December 1, 2012
By Russell Snow, CSP, CTR, BSSO, LEED AP
Moisture infiltration can cause serious damage within a structure. When water in liquid form is present, the impact can be catastrophic—the structure can become uninhabitable. There are various methods used to address water penetration within a structure, and two of the most common techniques are waterproofing and dampproofing.
Both these options can prevent moisture, but waterproofing will resist the passage of water under hydrostatic head pressure. In other words, it stops liquid water penetration when the water is in contact with the waterproofing material. In comparison, dampproofing only resists water in the absence of this hydrostatic pressure. To effectively protect against liquid water intrusion, waterproofing therefore constitutes an essential component in a structure’s long-term durability and performance, representing a key element in design and construction.
Several waterproofing products and systems are available in the marketplace, but it is a case of ‘specifier beware:’ there is no single system that will work for every situation. The critical issue in evaluating and specifying materials for any potential application is knowing all systems and technologies come with strengths and limitations.
As with any project, the role of the participants in the design and construction team is critical for waterproofing success; when considering such technologies for long-term performance, the team approach is a must. During design, the architect needs to consult the manufacturer to ensure the correct material is being selected and is being properly incorporated. During construction, it is essential the installer be fully trained in the application of the system, and is able to communicate any concerns that may arise during installation. Finally, on completion, inspection of the system can provide a level of assurance the waterproofing has been installed correctly and any potential issues have been addressed.
There are numerous critical factors that must be considered during the selection process of a waterproofing system; all of them should be addressed to ensure the correct system selected will perform for the environment in which it is being installed.
Local building codes set mandatory requirements for the structural safety of buildings and the designer needs to ensure the material is meeting or exceeding these requirements. The building codes typically provide the minimum requirements; a number of these waterproofing systems far exceed what is required.
Geotechnical reports will provide relevant information as to the groundwater conditions and should be reviewed as there can be seasonal variations affecting the elevation of the water table. This is extremely important to consider as one of the fundamental characteristics when selecting a waterproofing system is its resistance to hydrostatic pressure—that is, the material’s ability to withstand the pressure of the water exerted on it. (At greater depths, the hydrostatic pressure will increase.)
Chemical and physical properties of the soil can affect a waterproofing system’s long-term durability. For example, use of a negative-side (described later in this article) waterproofing membrane in an area with high soil pH can result in deterioration of the concrete and the reinforcement within the concrete. Also, when using a positive-side system (described later), it is important soil contaminants are not highly corrosive or able to damage or degrade the waterproofing system. An example here would be the use of rubberized asphalt membranes in an area contaminated with petroleum products.
When considering a system, it is critical to review the foundation and concrete slabs, along with the types of soils surrounding the structure. In areas where there is the potential for cracking of the substrate, it is often desirable to specify a flexible system with self-sealing characteristics.
Construction procedures and schedules
When considering procedures and schedules, several questions must be answered:
Product reliability and past performance
When considering waterproofing methods, it is important to look at both the material being considered and the manufacturer. Selecting a material that has a history of performing in similar situations is important and provides a level of comfort. Using materials from a reputable manufacturer with a successful track record will also go a long way in the selection process.
Air quality regulations
There are various rules and regulations that closely regulate the types of materials and their use. The advent of the volatile organic compound (VOC) regulation in Canada has dictated change in the types of solvent-based adhesives and primers being used. (For more on VOCs, see the article, “Understanding Canada’s VOC Regulations,” by Dianne Carey, CSI, CDT, in the July 2012 issue of Construction Canada. Visit www.constructioncanada.net and select “Archives.”) It is essential the designer review these before selection.
Waterproofing system placement
It should be determined whether the material is to be applied on the positive or negative side of the wall. Both of these present advantages and disadvantages and require specific systems to perform effectively. It is essential the selected system provide waterproofing, dampproofing, and capillary action, be continuous, and remain durable for the life of the structure.
Positive-side waterproofing systems are applied to the exterior of a structure, sometimes referred to as the ‘wet’ side; this is the predominant choice of waterproofing. Typically, this is the most effective type of waterproofing, as it not only protects the interior of the structure from moisture infiltration, but also blocks entry of moisture into the concrete substrate. Positive-side waterproofing, as a result, can protect against corrosion of reinforcing steel in the concrete or, in climates susceptible to freeze-thaw cycling, deterioration of the concrete. However, one of the limitations of this material is it can be difficult and costly to repair once installed. All types of commercially available waterproofing systems can be applied on the positive side of a wall.
When it comes to negative-side waterproofing, systems are applied to the interior surface, or ‘dry’ side of the concrete. It is essential negative-side waterproofing withstand hydrostatic pressure, but also possess some level of breathability (i.e. water-vapour permeability) to prevent problems due to entrapment of water vapour and capillary pressures in the substrate.
Non-breathable coatings—such as epoxies and urethanes—can delaminate from the surface due to vapour entrapment and movement. Proven systems used in this sort of application consist of crystalline materials or cementitious coatings. An advantage of negative-side waterproofing is these systems are ‘accessible’ when repairs are needed. A disadvantage is water penetrates into the substrate, resulting in potential issues with corrosion or freeze-thaw deterioration, as previously mentioned.
Once all these considerations have been addressed, it becomes time to review the actual materials and systems available. It is important to consider the type of approach to be followed and to select the specific system based on its performance requirements. Due to the sheer number of waterproofing technologies and systems, the focus of this summary review will be on some of the materials used commonly in design and construction below-grade applications.
Sheet membranes can consist of self-adhesive, thermofusible (i.e. torch-on) and certain blindside waterproofing membranes. A major advantage of sheet membranes is factory-controlled thickness, with no onsite fabrication required. Self-adhesive membranes are manufactured with styrene-butadiene-styrene (SBS)-modified bitumen, which provides excellent elongation and recovery characteristics.
Additionally, SBS modification of the membrane prevents ‘drying out’ by facilitating retention of bitumen oils. Application of these materials requires use of a primer before application to consolidate any laitance on the substrate. Application is relatively easy, with no special tools or equipment required.
Thermofusible membranes are also composed of SBS-modified bitumen, and require a propane torch to melt the backing and soften the bitumen. Use of this system addresses some of the shortcomings of self-adhesive membranes, as the heating allows the membrane to ‘flow’ together, providing continuity and complete coverage of joints, penetrations, and other details. These systems, however, require application by skilled installers and can be quite dangerous to use.
Regardless of the type of sheet membrane, one challenge with their use is ensuring all penetrations, joints, and other details are covered, providing complete continuity of the membrane. In addition, protection of these membranes is required with the use of a protection or drainage board, with rigid insulation also serving this purpose before coverage of the membrane.
Various fluid-applied membranes are available, including hot-applied, cold-applied, water-based, and solvent-based materials. Each type comes with its own set of benefits and limitations. One common advantage they all share is they provide a monolithic waterproofing membrane, addressing the joint and detail issues encountered
with sheet membranes.
Hot-applied rubberized asphalt membranes demand specialized equipment and installers; like the thermofusible membranes, they can be dangerous to apply due to the high temperatures required for material application. Cold-applied systems appear to be gaining in popularity for a number of reasons; they are typically sprayable, providing significant reduction in the applied costs of the materials, and they provide the continuity mentioned previously.
Fluid-applied membranes are offered in one- and two-component formulations, and it is essential to ensure the correct material is selected for the job. Some of these can be applied to ‘green’ concrete, while others cannot. Again, these membranes also require the use of a protection layer before being covered.
Blindside waterproofing membranes
For waterproofing applications on sites where there are limits to excavation or where standard waterproofing techniques are not an option, blindside waterproofing may be the only way to go. Blindside membranes are particularly effective in zero-lot-line construction as they allow for the membrane to be applied to the positive side—the preferred placement for any waterproofing membrane. Blindside waterproofing is becoming more common as major centres become more congested.
These materials can be applied horizontally, or installed vertically on the soil-retention system, and the concrete is then poured against the membrane. Two main types of these systems are used: bentonite waterproofing and composite sheet membranes.
Materials containing sodium bentonite consist mainly of expansive clay that, in the presence of water, expands and provides waterproofing of the substrate. The material is available in sheets or panels, and installed dry. Once in contact with water, it forms a monolithic membrane controlling the movement of moisture.
It is important to prevent bentonite membranes from becoming damp or wet on the jobsite before the concrete pour. This can sometimes be difficult on construction sites, but premature exposure to moisture causes the clay to swell prior to the concrete pour, and the effectiveness of the in-place membrane may be compromised.
A number of blindside sheet membranes are mechanically fastened to the soil-retention system. Concrete is poured against the membrane, which then forms a continuous mechanical bond to the concrete.
All these systems have been proven over time, but due to the complexities of the various types of substrates to which these systems are being applied, the critical factor in the performance of these systems are the details. Many also offer a number of accessory products to address the details and to ensure continuity.
Two main types of cementitious systems are available: crystalline and cementitious coatings, which consist of non-flexible and flexible formulations (the former being more cost-effective and the latter seeing more extensive use and offering better performance characteristics). Both these systems are breathable and can be applied on the positive or negative side of the structure. They are very commonly used in water-containing structures.
Crystalline technology works by forming crystals in the presence of water, plugging the pores, capillaries, microcracks, and other voids in the concrete. The crystalline materials consist of portland cement, silica sand, and proprietary chemicals. When combined with water, a catalytic reaction occurs that forms non-soluble crystalline fibres in the pores and capillaries of the concrete.
Crystalline waterproofing becomes integral with the concrete and can be used via various methods; it can be surface-applied, come in dry-shake form, or be added directly to the concrete during mixing.
Although an integral crystalline waterproofing system offers certain strengths that would appear to make it a preferred approach, numerous additional steps are required to provide a complete system. Integral waterproofing does not address construction or expansion joints, larger dynamic cracks, failing waterstops, penetrations, or poorly consolidated concrete. Crystalline products may be best-suited as part of a complete, combined system that would also incorporate a proper membrane on the positive or ‘wet’ side of the wall.
Flexible cementitious coatings are polymer-modified materials applied as a surface coating and, when compared to crystalline waterproofing, possess a significant number of advantages. They can be:
Additionally, in poorly consolidated concrete, these coatings can still provide the waterproofing performance required, whereas a crystalline material would not provide the same performance.
For specific applications requiring certain levels of chemical resistance, some cementitious coatings possess comparable performance characteristics to conventional cementitious coatings while also providing resistance to chemical attack. It is important to check with the manufacturer on each specific application and provide all chemical information to ensure the material is suitable for the given chemical exposure.
As is evident, selection and installation of the correct waterproofing system is not a simple decision—there are many factors that need to be considered to ensure the system will not only perform in the short term, but also over the life of the structure. It is important to assess the conditions, select a system that will perform under them, and ensure the system can be installed to ensure continuity and long-term protection of the structure. Moisture infiltration into a structure is pivotal to mitigating the risk of any immediate or longer-range problems, and no one solution is right for every situation.
Russell Snow, CSP, CTR, BSSO, LEED AP, is currently the building envelope specialist for W.R. Meadows. His main responsibility is the development of specifications at the architectural/engineering level, along with providing technical support to all members of the sales team, continent-wide. Snow has been with W.R. Meadows for 14 years; his experience includes building envelope, concrete restoration, and products used in the treatment of concrete. He is currently involved with a number of associations including the Air Barrier Association of America (ABAA) Technical Committee, National Air Barrier Association (NABA) board of directors, and ASTM and American Concrete Institute (ACI) committees. Snow is a Certified Specification Practitioner (CSP) under CSC. He can be reached via e-mail at firstname.lastname@example.org.
Source URL: https://www.constructioncanada.net/understanding-waterproofing/
Copyright ©2020 Construction Canada unless otherwise noted.