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Abstract
Blistering in BUR membranes is typically related to two principal factors: voids or air pockets and moisture in voids or air pockets. The presence of moisture in the void, in addition to air, acts as a multiplier of the expansion forces. Moisture related blistering in BUR membraes occurs as a result of the interaction of three mechanisms: evaporation/vaporization; vapor diffusion; surface diffusion/capillarity. The migration of water through hygroscopic materials does not follow Fick's law. Water becomes absorbed and can migrate through hygroscopic materials in the absorbed phase by the mechanism of surface diffusion. The effect of the surface diffusion in moving moisture in the opposite direction to vapr diffusion on the formation of blister in BUR membranes is examined. The classic 1953 Hutcheon-Paxton experiment is revisited. Recommendations are provided on avoiding blister formation. Single-point, single-temperature vapor permeability measurements are shown to be inadequate for design and analysis purposes. A case study of a failed (due to blistering) and recently replaced 1 million ft sq roof is presented as part of the discussion.
Blistering in BUR membranes is typically related to two principal factors: voids or air pockets and moisture in voids or air pockets. The presence of moisture in the void, in addition to air, acts as a multiplier of the expansion forces. Moisture related blistering in BUR membraes occurs as a result of the interaction of three mechanisms: evaporation/vaporization; vapor diffusion; surface diffusion/capillarity. The migration of water through hygroscopic materials does not follow Fick's law. Water becomes absorbed and can migrate through hygroscopic materials in the absorbed phase by the mechanism of surface diffusion. The effect of the surface diffusion in moving moisture in the opposite direction to vapr diffusion on the formation of blister in BUR membranes is examined. The classic 1953 Hutcheon-Paxton experiment is revisited. Recommendations are provided on avoiding blister formation. Single-point, single-temperature vapor permeability measurements are shown to be inadequate for design and analysis purposes. A case study of a failed (due to blistering) and recently replaced 1 million ft sq roof is presented as part of the discussion.
Date
12/1995
12/1995
Author(s)
Joseph Lstiburek
Joseph Lstiburek
Page(s)
777-
777-
Keyword(s)
blistering; built up roof; void; air pocket;
blistering; built up roof; void; air pocket;