Understanding sealants and flashings for masonry

Various proprietary unitized flashing systems can include membranes, pre-designed laps, screws, weeps, termination bars, drip edges, and mortar-collection devices.
Various proprietary unitized flashing systems can include membranes, pre-designed laps, screws, weeps, termination bars, drip edges, and mortar-collection devices.

Flashings
Flashings have seen the biggest change in the market over the past few years, with the roofing industry introducing products that have proved their long-term value.

Copper laminate
The tried and true copper laminate material with which all design/construction professionals are familiar is still on the market. However, some companies have made proprietary tweaks. For example, products have been made more durable by laminating a mesh of polyethylene on both sides of the copper. Nearly impossible to cut with a trowel, this premium flashing material is intended to perform well for years.

Rubberized asphalt
Rubberized asphalt is the most common flashing on the market today, with several companies breaking up the geography of North America. The commonly installed rubberized asphalt (i.e. sticky-back) material is stable when properly installed. Primers are sold by some manufacturers as part of every application, and other companies omit the primer when the project team uses a term bar. It is critical the masonry contractor and designer read the fine print for each product as warranties can depend on the use of primers.

Compatibility between rubberized asphalt and PVC moulded corner boots and end-dams should be investigated before construction as plasticizers can migrate from the PVC and reduce the plasticity of the rubberized asphalt over time, causing the potential for a leak down the road.

PVC
Polyvinyl chloride flashings are not the flashings of the 1980s—they should not carry any of the reputation of the first-generation PVCs that entered the market. Modern materials combine old and new technology to create strong, durable, and flexible components thanks to the addition of non-migratory plasticizers. In other words, the stabilizing ingredient will not leach out of the plastic, evaporate, or allow the PVC to break down and become brittle (which would otherwise enable cracks and leaks).

PVC is as good a membrane as any on the market. A crossover from the roofing industry, it is also compatible with many polyurethanes, polyethers, and butyls.

TPO
TPO is another product mason contractors inherited from the roofing industry. Thermoplastic polyolefin is a flexible membrane that has a 30-year lifespan when installed on a roof, and a virtually unlimited one when placed in the building’s cavity. TPO has an advantage over all other membranes on the market because it can seal the laps using a butyl sealant or
primed polyether.

One can also hot-air-weld (i.e. heat-weld) them to provide a joint completely bonded by hot air. This author heat-welded a 0.6-m (2-ft) TPO section in about a minute, and water-tested it several minutes later with positive results—no leaks. Low-cost equipment for heat-welding can be purchased for under $100 and would reduce the sealant requirements for installing flashing by a 15.6 to 320-g (½ to 10.3-oz) tube per lap. Unprimed polyethers and polyurethanes cannot be used for sealing this membrane, as its surface energy will not allow a durable long-term bond.

EPDM
EPDM is another roofing crossover material that has entered the masonry industry over the past several years. EPDM is flexible and easy to cut, and will quickly install as it has little memory to the roll in hot or cold temperatures. EPDM is a rubber that responds well to certain polyethers and butyls as a lap sealant and general installation sealant. It is incompatible with PVC moulded corner boots or end-dams. EPDM must have similar components for terminations and corners applications, and it is compatible with most air barriers on the market.

For the barracks, inspections revealed the flashing failed in numerous locations, particularly at transitions. The result was moisture could move laterally, necessitating replacement work.
For the barracks, inspections revealed the flashing failed in numerous locations, particularly at transitions. The result was moisture could move laterally, necessitating replacement work.

Unitized
Unitized flashings are single-component flashing systems that can be offered with any of the different flashing membranes that have been discussed in this article. Inclusions to the system can consist of a membrane, pre-designed laps, screws, weeps, termination bar, drip edge, and proprietary mortar-collection devices (that should pass the requirements of ASTM E514, Standard Test Method for Water Penetration and Leakage Through Masonry).

Unitized flashing solutions can also come with manufacturer-supplied pre-engineered flashing take-offs, and special cut panels for window and door heads delivered to the jobsite. These types of products can carry a premium cost, but the economic benefits have been proven over the years with virtually no failures reported.

Roll flashing
Another newer option involves roll flashing, which are assemblies that have the mortar-collection system attached directly to the membrane. With clean lap spaces available every 152 mm (6 in.) and weeps built into the roll, these products have the flexibility to rely on any of the aforementioned membranes and composites.

All the flashing membranes mentioned in this article are compatible with the various high-loft non-woven and unilateral mesh products used in mortar-collection devices and mesh wall fabrics that cover the entire inner wythe of the structure. However, it is critical the wall mesh not be placed behind the termination bar. Placement of the mesh should extend over the termination bar and lap about 25 mm (1 in.) over the flashing.

Conclusion
The last major improvement observed in the sealant and flashing market is that masonry contractors and specifying architects can more easily obtain answers to technical questions than even a few years ago. Many of the flashing manufacturers have created in-house specialized staff to serve as consultants on the various proprietary materials.

As with any industry, parts of the masonry flashing and sealant industry are constantly changing the rules for the benefit of the design/construction team. The goal is to improve projects by preventing one leak at a time.

Steven Fechino is engineering and construction manager at Mortar Net USA Ltd. He has more than 30 years of experience in the masonry and engineering field. Fechino frequently contributes to masonry and technical publications and websites, and is a subject matter expert for the U.S. National Center for Construction Education and Research (NCCER). He can be contacted via e-mail at sfechino@mortarnet.com.

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