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.






LathNet detail drawing

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

lathnet-with-code-overlapAdhered masonry veneer can be installed using five different building techniques

An adhered masonry veneer is a cost-effective way for a home owner or commercial property owner to keep the appearance of masonry in the façade, even when budgets or design considerations don’t allow the use of full-sized masonry units. However, veneer installation is based on recommendations of the specific product and system chosen for your project. With that in mind, here’s a breakdown of basic installation using five standard building techniques that can help you in your next project.


  1. Weep Screed

The purpose of the weep screed is to provide drainage for the system. It typically is a galvanized metal or a durable plastic strip placed at the base of the wall and, in some cases, at each floor level of a large veneer. The galvanized weep screed must be at least 26 gauge (0.018 inches) thick. The plastic weep screed must be a minimum thickness of 0.05 inch, and both products must extend up the wall a minimum of 3.5 inches. They both must also be fastened to a stud in frame construction, or directly to the concrete or concrete masonry unit (CMU) substrate.

To function properly, weep screeds should be a minimum of four inches above grade and two inches above a roof line. If applying veneer to a CMU or cast-in-place grade or foundation wall, the minimum tolerance is two inches from a sidewalk or driveway surface. This placement will reduce the possibility of the weeps becoming clogged with debris that splashes on the wall. Attach your weep screed prior to placing the weather resistant barrier (WRB) on your project, since it is easier to install the overlap when the weep screed is in place. Many building code officials have become more rigid on the enforcement of these standards in recent years.

  1. Weather Resistant Barrier (WRB)

The WRB sheds the moisture that passes through the veneer away from the substrate and allows drainage to the weep screed or flashings. Two individual layers of house wrap or building felt sealed with tape surrounding the structure typically are required. When a drainage mat is used directly against the lath as part of the wall system, one layer of WRB is eliminated (check local codes). When a drainage mat is used, air and moisture can move with significantly less resistance behind the veneer, and the wall is usually dryer than one without a drainage mat. The WRB is installed after the weep screed is in place, and must drape over the weep screed to allow moisture to be channeled past the face of the wall.

  1. Continuous Insulation

Continuous insulation, or rigid insulation, has become increasingly popular, and the installation of adhered masonry veneers on the exterior side of the insulation is allowed as a non-engineered system for insulation that is a thickness of ½ inch or less. Designs using insulation greater than ½ inch in thickness require an engineered anchoring system. Specialty washers for anchoring lath over rigid insulation are available where you purchase your insulation or from the rigid insulation manufacturers. There are several options, and the manufacturers can guide easily you in the right direction when specifying or constructing a project with the thicker insulation.

Continuous insulation, when placed as the outermost layer on the structure prior to lath installation, can eliminate the need for a second layer of WRB. The inner layer of WRB must have all of the joints sealed and taped for the system to work properly.

  1. Fasteners

Adhered masonry veneers can be applied to concrete, CMU, steel stud and wood stud substrates. The allowable non-corrosive or corrosion-resistant anchors used for anchoring lath or lath systems are as follows:

Wood frame: Staples, roofing nails and screws can be used. The minimum embedment is ¾ inch, but a minimum of one inch is a good practice to follow.

Steel stud: The only anchor recommended for steel stud is the self-tapping screw or hex head anchor with a neoprene washer attached to the anchor. Minimum embedment is 3/8 inch, but again, a greater depth will increase your odds of success.

Concrete or concrete masonry units: Powder actuated fasteners, also known as cap anchors, are allowable for this installation. Powder actuated anchors do not need pilot holes, but are not used commonly. Concrete masonry screws are a good choice as they can be monitored for embedment; will not blow through the substrate; and typically are more economical.

Innovations in lath during the last several years have opened the market to different ideas, when thinking about the lath that is integral to adhered masonry systems.

  1. Metal Lath

Metal Lath is manufactured by several outstanding domestic manufacturers. Metal lath used today is a galvanized, self-furring, dimpled product that allows the lath to project ¼ inch out from the substrate, so the base or scratch coat mortar can fully encapsulate the lath. Lath weight is expressed in pounds per square yard, and is offered in three different weights: 1.75 pounds, 2.5 pounds and 3.4 pounds. The most common is 2.5, but, in some areas, all of the specifications are written for 3.4 material.

Lath placement or orientation is no longer stipulated by local codes. It is still most productive to install lath horizontally – one over two for example – and the days of “cups up, smooth down” have been eliminated. Do not terminate lath at a corner. Always extend the lath past an outside corner a minimum of 12 inches. Lath can be terminated at an inside corner. Anchor lath a minimum of every seven inches vertically, and at every stud, or 16 inches on center.