perms on a concrete slab), and minimal long-term water absorption uptake. In addition to these thresholds, the long-term aging effects of the membrane should be determined.
This is a preprint of an article published in STP1617: Building Science and the Physics of Building Enclosure Performance, Copyright @ 2020, ASTM International, West Conshohocken, PA, 177-194, http://doi.org/10.1520/STP161720180085