Uncovering the unseen: Blindside waterproofing

by tanya_martins_2 | December 7, 2024 2:44 pm

By Rockford Boyer, B. Arch. Sc., MBSc, BSS

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In the construction industry, much attention is given to the visible and esthetically pleasing aspects of buildings. These elements often win awards and gain recognition, while the hidden components that do not catch the eye are frequently overlooked. However, this focus on the visible can have serious implications, especially regarding critical building systems such as below-grade waterproofing, building enclosures, and low-sloped roofing.

These systems are often overshadowed by visually appealing architectural elements, such as cladding, building entrances, and interior finishes. This phenomenon can be described as the “blindside” of construction: the tendency to ignore what is hidden below the surface. Unfortunately, the consequences of neglecting these unseen components can be devastating, leading to costly failures that are difficult to address.

This industry-wide mindset needs to shift. Decisions in construction should no longer be based solely on cost but on performance. While cost is undoubtedly an essential factor, it is equally important to educate building owners about the long-term implications of their choices—especially when it comes to systems such as waterproofing, which are designed to protect the integrity of the entire structure. The goal should be to prioritize durability and long-term performance, ensuring the unseen elements of a building are just as reliable as the visible ones.

The need for better education in construction

Education is the key to making this shift happen. While innovation in the construction industry may seem slow at times, manufacturers are constantly working behind the scenes to develop new products and solutions that address the challenges of modern building projects, tie together new products and solutions with old products, and present the chemistries used in new ways. These innovations are often the result of collaboration between designers, engineers, and contractors who identify gaps in existing solutions and work together to create better alternatives.

However, these new materials and systems often do not fit established standards or traditional construction practices. This is where the importance of on-site mockups and trials comes into play. By demonstrating the performance of these new products in a real-world setting, design teams can fully understand how they will work in practice. This collaborative approach helps to ensure all parties involved in the project are on the same page and the chosen solution will meet the expectations of the design team, contractors, and building owners. After final product characteristics are decided upon, the manufacturer works with third-party testing labs and the government to ensure product quality and predicted performance.

One innovative material that has recently gained traction in the Canadian commercial and residential waterproofing markets is polyurea. Although this material has been used in various industries for decades, its potential in below-grade waterproofing was not fully realized until it was needed to address material and labour shortages caused by the global pandemic. The increased demand for durable, reliable, and easily applied waterproofing solutions highlighted the benefits of polyurea, bringing it into the spotlight as a viable solution for designers and contractors alike.

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The forgotten foundation: Why blindside waterproofing matters

When considering the most overlooked parts of any building, one needs to turn their attention underground. The foundation, basement, or below-grade components are often forgotten because they are hidden from view and buried deep beneath the surface. Unfortunately, this “out of sight, out of mind” mentality can lead to severe problems—particularly when it comes to waterproofing.

Below-grade waterproofing is critical for protecting a building from water infiltration, yet it is frequently neglected. This neglect is often driven by a desire to minimize costs, leading to inferior materials or rushed installations. In some cases, builders adopt a “set it and forget it” approach, assuming that once the waterproofing system is in place, it will function as intended without further thought. However, this approach can lead to catastrophic failures—especially when a blindside waterproofing system is involved.

Blindside waterproofing refers to systems installed below grade where excavation beyond the outer foundation wall is not possible. This might be due to neighbouring structures, zero-lot lines, or important infrastructure. Unlike traditional waterproofing, which is applied after the foundation wall is built, blindside waterproofing is installed before the foundation is poured, making it particularly challenging to repair once the concrete is in place.

When a blindside waterproofing system fails, the results can be disastrous. Since the waterproofing layer is behind the concrete foundation, repairs are nearly impossible without significant disruption and expense. This makes it crucial to ensure the system is installed correctly from the outset, with careful attention to detail at every step of the process.

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Leaks in below-grade commercial foundations, such as parking garages, are a common sign of waterproofing failures. In some cases, the evidence of these failures is visible through crack repairs or the installation of water pumps to manage excessive water flow. These issues underscore the importance of high-quality waterproofing solutions and proper installation practices. Failing to address these critical systems during construction can lead to costly repairs and ongoing maintenance headaches.

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Understanding blindside waterproofing: Components and application

Blindside waterproofing systems are designed to protect below-grade structures from water infiltration when excavation beyond the foundation wall is not feasible. These systems are commonly used in urban environments where neighbouring buildings, streets, or underground infrastructure prevent traditional excavation techniques.

Blindside waterproofing systems consist of several key components, each of which plays a critical role in protecting the foundation from water:

Soil retention system

The first component of any blindside waterproofing system is the soil retention system. This system is responsible for holding back the earth during excavation, allowing the construction team to work safely. Several common soil retention systems are used in Canada, including steel soldier piles with wood lagging, soil nailing, and shotcrete. In some cases, additional support elements such as rakers and walers ensure the soil retention system remains structurally sound. These elements often stay in place during waterproofing, requiring careful co-ordination to apply the membrane around them continuously.

Drainage mat

The next component is the drainage mat, typically a two-layer dimpled polypropylene membrane with an attached filter fabric. This mat is fastened directly to the soil retention system and serves two critical functions. First, it allows water to drain away from the foundation, preventing it from building up against the waterproofing membrane. Second, it provides a surface to which the waterproofing membrane can adhere. The drainage mat is typically blocked at grade to minimize the amount of bulk water entering the drainage space.

Waterproofing membrane

The waterproofing membrane is the most critical component of the blindside waterproofing system. Its role is to create a continuous, durable barrier that prevents water from reaching the foundation. Several waterproofing membranes are available, including sheet membranes (such as asphaltic or bentonite) and liquid-applied membranes. Liquid-applied membranes, such as polyurea, are particularly well-suited to blindside applications because they can be applied seamlessly to create a monolithic waterproofing barrier.

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Structural wall

The final component is the structural wall itself. This is typically reinforced concrete and provides the foundation for the entire building. Since concrete is prone to cracking and shrinking over time, it is essential to ensure the waterproofing membrane behind it is continuous and well-installed. Once the concrete is in place, repairing the waterproofing system is extremely difficult, if not impossible. While crack injection repairs can be performed after the fact, they are often temporary and may fail over time.

Innovations in blindside waterproofing

In recent years, several innovations have emerged in blindside waterproofing. These advancements have been partly driven by the challenges posed by the COVID-19 pandemic, which led to material shortages and supply chain disruptions. One of the most significant innovations is the increased use of polyurea. This liquid-applied waterproofing material has been used in Canada for decades but has only recently gained traction in below-grade applications.

Polyurea was initially developed in the 1980s as a replacement for polyurethane coatings, which were more susceptible to moisture during application. It has been used in many applications, including waterproofing for holding tanks, underground tunnels, reservoirs, and automotive manufacturing. Polyurea’s fast curing time, durability, and resistance to abrasion and corrosion make it an ideal solution for waterproofing below-grade structures. In the past few years, polyurea combined with high-density sprayfoam waterproofing has been successfully utilized in below-grade applications from Newfoundland to British Columbia and everywhere in between.

One of the critical advantages of polyurea is its quick application process. The material is created by mixing two raw materials at high pressure through a plural component spray system and applying them to a surface. Once the material reaches the surface, the cure time for the polyurea is about 20 seconds and will be dry/tacky to the touch. The typical application thickness can vary from 50- to 200-mil and will depend on the orientation and the application requirements. The recommended substrates for the vertical application of polyurea waterproofing are high-density (HD) closed-cell sprayed polyurethane foam (ccSPF) or a drainage membrane with fabric on both faces of the membrane. Other substrates can be used; however, it is always good construction practice to verify substrates and primer use with the manufacturer before application of the waterproofing membrane.

Polyurea is quickly gaining traction in commercial construction due to its fast-curing properties, its resistance to abrasion and corrosion, and how it allows construction teams to move on to the project’s next phase quickly—reducing downtime and minimizing the risk of delays. If the polyurea is to be exposed, it can also have additives mixed in with the resin to resist the damaging impacts of UV light. The best way to visualize this polyurea waterproofing product is to think of a truck bed liner coating, as these products have similar performance characteristics.

Another significant innovation in blindside waterproofing is the development of advanced drainage systems. Manufacturers have introduced new drainage boards that facilitate drainage and serve as carriers for liquid-applied membranes.

These drainage boards consist of a 3D drainage composite board manufactured from high-strength polypropylene, which can resist more than 55,158 kPa (8,000 psi). A geotextile is heat bonded to both the dimple side and the back side of the drainage board to prevent clogging from infiltrating soil on the excavated side, and the geotextile on the back side allows for a suitable substrate for both a sprayed polyurethane foam and/or a polyurea waterproofing membrane. The drainage board is typically fastened directly to the substrate (dimples inward) with mechanical fastening secured through the substrate. A geotextile “flap” or overhang is present on one of the back sides of the drainage board to allow for a seamless waterproofing application at the seams of the installed drainage board. The drainage board must be continuously installed to allow for unimpeded drainage from the excavated side down to a location at the base of the wall where it can be properly drained or removed from the site.

In addition to advancements in waterproofing membranes and drainage systems, there has also been a recent trend toward insulating foundation walls with spray-applied insulation before the concrete is poured. This insulation helps regulate below-grade temperatures and provides a secondary layer of protection against water infiltration. To meet the demands of below-grade applications, manufacturers have developed high-compression ccSPF structural foam that can withstand heavy loads and resist mechanical damage.

One key challenge with below-grade insulation is ensuring it can handle the extreme pressures exerted by the surrounding soil and the building above. High-compression ccSPF has been designed to meet this challenge, offering compression resistance of up to 689 kPa (100 psi). At the same time, environmental concerns have led to the elimination of harmful blowing agents from the manufacturing process, reducing the environmental impact of these products.

While high-compression ccSPF has a slightly lower RSI value than traditional sprayfoam insulation, this is not a significant concern in below-grade applications. The lower the temperature differential, the deeper the foundation becomes, meaning the reduced RSI value has little impact on the overall performance of the insulation. As for the sequencing, the ccSPF can be applied directly to the double-faced drainage board with the waterproofing overtop, or it can be reversed with the waterproofing applied to the drainage board and the high-compression ccSPF installed overtop.

Successful application of a blindside waterproofing system

To further illustrate the importance of blindside waterproofing and the effectiveness of modern innovations, here is an example of how these products can work together. Consider a large-scale commercial development in Toronto. The project involves constructing a multilevel underground parking garage beneath a high-rise office building. Due to the tight urban setting, traditional excavation methods are not feasible, so blindside waterproofing is required.

The construction team decides to use a combination of polyurea waterproofing and high-compression ccSPF insulation to protect the foundation from water intrusion. The polyurea is applied directly to a double-sided drainage board, creating a continuous waterproofing layer that can withstand the pressures of the surrounding soil. The drainage board also facilitates water flow away from the foundation, minimizing the risk of water buildup.

The use of polyurea in this scenario is a game-changer for the project. Its fast-curing time allows the construction team to stay on schedule despite a tight timeline, while its resilience and durability ensure long-term protection for the foundation. The ccSPF structural foam insulation provides compressive strength and additional protection against water, making the entire system more robust and efficient. This exemplifies how these three innovative products can build a long-lasting and high-performing foundation.

Conclusion

Blindside waterproofing may not be the most glamorous aspect of building construction, but it is one of the most important. Systems such as below-grade waterproofing, building enclosures, and low-sloped roofing play a critical role in ensuring a structure’s long-term performance and durability. Yet, these systems are often neglected in favour of more visible, esthetically pleasing features.

It is time for the construction industry to shift its focus from cost to performance. By prioritizing high-quality materials and innovative solutions such as polyurea waterproofing, advanced drainage systems, and high-compression ccSPF insulation, design teams can ensure buildings are visually appealing, structurally sound, and built to last.

Education and collaboration among designers, engineers, and contractors are essential to this shift. By working together and sharing knowledge about the latest innovations in blindside waterproofing, they can prevent costly failures and create buildings that stand the test of time. Ultimately, it is about more than just appearances—it is about building structures that are as strong, resilient, and beautiful.

Author

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Rockford Boyer, B. Arch. Sc., MBSc, BSS, is an experienced building science leader at Elastochem with more than 20 years of expertise in sustainable building design. He holds an undergraduate degree in civil engineering and architecture and a master’s in building science. He is also a member of Passive House Canada and the Ontario Building Envelope Council (OBEC). He is also a part-time professor at Sheridan College, teaching in the architectural technology program and sharing his knowledge and expertise with future generations of architects and designers.

Source URL: https://www.constructioncanada.net/uncovering-the-unseen-blindside-waterproofing/

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