With respect to overcladding masonry, the act of repairing and smoothing the existing wall by parging, as well as by tending to and sealing cracks in masonry and mortar, results in an enhanced air barrier function. This is further improved with the installation of a fluid-applied vapour barrier within the overclad assembly, creating an additional impediment to the movement of moisture through the system. To state plainly, the air barrier is not a single component of the enclosure assembly. When thinking of the air barrier, one should think about the flow of air through the assembly in total, as an integrated system.
How much air should pass through the enclosure? Typically, the answer is none. To the definition that an air barrier should be continuous, structural, and uninterrupted, according to Wagdy Anis, FAIA, writing for the Whole Building Design Guide. As he stated, the enclosure and the overcladding layer should address three types of air leaks through an architectural enclosure:
- Orifice flow, e.g. in a slit unintentionally left between a window rough opening and its frame.
- Diffuse flow, such as through some brick or concrete block.
- Channel flow, the common type of air leaks where the air entry point and exit point are distant from each other, giving the air enough time to cool below its dew point and deposit moisture in the building enclosure.2
Taken together, these principles help to effectively design and specify overcladding for one of the most common challenges faced by long-term building owners: poorly performing and unattractive masonry walls. Failure modes in masonry facades where the masonry wall is supported from steel lintels begin with age alone and can be exacerbated by older practices, such as missing or ineffective masonry expansion joints. Some cavity wall construction may lack thermal insulation as well.
Thermally displaced masonry will result from the lack of expansion joints, which may be visible in brick facades. In extreme cases, these may impact glazing systems. Some exterior walls may not even comply with modern codes for resisting lateral imposed loads.
Questions about EIFS overcladding
The original article also included some discussion of exterior insulation and finish system (EIFS) applications as an effective and frequently utilized approach for face-sealed overcladding to address aging or inadequately designed masonry facades. However, there is an interest in knowing whether there has been any skepticism or criticism of this approach among industry professionals, whether based on the technique or performance outcomes. The best answer is, there should be, depending on the particular EIFS product and application techniques utilized.
First developed and marketed in the 1970s, this once novel system has evolved quickly with greatly improved efficacy in more recent iterations. There continue to be some contractors and trades groups in the marketplace who may incorporate outdated systems and products in their solutions offered, but these must not be used for exterior overcladding of masonry in part because some of those systems provides no means for moisture management, including draining or drying of the system.
