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In this article, we will discuss several categories of concrete waterproofing products and describe their strengths and weaknesses.
Basements have a reputation of being dark, stuffy, and uncomfortable. So, it shouldn’t be a surprise that horror movies tend to mark basements as the birthplace of nightmares. Unfortunately, we cannot always avoid building down. In London, for instance, some homeowners are digging down to either create or extend basements to make living in London more affordable. If you have no choice but to make a livable basement, how do you solve its issues?
Some engineers have already developed unique solutions to bring in natural light to otherwise dark basements. Fortunately, creating a leakproof, comfortable basement does not have to be as complicated.
No one likes a wet, leaky basement
Wet, damp basements are not only uncomfortable, but also perfect incubators for mold and mildew. And a leaky basement is often a sign of a more serious problem such as compromised foundations. To get around this problem, builders typically employ a range of waterproofing techniques that rely on specialized products.
Waterproofing membrane products fall under four categories: fluid-applied systems, cementitious systems, sheet membrane systems, and bentonite clays. Fluid-applied systems are similar to applying coats of paint to the surface of the concrete. Cementitious systems are a way of describing concrete that has been combined with an active waterproofing agent. Sheet membrane systems involves adding a physical layer on top of the concrete in the form of a liner that provides waterproofing properties. Bentonite clay systems utilize a layer of water-absorbing clay (1).
The pros and cons of four waterproofing systems
Cementitious systems are not necessarily considered part of the category of concrete waterproofing products, but rather a waterproofing measure. With this approach, the water properties of the cement are augmented by combining a waterproofing agent to the cement mixture. While this approach is the simplest to implement, it is also the least reliable and should not be considered as a primary waterproofing measure. Instead, cementitious systems should be viewed as a secondary or backup waterproofing system.
While fluid-/spray-applied waterproofing coatings are typically the fastest, cheapest, and easiest solution to implement outside of the cementitious approach, they do come with a significant drawback. Fluid-applied systems are not particularly durable and the application can chip or wear away under certain conditions. Because the product can wear away, the lifetime cost of the product goes up when maintenance and repair costs are taken into consideration.
Sheet-membrane systems, or concrete protective liners, are made with thermoplastics, vulcanized rubbers, or rubberized asphalts. These systems are typically between 20 and 120 mils in thickness and offer more durability and strength compared with fluid-applied systems. Concrete protective liners do carry some drawbacks though. For instance, the sheets often need to be welded in the field, which can slow down installation. Also, it can be difficult to locate the source of leaks as the moisture can migrate away from the leak site. However, the use of waterstop profiles can minimize this issue by compartmentalizing smaller areas which can be grouted if a leak is detected.
Bentonite Clay Systems
Composite sodium bentonite systems incorporate water absorbent clay as a waterproofing layer. While highly effective as a waterproofing layer since the clay can absorb moisture, it can be difficult to properly install on its own as unconfined clay can expand and shrink over time, leading to gaps that allow for moisture to enter. Therefore, bentonite clay systems are typically built in conjunction with HDPE liners and geotextile fabrics, using the HDPE liner as the primary waterproofing membrane with a layer of bentonite confined with geotextile.
- 1. Postma, “Foundation Walls.” WBDG. (2016). Accessed online 2 December 2019. https://www.wbdg.org/guides-specifications/building-envelope-design-guide/below-grade-systems/foundation-walls.