Importance of a Well-Drained Masonry Wall
By Gary Johnson
No masonry is truly waterproof, whether the result of capillary action, absorption or construction error. During the multi-decade life spans of typical high-quality structures, drainage in the cavity of a masonry veneer wall is necessary to minimize moisture damage and create a long-lasting, low-maintenance wall. Drying of the wall by promoting ventilation within the cavity is of increased importance, most recently due to the application of continuous insulation close to the exterior of the structure.
The impairment resulting from mortar dams of both water flow down to the weep system and airflow should be prevented. Specifying and installing materials that block mortar penetration while supporting water and airflow are important design considerations. A well-known answer to this issue is MortarNet®, developed more than 25 years ago. MortarNet is fabricated from a polymer mesh formed into a series of dovetails. Mortar droppings falling to the bottom of the cavity are captured at two levels, preventing the formation of a continuous blockage of the weep system. As a result, water and air are free to move through the device and within the cavity.
Adhered masonry veneers, such as manufactured stone, natural stone, stucco and thin brick, have the same moisture penetration and drying issues as brick veneer cavity walls. However, they have been slower to adopt proven moisture management techniques and continue to suffer from a high failure rate. DriPlane™ and WallNet® by Mortar Net Solutions are examples of polymer-based mesh products designed to create cavities behind adhered veneers to promote drainage and ventilation. This brings the same technical solution that has proven effective for brick veneers over decades to adhered masonry.
Performance test standards
ASTM 2925-14 Standard Specification for Manufactured Polymeric Drainage and Ventilation Materials Used to Provide a Rainscreen Function is the first attempt to define performance standards for the materials that promote drainage and ventilation in masonry walls. This standard was revised in 2017, and a subsequent revision is in process. Following are the key performance characteristics measured by ASTM E2925-17 and a summary of each.
Ventilation/Airflow Test. A test apparatus is built that confines a 1.2 m x 2.4 m (approximately 4’ x 8’) piece of polymeric material under test. The apparatus is airtight, except at the top and bottom. A calibrated pressure difference is created between the top and the bottom, and the airflow is measured and reported.
Drainage Test. An apparatus similar to the ventilation test is constructed. However, in this case, a calibrated amount of water is introduced into the top. The amount of water drained and the amount retained are measured and reported.
Thickness Test. A sample with a constant (and relatively low) weight to insure uniformity of measurement from sample to sample of materials with non-uniform surfaces is measured. A thickness of 5 mm (0.2”) has been shown to be adequate to sustain airflow and drainage. In thinner sections, the ventilation is reduced by interaction of air flow with the boundaries of the cavity.
Compression Test. Adequate performance demands that the material have sufficient strength to maintain structural integrity after insertion into the cavity. The compression test measures the thickness change of the sample under various loads.
UV Exposure Test. Materials after installation sometimes are left exposed to sunlight between their attachment and the installation of cladding. This test exposes samples to intense UV for a relatively short time to provide guidance on the allowable duration of UV exposure without significant degradation of the physical properties of the material. After the UV exposure test has been completed, the compression test is repeated to confirm that the strength has not been altered significantly by UV exposure.
Heat Aging. Heat aging is another test to confirm acceptable stability of material properties. Typically, material property degradation is faster during exposure to high temperatures that create accelerated aging. After the heat aging test has been completed, both the thickness test and the compression test are repeated to judge the change in these properties during exposure to elevated temperature.
Mold and Fungi Resistance. It is important that all materials used in a structure, especially those residing in high-moisture environments, be shown to resist mold and fungi growth. The test method of ASTM C1338 is required by ASTM E2925.
Water Exposure. While in the wall, the polymeric materials may have water present for an extended period. Therefore, important physical properties must be maintained after such exposure. After the water exposure test has been completed – within one hour of removal from the water – the compression test shall be repeated.
Flame Spread Test. ASTM E84 is a commonly used flame spread test. ASTM 2925 provides for its use as an option for those situations when specifying flame spread characteristics is necessary.
Freeze-Thaw (Optional). Maintaining physical characteristics while undergoing multiple freeze-thaw cycles is critical in many structures. Also, this test offers another means to assess parameter stability in simulated use situations. After the freeze-thaw exposure test has been completed – within one hour of the completion of the test – the compression test shall be repeated.
The use of ASTM E2925 to specify the various polymeric materials used in brick veneer and adhered masonry applications is an easy, effective means for specifiers and installers to insure that high-quality materials are installed. These materials perform the critical drainage and ventilation functions that help protect structures from moisture damage over the life cycle of the building. Additionally, the use of drainage materials is increasingly common behind other claddings.
For testing and performance specification details, the latest version of ASTM E2925 is available at ASTM.org.