Isolation Sheets Covering Self-Adhered Membranes May Enhance Drainage Under Cement Plaster Wall Claddings

March 30, 2011
Publication: Journal of Building Enclosure Design p 18-22
Author(s): Nicastro, Anthony J.

Abstract: The architecture, enginering and construction (AEC) industry does not fully understand the interaction between cement plaster, admixtures and the polyethylene facers of self-adhered membranes (SAM) and similar continuous membranes. Manufacturers of SAM, commonly referred to as peel-and-sticks, often recommend their products for use in cement plaster wall systems. However cement plaster can bond to the polyethylene facers of SAM, which may adversely affect drainage behind the cement plaster cladding.|We have also observed that cement plaster can bond to building paper and other water-resistive barrier (WRB) materials in a manner that can impede drainage. To mitigate the potential for bonding between cement plaster and building paper, industry members often include two layers. The space between layers can serve as a plane through which water can drain. However, the industry has not yet standardized the provision of an isolation sheet when using polyethylene-faced SAM or similar continuous membranes as the water-resistive barrier (WRB). The industry presumes SAM alone is a sufficient water-resistive barrier.|We performed limited scope, preliminary testing of cement plaster samples to observe and evaluate the potential bond characteristics of cement plaster and compared the differences between assemblies using building paper and SAM. In addition, we explored the bonding effects of a common acrylic admixture, often used to reduce cracking in cement plaster.