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Waterproofing Challenges

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Waterproofing failures are more easily overlooked than roofing failures, but compared with a reroofing project, a below-grade or interior waterproofing rehabilitation can be far more disruptive and expensive. While prevention is the obvious first choice for waterproofing success, there are many occasions for error in design during construction and throughout operation. Richard P. Kadlubowski, AIA, Senior Vice President and Director of Architecture, Hoffmann Architects, Washington DC, USA elucidates.

Whereas a roof leak can generally be identified with simple test probes, w a t e r p r o o f i n g breaches can be challenging to diagnose. Even a seemingly superficial leak can be symptomatic of hidden moisturerelated deterioration. Water infiltration doesn’t fix itself. While it can be a major undertaking to properly identify and correct faulty waterproofing, it is far worse to adopt a patch-it-and hope-forthe-best attitude. All too often, even well-meaning attempts at treating the symptoms of waterproofing failure serve only to trap or redirect moisture, compounding the problem. Until the waterproofing deficiency is resolved, the problem will only get worse.

Waterproofing 101

Waterproofing 101 Various components contribute to a waterproofing system, such as drainage composites that direct water away from the structure, tieins between facade and foundation membranes, and watertight plumbing in food service areas. Impervious membranes are one critical component of waterproofing, both for below-grade applications, such as foundation walls, basements, tunnels and vaults and for areas subject to high moisture levels, like fountains, lobbies, kitchens and mechanical rooms. Waterproofing membranes may be applied in one of two ways: positive side and negative side.

Positive Side: By creating a waterproof barrier on the side of applied hydrostatic pressure, positive side waterproofing prevents water from entering the wall. For a foundation, this would be the outside surface, closest to the soil. For a fountain, it would be the inside, where the water is. For belowgrade
applications, the earth can be banked back such that a positive side membrane is installed after the foundation is set. In urban areas where every square inch comes at a premium, this may not be an option. Blind side waterproofing incorporates the waterproof membrane on the face of the shoring before the foundation is cast. Concrete is then poured, and the waterproofing fuses to the foundation wall as it cures.

Pros: Positive side systems, used both above and below-grade are generally preferred over negative side applications for their effectiveness. The structural barrier is completely protected from corrosive chemicals in groundwater as well as freeze-thaw cycle damage. Options include:

  • Fluid applied membranes, similar to those used in roofing applications, roll or brush on as a liquid and cure to form a monolithic, seamless membrane.
  • Sheet systems are also similar to those used on roofs, including single-ply thermoplastics and rubberized asphalts.
  • Hybrid systems combine a fluid-applied membrane with embedded fabric reinforcing to create a stronger, more resilient waterproof barrier.
  • Bentonite clay is a natural mineral derived from volcanic ash, which swells in the presence of moisture to create a solid clay barrier. It is applied as a sheet, mat, panel, or spray.

Waterproofing, because it is so difficult to access, should have a design life as long as that of the building. With so many opportunities for damage, incorrect design or poor execution, waterproofing systems can fail well before their time. When this happens, architectural investigation is needed to determine the location and cause of the leak, the extent of the damage and the appropriate remedy.

Cons: The shortcoming to positive side systems lies in leak detection and remediation. Blind side waterproofing cannot be inspected once the concrete is poured. Even for membranes installed after concrete is cast, it’s too late to correct for sloppy installation once the waterproofing is buried. If the system fails, rehabilitation can involve major excavation and reconstruction of paving, landscaping, and wall systems.

Negative side: Negative side waterproofing protects the surface opposite the side of applied hydrostatic pressure (the inside of a basement wall, for example) such that water is redirected after it enters the substrate.

Pros: Because the negative side is more accessible, it is easier to identify leak locations. Negative side coatings or injections also can be applied as a retrofit measure. Material types include:

  • Cementitious systems combine chemical waterproofing additives or acrylics with cement and sand to achieve an impervious surface.
  • Acrylic, latex, or crystalline additives are also available which penetrate into the surface to provide water protection.

Cons: Moisture does enter the wall system which can cause components to degrade over time. The constant presence of moisture can lead to mold growth, corrosion, concrete deterioration, or damage to interrelated building elements like floors or windows if not directed to escape the building system.

Combination systems: F o r sensitive spaces below-grade, more sophisticated systems have been used. As an example, a rare book vault built below the water table employed a wall-within-a-wall arrangement, with a pump system in the channel between the inner and outer walls to augment the positive side membrane.

Damp-proofing is not a substitute for waterproofing

Damp-proofing is a bitumen based or cementitious treatment applied to the positive side of foundation walls. The quick, inexpensive coating aims to discourage moisture from wicking up into below-grade walls through capillary action. Named for the tiny, thin apertures or capillaries, in porous materials like masonry and concrete, capillary action moves water from damp to dry areas, sometimes against gravity.

Waterproofing represents a much broader class of moisture protection. Unlike damp-proofing, which cannot bridge cracks, a waterproof membrane can stretch to accommodate some degree of differential movement, settlement, and shrinkage. Even when subjected to the hydrostatic pressure of a high concentration of water, waterproofing is designed to be flexible and durable.

Damp-proofing is sometimes used because it is much less expensive than a waterproof membrane. However, damp-proofing products are of a lesser grade than waterproofing materials, and they are applied as a sparse coat with little attention to detail. Waterproofing membranes demand precise application and detailing and they can be reinforced with integral fabrics for increased stability. True, damp-proof coatings are cheaper at the outset. But the long-term durability and effectiveness of properly selected and installed waterproofing are well worth the extra up-front cost.

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