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CONSTRUCTION INNOVATION Volume 11, Number 3, Sept. 2006
Building envelope and structure
NRC-IRC completes pilot project aimed at developing high-performance stucco
It's impossible to drive through a new suburb without noticing the rise in popularity of stucco, or portland cement plaster, as an exterior finish. Relatively inexpensive, durable, attractive — it makes a fine finishing for a home. Unfortunately, on some occasions, wood-frame exterior walls with a stucco cladding have failed to perform up to design expectations in locations with heavy or sustained rainfall.
Thanks to researchers in NRC-IRC's Building Envelope and Structure program , however, a solution may not be far away. Working in cooperation with the Canada Mortgage and Housing Corporation (CMHC), they have completed a pilot project looking into the feasibility of developing a portland cement stucco material that will limit liquid water entry on its surface, while also allowing water vapour to dry out of it. Preliminary tests comparing the specifically engineered stucco materials against stucco materials commonly used in Canada suggest the project has promise.
To conduct these preliminary tests, the researchers divided the study into two parts. The first part focused on testing conventional stucco materials (those commonly used in Canada) to establish their performance in limiting liquid water entry and allowing water vapour drying to occur. The researchers looked at four stucco mixes, including one that satisfied the minimum requirement as stipulated in Canada's National Building Code (NBC).
The second part of the project focused on developing a new high-performance stucco material. The researchers put together four different stucco mixes designed to absorb less liquid water and allow more water vapour to dry out than conventional stucco materials. Previous NRC-IRC research had shown that stucco is one of the most influential materials on moisture management among the major components of a building envelope, which include stucco, a sheathing membrane, sheathing board and a vapour barrier. In addition, it has shown that a stucco material's ability to resist liquid water absorption and encourage water vapour drying positively influences overall moisture management in exterior wood-frame stucco wall assemblies.
An interesting MEWS off-shoot This pilot project and others like it are part of a larger project resulting from NRC-IRC's Consortium for Moisture Management for Exterior Wall Systems (MEWS). (Go to http://irc.nrc-cnrc.gc.ca/bes/hmpe/mews/index_e.html for more information about MEWS.) In it, NRC-IRC researchers are using the information gained from MEWS on the ability of certain wall systems to manage moisture sources and modifying construction materials to meet identified needs. This new project is part of a larger effort at NRC-IRC to develop advanced, high-performance materials to deliver moisture management strategies for wall systems. These materials are intended to meet long-term performance and durability requirements for the wide range of climate zones across North America. |
The results from the preliminary testing suggest that two of the high-performance stucco materials investigated show promise for limiting liquid water entry while also allowing water vapour to dry out. Because these are trial mixes, however, further research and refinement of the mixes is necessary. In future investigations, the researchers will carry out further numerical modelling to optimize the hygrothermal properties of the high-performance stucco materials, develop the most suitable mix design, and evaluate the long-term performance of the materials in a field study.
If you have specific questions on this project, or if you are interested in participating as an industry partner, please contact Dr. Phalguni Mukhopadhyaya at (613) 993-9600, fax (613) 998-6802, or e-mail phalguni.mukhopadhyaya@nrc-cnrc.gc.ca.
