Understanding sealants and flashings for masonry

by Elaina Adams | December 1, 2012 2:45 pm

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By Steven Fechino
An important part of many Canadian project teams, the masonry industry is a proud group that builds durable structures using time-honoured techniques that have spanned generations. Discipline and mentoring are the keys to learning the ‘laws’ that make up this complex trade. As with all things, masonry has rules that will and will not change over time:

1. Masons get paid for what they lay on the wall, not for effort.
2. Completing a job correctly costs the mason four times less than a mistake (i.e. once for removal of defective work, twice for its replacement, three and four times for the jobs not completed while the repair work was performed).
3. A wall without flashing, completed properly, has a 95 per cent chance of leaking, as opposed to one flashed correctly, which is almost
   zero per cent.

Masonry contractors across the country know these three rules, as do many of the architects, specifiers, engineers, and building owners who work closely with them. However, some of the other long-lasting rules have recently undergone some changes.

For example, sealants and flashing technology have improved over the last few years. Products designed to improve the workmanship and quality over what has been available in the past are now available for residential and commercial masonry contractors. With many other recent innovations, new flashing fabrics, membranes, and composites have been created to give the masonry and roofing contractor better options to serve their building owners.

Sealants
Early in this author’s career, before sealants had evolved into what they are now, bituminous mastics were commonly employed to lap flashings, patch around dowels, and seal penetrations that passed through the wall. Bituminous mastics, when used now, should be checked for compatibility with today’s flashings. When determining the compatibility between products, one can simply call the manufacturer and ask; it is also a good idea to request a letter stating the approval or disapproval of the product.

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Butyl
Butyl has had a long run in the construction industry, primarily due to the adaptability of the product to the roofing sector. This synthetic rubber, available in sealant tube form as well as tape rolls, is typically more economical to use in the correct application than some of the other sealants on the market.

When making a flashing lap or sealing around dowels, butyl can be an ideal choice. However, it cannot be used for general joint-sealing, expansion joints, or any exposed joints, as this material remains uncured and loose for the life of the product. Butyl is compatible with products made with current formulations of:

• polyvinyl chloride (PVC);
• thermoplastic polyolefin (TPO);
• ethylene propylene diene monomer (EPDM);
• laminated copper fabrics; and
• most rubberized asphalts.

Polyurethanes
Polyurethanes tend to be the most commonly used and accepted sealants for sealing masonry-to-masonry, masonry-to-dissimilar material, and flashing laps. These products are typically one-or-two part sealants that offer a wide range of colours for construction-related joint-sealing.

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Polyurethanes offer a lifespan ranging from six to 10 years, depending on exposure and geographical location. The working temperatures of polyurethanes are limited from 4 to 35 C (40 to 95 F), with a typical tack-free time of four hours. Single-part polyurethanes are often moisture-cured, while two-part sealants are chemically cured.

Modified polyethers
Modified polyethers have become a new force in the sealant industry. Polyethers are modified silicones that have the gunnability (i.e. flowability out of a caulking gun) of silicone and the most desirable characteristics of polyurethanes. They do not migrate oils into porous masonry and are gunnable in temperatures down to –9 C (15 F).

Given their low level of volatile organic compounds (VOCs) and quick tack-free time (depending on temperature and humidity, usually about an hour), polyethers are expected to eventually replace the popularity of polyurethanes. The chemistry exhibits superior joint material performance and bonding to various membranes and substrates. The material can also be installed in a range of weather conditions. Polyether used with a primer will seal TPO products with excellent results. In terms of first costs, polyethers are a bit higher than polyurethanes, but they have a longer life. Polyurethanes remain suitable for masonry, but are not typically good enough to bond to most new flashing materials.

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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.

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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.

For more on Sealants and flashings for masonry, click here[6].

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