Words: Andrew W. Wagner, P.E. Senior Engineer, Division Manager, WDP & Associates
Photos: Breedfoto,
Moisture is an overwhelming post-occupancy issue faced by the construction industry. In recent years, studies have indicated that over 80% of all building insurance claims are related to moisture issues, and of those claims over 80% result from building envelope issues¹.
While brick masonry veneer is not the single cause of moisture-related issues, it is often one of the many components that must be coordinated and installed properly to ensure the building envelope performs successfully.
In North America, masonry cavity walls came into popularity around the 1920s, promising a better way to manage moisture penetration and floor and roof loads, and expediting construction schedules as compared to mass masonry wall construction. The design methodology has changed over the years to incorporate different flashing materials, moisture barriers, air barriers, and insulation.
However, the basic premise for the management of bulk water remains the same. An outer masonry veneer acts as a first line of defense to limit moisture infiltration, and a cavity, coupled with flashing elements, is used to manage the water that passes through the veneer and directs it back to the exterior. Although the veneer and flashings are critical aspects of cavity wall construction, these two items are rarely given the focus they deserve.
For many projects, brick masonry veneer design and construction have become prescriptive processes. Industry-recommended best practice, prescriptive Code language, and manufacturer recommendations drive many of the design and construction activities. Additionally, there seems to be a notion that since brick masonry veneers are permeable and allow water infiltration through the mortar joints, the primary concern related to water infiltration is the proper installation of the air and moisture barrier.
While air and moisture barrier installation is important, the veneer still serves as the first line of defense against bulk water infiltration. As a result, it is important to understand the aspects of the installation that can result in increased water penetration through the veneer, and make decisions accordingly to help prevent overburdening the cavity wall drainage systems.
Water penetration through a brick veneer can be determined through laboratory testing in accordance with ASTM E514, or field testing performed in accordance with ASTM C1601. Neither standard outlines the acceptance criteria for water penetration rates. However, there have been publications that draw comparisons between water penetration rates determined using ASTM C1601, and buildings that experienced moisture-related issues. One such publication indicated that buildings that have a water penetration rate through the veneer in excess of 0.83 liters per hour per square foot (L/hr/sq.ft) of veneer tend to have water infiltration issues².
There are a variety of corollaries and connections that can be drawn from many of these studies, but perhaps the most notable is the impact the veneer plays on the overall performance of masonry cavity walls. In essence, the veneer controls exposure, and while it will not rectify deficiencies in the building moisture barrier or drainage systems, the veneer controls how much water reaches such deficiencies.
Thus, brick veneer is a primary component of a cavity wall system controlling the severity of the issues that result from moisture barrier and flashing deficiencies. Ensuring brick veneers are constructed to limit water penetration through the veneer is a critical step in limiting the potential for moisture issues.
Water penetration through brick veneer is primarily a function of workmanship and the material properties of the mortar and brick. On many projects, the necessary requirements for proper workmanship and material properties are covered in boilerplate specification language, yet on many projects, these requirements are overlooked or given little oversight.
Workmanship is a key element in limiting water penetration. Joints should be fully filled with mortar and tooled to facilitate better bond and compress the outer face of the mortar joint. Most project specifications outline requirements for filled mortar joints and proper tooling. These steps help limit gaps and avenues for water migration through the veneer, thus reducing the water penetration through the veneer.
Similarly, most project specifications reference ASTM C270 and ASTM C216 for mortar and brick requirements. Generally speaking, materials complying with these standards will result in brick and mortar compatibility. This means that the water retentivity of the mortar is compatible with the initial brick rate of absorption (IRA or suction) to facilitate proper bond and limit bondline separations.
Bondline separations are gaps along the interface between the mortar joint and brick that occur either due to a lack of moisture sharing between the brick and mortar or the brick pulling excessive amounts of moisture from the mortar at the time the brick is laid. Again, these gaps are avenues for water penetration, and since they tend to be the result of the material properties, they are generally systemic issues on a project that result in excessive water penetration through the veneer.
Additionally, most specifications will allow the use of brick that is found to have an IRA above 30 g/min/30 sq.in. if the brick is properly pre-wetted to achieve an IRA below 30 g/min/30 sq.in. at the time the brick is laid.
All that said, it is not uncommon to walk a jobsite and see head joints that are partially filled. Additionally, since the veneer is a defining characteristic of the building appearance, requirements are often incorporated into a project without proper consideration of the performance impacts. Desired aesthetics often dictate the profile of tooled joints.
Even though concave, “V,” and grapevine joint profiles generally provide the best resistance to water infiltration³, many projects require extruded joints or other profiles that typically do not provide as great of resistance to water penetration. Furthermore, many projects use brick with an IRA above 30 g/min/30 sq.in. However, few projects have a pre-wetting plan that is submitted, verified through field testing, and spot-checked throughout construction to ensure the pre-wetting procedures are adequate and followed.
Also, many projects elect to use thin brick systems based on cost, schedule, or access benefits, but it is important to note the smaller bedding planes of this system often result in greater water penetration rates than conventional brick veneers. In summary, standard specification language must be updated to align with the material properties and installation requirements associated with the project-specific requirements.
So what does this mean? The desired goals, materials, and installation practices for the project should be evaluated to determine whether additional modifications are appropriate. Systems or joint profiles that are known to have a higher water penetration rate through the veneer are not necessarily unsuitable, but consideration should be given to the potential impacts of more moisture passing through the veneer.
Additionally, over time as the joints in the veneer weather, the water penetration rates are going to increase, and this should also be evaluated as part of the design. Specified end dam heights should be evaluated based on the anticipated building service life, anticipated drainage, and long-term drainage performance of the specified weeps.
Many specifications indicate that end dams should be provided, but a minimum dimension for the end dam height is often omitted for typical through-wall flashing conditions. Vertically oriented flashings or closures should also be specified and detailed at fenestration integrations or transitions between veneer cavity wall conditions and barrier wall conditions to manage the lateral migration of moisture and ensure continuity of the building air and moisture barrier.
Furthermore, if the design parameters are likely to result in a veneer that has a high-water penetration rate, consideration should be given to the incorporation of added redundancy into the moisture barrier and drainage systems. Simply put, if the veneer is doing less to prevent moisture exposure, it is increasingly prudent to ensure a single mistake does not become a direct path for water infiltration to the interior.
Lastly, consider the need for additional submittal and field quality control requirements. The incorporation of mock-up and ASTM C1601 testing can be a valuable tool for the project in determining the anticipated water penetration through the veneer. If coordinated early in the project, the information gathered from mock-up testing can be used to aid in the final approval of materials and installations.
It is also recommended that a process be outlined if a brick with a high IRA is used to ensure pre-wetting procedures are field verified to determine the resulting IRA. The process should also outline requirements for periodic verification of IRA throughout the project to ensure changes in temperature do not impact the effectiveness of the pre-wetting procedures. Additionally, pre-wetting procedures should be evaluated and altered as necessary to prevent brick units from freezing.
Ultimately, the key is recognizing that limiting bulk water penetration through brick veneers is dependent upon the sum of multiple parts. Although the veneer is not the primary moisture barrier, it plays an important role in limiting the potential for moisture issues and thus should be given the proper consideration.