ABSTRACT This presentation will educate the audience about the fundamentals of below-grade waterproofing. With high costs, many functions are being placed in below-grade loca¬ tions. Classrooms, laboratories, auditoriums, and other critical occupancies require a completely watertight environment. This presentation will discuss the various below-grade waterproofing options available, along with recommended materials and installation methods. Below is an outline of the presentation: SPEAKER Edward Stewart is a Registered Roof Consultant and certified construction supervi¬ sor. He has specialized in building renovation projects for 25 years and has extensive experience in evaluating and designing roofs, walls, windows, plaza decks, green roof¬ ing, and weatherproofing systems. Mr. Stewart has given numerous educational pre¬ sentations at client and peer associations throughout the U.S. He is a member of the National Roofing Contractors Association, the U.S. Green Building Council, and RCI. CONTACT INFO: ejs@gainc.com or 800-659-4753 COAUTHOR Catherine A. DuPont is a structural field engineer for Gale Associate’s building enve¬ lope technology group. She is responsible for structural engineering and building envelope evaluations and fieldwork for building projects, including investigations, analysis, design, coordination, specifications, and construction administration. Ms. DuPont holds a BS degree in civil engineering from Tufts University. Stewart and DuPont – 1 82 Proceedings of the RCI 24th International Convention
The goal of a properly de¬ signed and executed below-grade waterproofing system is to prevent passage of water into occupied space or structural building com¬ ponents. When designing a water¬ proofing system, specific guide¬ lines should be followed to ensure long-term performance. Product selection will often depend on a number of environmental factors, including water sources and the presence of soil contaminants. A waterproofing design professional should be included on the build¬ ing envelope and structural design team so as to develop an interconnected waterproofing sys¬ tem. Successfully designed and installed waterproofing will pro¬ tect interior finishes and equip¬ ment, reduce the weatherization of structural concrete and masonly, and provide a comfortable indoor air quality environment for building occupants. While each project varies in site conditions and building configuration, the following basic concepts should be considered during the selection and design of a waterproofing sys¬ tem. REVIEW OF AVAILABLE INFORMATION The first step in designing an effective waterproofing system is to review various sources of infor¬ mation that can typically be pro¬ vided by the architect, geotechni¬ cal engineer, and structural engi¬ neer. Each of the following will ultimately influence the designer’s waterproofing system selection: Water Sources Water sources, including cap¬ illary action, hydrostatic pres¬ sure, and gravitational water, are Photo 1 – View of compacted, engineered backfill material prior to application of waterproofing and pouring of the concrete foundation slab in a blindside application. typically encountered in belowgrade applications. Capillary action can be defined as the act of water wicking through or into a porous substrate via tiny voids in the material. Hydrostatic pres¬ sure on a vertical surface occurs due to the weight of the water in the soil above a point. Water pas¬ sage under hydrostatic pressure is of special concern, as it travels through the path of least resis¬ tance, and therefore, any defects or areas of weak termination may be a path for travel. Gravitational water is allowed passage through soil by means of gravity (e.g., rain¬ water that collects on the ground’s surface and percolates down through the soil due to gravity). A geotech report is a pri¬ ority so as to determine the height of water tables, presence of sub¬ grade systems, or even the effect of tides on a water table. Environmental Conditions Environmental conditions to be considered generally include the presence of soil contaminants, high acidic content in soil, and chemical contaminants. Material selection is critical, since particu¬ lar salts, acids, or alkalis present in soils can inhibit bentonite clay’s ability to swell. In some cases, the soil itself (such as marine clays) can shrink and swell and could influence perfor¬ mance. Over recent years, water¬ proofing materials such as PVCs have been developed to be more resistant to common soil contam¬ inants, including salts, alkali, petroleum, and sulphates. Proceedings of the RCI 24th International Convention Stewart and DuPont – 1 83 Photo 2 – Installation of a positive-side waterproofing system. Structural Drawings Structural drawings should be obtained from the architect and/or structural engineer prior to considering a waterproofing system. Structural drawings will indicate if both horizontal and vertical surfaces are to be waterproofed or if blindside waterproofing is re¬ quired. Often, accessibility will limit the type of prod¬ ucts that are suitable for use. A combination of vari¬ ous waterproofing materials may be required to address varying conditions on the same site. The number of penetrations and complexity of building transition details can also be determined during the structural drawing review. A large number of penetrations and over¬ ly complicated detail transitions may affect the designer’s decision to use a liquid, or spray-applied waterproofing versus a sheet membrane. Soil and Geotechnical Reports Soil and geotechnical reports, in conjunction with a structural analysis, will indicate any antici¬ pated settlement of the structure. Where soft soils are present and slab settlement is anticipated, the waterproofing material should have the ability to accommodate limited amounts of differential movement and bridge any crack¬ ing and expansion joints. The type of soil to be used for backfill, whether it be the existing soil on site or a well-graded backfill material, should be reviewed by the design professional. Typically, aggregate should not be less than % inch to provide a well-drained soil environment surrounding the waterproofing. Additionally, soil with large or sharp rocks should not be used for backfilling appli¬ cations, as damage to the water¬ proofing material may occur. Post¬ consolidation of backfill can be a major problem, so attention dur¬ ing backfill operations is extreme¬ ly important. Backfill should be specified to be compacted to the manufacturer’s requirements and in accordance with ASTM D 1557, “Test Method for Laboratory Com¬ paction Characteristics of Soil Using Modified Effort.” When selecting the water¬ proofing location, two applica¬ tions are considered: • Negative side applies to the face of the structure which is not directly exposed to water or hydrostatic pressure. Neg¬ ative-side water¬ proofing is typi¬ cally used for property-line con¬ struction, where excavation of the site is not feasi¬ ble. Negative-side waterproofing that is accessible from the interior of the building can be beneficial, since it allows for repair access. However, under hydrostatic con¬ ditions, the wa¬ terproofing sys¬ tem is susceptible to failure, as it is not confined by a structure or backfilled soils. • Positive (blind) side is the face of the structure exposed to water or hydrostatic pres¬ sure. Positive-side water¬ proofing applications are widely accepted by industry professionals as a more effec¬ tive system, as they act as barrier systems preventing water from entering the structural components and thus reducing the potential for corrosion of embedded steel in concrete. Addi¬ tionally, in a positive-side application, the waterproof¬ ing system is sandwiched between the backfill soil or mud slab and the structure and can be partially or fully adhered or loosely fastened. DESIGN SELECTION CRITERIA The process of selecting an effective and feasible waterproof¬ ing system will also depend on a number of other factors. The design professional should con¬ sider the following: Photo 3 – View of unconfined and prema¬ turely hydrated bentonite waterproofing. Bentonite waterproofing can swell up to 15 times its dry volume. Stewart and DuPont – 1 84 Proceedings of the RCI 24th International Convention Construction Sequencing • How long will concrete have to cure prior to waterproofing installa¬ tion? • Will backfilling occur im¬ mediately after water¬ proofing installation? • Who will be responsible for substrate preparation? • What is the acceptable ap¬ plication temperature? Installation • Is the local workforce ex¬ perienced with applying specified materials? • How will difficult building transition details or flash- Figure 1 – Typical cross section of positive-side waterproofing system components. ing configurations be ad¬ dressed? Will the waterproofing be ap¬ plied to cast-in-place con¬ crete, precast concrete, or lagging? WATERPROOFING SYSTEM COMPONENTS Although not all components referenced in Figure 1 are re¬ quired for a complete waterproof¬ ing system, all are commonly uti- Nontechnical Provisions lized within the industry. Depend¬ ing on on-site characteristics, in¬ cluding the height of the water table, code requirements, and the use of subgrade drainage sys¬ tems, the designer may consider a combination of the following com¬ ponents to be included in his or her waterproofing design: • Surface primer • Waterproofing membrane • Protection layer • Drainage composite • Insulation • Site slope and subgrade drainage options • Filter fabrics (as required for subgrade drainage systems) DETAILING AND INSTALLATION The majority of waterproofing failures occur not through mater¬ ial deficiency or failure, but from poor workmanship or inappropri- What is the cost? ■ II • What type of manufac¬ turer warranty is available to the owner? Unfortunately, poor construction sequencing can result in damaged waterproofing that may ultimately require costly re¬ moval and replacement. For example, a one-week delay in backfilling over a bentonite-based water¬ proofing system applied to a horizontal surface ex¬ posed to rain may result in prematurely hydrated clay. Hydrated bentonite, when not under confinement pressure provided by a compacted backfill, is beyond repair and requires removal and replacement. Photo 4 – Ribbed polyvinyl chloride (PVC) waterstop embedded in con¬ crete. Proceedings of the RCl 24th International Convention Stewart and DuPont – 185 Photo 5 – Preparation of substrate by blow¬ ing debris from concrete footing. ate detailing by the design profes¬ sional. The waterproofing and building envelope components need to act as one system, with each component affecting the overall performance. Detailing and building transitions require close attention from design pro¬ fessionals. Construction joints, expansion joints, penetrations, and terminations are all weak points where the likelihood of leakage is the greatest on a belowgrade waterproofing system. Construction Joints Where penetrations and con¬ struction joints or “cold joints” exist in a below-grade structure, waterstops should be installed as a means of preventing the trans¬ mission of water through that location. Even with the installa¬ tion of full positive-side water¬ proofing, waterstops must be included as redundancy to the primary waterproofing system. Waterstops come in a variety of shapes and materials, including polyvinyl chloride (PVC), neo¬ prene, thermoplastic rubber, ben¬ tonite clay, asphalt, plastic, and hydrophilic materials. Waterstops should be installed on the wet side of the reinforcing steel to act as a barrier against corrosion. Care should be taken by the design¬ er to ensure that waterstops are spec¬ ified and installed at all cold joint and penetration loca¬ tions. A combination of an embedded PVC and swellable ben¬ tonite or hydrophilic waterstops is recom¬ mended. The redun¬ dancy of a water¬ proofing membrane and waterstop to prevent transmis¬ sion of water is criti¬ cal to a successful waterproofing sys¬ tem. Surface Preparation Most waterproofing mem¬ branes are applied to concrete or wood surfaces. With the majority of waterproofing being applied to concrete surfaces, surface prepa¬ ration is critical to obtain a welladhered, nonpuncture-susceptible waterproofing membrane. Design documents should include manufacturers’ expectations of what is acceptable with regards to substrate preparation. Although various manufacturers’ opinions may differ, concrete should typi¬ cally be smooth and clean from loose debris. Bugholes, honey¬ combs, and voids in the concrete should be patched with a non¬ shrink grout or an acceptable patching cement. Poorly compact¬ ed concrete, typically found at the base of the wall, should also be filled. Small cracks in a concrete wall may require grinding and patching or a reinforcement appli¬ cation of the waterproofing sheet membrane. Note that specific substrate preparation methods and details are product- and manufacturer -dependent. The de¬ sign professional should consult with the manufacturer’s represen¬ tative for typical substrate prepa¬ ration requirements. Waterproofing Material Selection Based on the site conditions, owner expectations, and costs associated with installation, the selection of the waterproofing material and composition may vary. Typical waterproofing sys¬ tems include but are not limited to the following: • Fluid-applied systems, which are typically water- or sol¬ vent-based, and cure to a monolithic, rubberized solid. Fluid-applied systems are typically installed cold; how¬ ever, hot-applied, asphalt¬ based products are available. These systems have a num¬ ber of derivatives including urethane, rubber, asphalt, and coal tar. Many applica¬ tors and designers prefer a fluid-applied system for a structure with overly compli¬ cated penetrations and detail transitions, as these products are typically “self-flashing.” They also tend to accommo¬ date structural movement, as they are considered to be highly resilient. However, obtaining an acceptable dry¬ film thickness of the finished product is imperative for product performance and may be workmanship-depen¬ dent. Additionally, the cured, fluid-applied system can be susceptible to punctures on the job site and requires a protection board to be installed once curing is com¬ plete. Some fluid-applied sys¬ tems are not considered suit¬ able for high hydrostatic head conditions on negative-side applications. It is recom¬ mended that concrete be allowed to cure for a mini¬ mum of seven days, prefer¬ ably 28 days. Blistering may occur if water is trapped beneath the membrane. Stewart and DuPont – 1 86 Proceedings of the RCI 24th International Convention • Sheet membrane systems, including but not limited to thermoplastic, elastomeric, and rubberized asphalts, are typically installed in a single¬ ply membrane application. While sheet membrane sys¬ tems are manufactured to a uniform thickness, high qual¬ ity workmanship is required when detailing penetrations, joints, and seams. Unlike fluid-applied systems, sheet membranes should be shin¬ gled when installed to allow for the shedding of water. While sheet seam preparation and detailing differs, based on the manufacturer, a suffi¬ cient material lap and/or reinforcement sheet is typi¬ cally required. Sheet-applied systems are also susceptible to fishmouths and blisters during the installation and alignment of the sheets. Sheet membrane systems can be loose-laid or fully adhered. Photo 6 – Blister in a fluidapplied waterproofing applica¬ tion. • Bentonite or natural clay sys¬ tems have the ability to swell when exposed to water. Under proper confinement and when applied to properly prepared concrete, bentonite can be self-sealing and act as an excellent barrier to water. Exposure to water activates the clay. Phased construc¬ tion, where the clay may be exposed to weather for long periods, is not recommended, and backfilling immediately after installation is preferred. However, bentonite sheet waterproofing is favorably utilized in blind-side applica¬ tions for foundation slabs where the concrete is poured directly onto the laid water¬ proofing sheets. The curing of the concrete in conjunction with the bentonite clays cre¬ ates a strong bond. It should be noted that a geotech report is critical in determining the presence and locations where subgrade streams and tidal water tables exist, since such conditions can wash out or cause wet-dry cycle failures of bentonite. CONCLUSION For a below-grade waterproof¬ ing system to be successfully exe¬ cuted, the design professional should review all available materi¬ als related to site conditions, structural detailing, and interior usage. Proceedings of the RCI 24th International Convention Stewart and DuPont – 1 87
