Don’t Put All your Eggs in One Waterproof Basket

by John Chamberlin, MBA

This photo shows above-grade moisture protection with coating over joint treatment and rough opening protection. Photos courtesy Sto Corp.

“A building is only as strong as its foundation,” is a common idiom uttered across the construction industry. Time can be spent applying this to anything, in the metaphorical sense, but in the construction business it can be taken literally. The foundation is literally the building block on which the rest of a building will rely for long-term function and performance.

Foundations—and more specifically, their below-grade waterproofing systems—need to be resistant to hydrostatic pressure. These should be able to adapt to structural movement, and should include some means of enhanced drainage. However, it is important to remember these systems are generally going to be buried. This means they need to be able to retain their performance characteristics years after they have been installed, even though they will basically be completely inaccessible within a short time of being installed.

This can sound like a lot of pressure (pun intended) to put on a product or system. However, many design professionals have a solution in which they trust and feel confident, and cite above-grade waterproofing as a bigger challenge. What is it that makes above-grade waterproofing such a complex decision?

First, modern walls are relatively thin—in most cases they can be measured in inches. A lot of the time these walls are being built with materials susceptible to moisture intrusion—such as wood-based sheathings and highly porous claddings—so a waterproofing product needs to be moisture-resistant whether it is a standalone solution or a component within a system.

Further, moisture has a handful of ways it makes its way of penetrating the building envelope. As a result, waterproofing needs to account for differentials in air pressure, wind loads, capillary action, and surface tension for design professionals, this means waterproofing components should be non-absorptive, durable, and be able to work on their own or as part of a system to act as an air and moisture barrier.

Additionally, a building should be able to ‘breathe,’ so above-grade waterproofing should stop water in liquid form from getting in, while still allowing water in vapor form to move out from inside the wall. Waterproofing continuity is a must throughout the building’s lifetime. Unfortunately, buildings do not remain still. Similar to below-grade waterproofing, above-grade waterproofing must account for structural movement, dealing with the building’s constant expansion and contraction caused by temperature fluctuations and thermal movement.

With these various performance characteristics to consider, buildings should still be esthetically pleasing. Generally, owners will not be happy with a completely waterproofed building that is also unbelievably ugly. Therefore, above-grade waterproofing needs to allow for design flexibility as well to add curb appeal to the building. With all these different demands on a product or a system, how is a designer supposed to come up with the ideal solution?

This pipe penetration is being treated with a liquid-applied moisture barrier.

Many design professionals subscribe to the three Ds of design: deflect, drain, and dry. Keeping these considerations in mind, some of the ways an above-grade waterproofing system can come together are visible. The first place to look for an opportunity to stop, or deflect, moisture is on the cladding itself. A quick look at modern stucco and exterior insulation and finishing system (EIFS) systems shows acrylic finishes are available, offering a high degree of moisture resistance, even going so far as to create super-hydrophobic surfaces, while still offering a wide range of esthetically pleasing design options.

To go even further, these systems generally include back-up assemblies, adding redundant means of drainage and drying for long-term and high-performing protection against damage caused by moisture intrusion in the event of a breach in the outer EIFS surface. Protective functional coatings and clear-coat sealers are another means of deflecting moisture on the surface of the cladding while still creating an attractive façade.

However, finishes, coatings, and clear sealers are not ideal for all claddings. For example, brick might be more attractive when left natural. In that case, waterproofing should take place behind the cladding, protecting the wall substrate, joints, and penetrations, as well as including a system of flashings, weeps, and other accessories to help moisture drain from inside and allow air movement to more quickly dry the wall. Traditional means of waterproofing behind the cladding include wrap-type products or self-adhered membranes. These can be high-performance products, but may provide challenges in terms of application and long-term performance.

More recently, fluid-applied air and moisture barriers have come onto the market, offering ease of application and long-term durability, as well as the same performance characteristics as the more traditional solutions. Regardless of which method is chosen, the devil is in the details.

A well-thought-out system will include detailing at rough openings, penetrations, and static, as well as movement joints all seamlessly integrated into the protection on the field of the wall. These details will often be the difference between a high-performance wall and one that leaks.

Above-grade waterproofing is a necessity for any building intended to remain standing longer than a couple years. While the ideal method might not be the easiest decision, design professionals should be comforted by the fact so many options are available to them, not only to provide long-term performance and function, but also to allow them to create a building with great curb appeal. So many considerations for above-grade waterproofing should be seen as an opportunity for design professionals to identify a system that will offer the best possible combination of performance and aesthetics.

John ChamberlinJohn Chamberlin, MBA, is product manager for StoGuard and StoEnergy Guard at Sto Corp. His divisions are focused on heat, air, and moisture management within the building envelope. Prior to this position, Chamberlin served as product manager for StoCoatings, and was also associate product manager for StoPowerwall and StoQuik Silver. Chamberlain earned his MBA from Emory University and is a graduate of the University of Tennessee, with a bachelor’s of science in marketing. He can be contacted by e-mail at jchamberlin@stocorp.com.

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