Selecting a Waterproofing System: Many Options, Which is Right for You?
- John D'Annunzio
- May 4, 2018
- 7 min read
When selecting a waterproofing system, conservatism is the word of the day. Remember, you only have ONE opportunity to do right, and failure of this system affects the entire building, it's occupants, and perhaps your businesses future. This is no joke. Structural decay, microbial growth leading to mold and "sick building syndrome," slip-and-fall liability and more all are directly and primarily linked to waterproofing issues. Nearly 70% of construction litigation involves waterproofing as the culprit. Studies have shown that water is the "main cause of microbial growth" in fully 65% of buildings. Now consider that 99% successful waterproofing is a failure. Consider that once water is in the building, it can and will migrate within the building, making the seemingly simple task of finding a link incredibly difficult. Make no mistake, to be considered a success, waterproofing must be 100% successful, especially below grade. Wow, you might be thinking. Stressful, and costly, right?
We're happy to tell you: wrong. Waterproofing is a small percentage of total construction costs but it is sneakily complex. Thus it pays to perform excellent research, due diligence, and quality control to ensure that all waterproofing issues are properly addressed. Site-specific issues and building requirements must play a central role, along with a few other key considerations:
Some major considerations are:
Occupancy and Purpose
Water Table
Soil Characteristics
Substrate Stability
Construction Sequence
Track record
Risk v. Cost
Ease of Application
Occupancy and Purpose
Important design factors to consider are leak risk tolerance and sensitivity to humidity of an occupied space. There are certain occupied spaces where leaks are more detrimental than others. For instance, leaks are intolerable in book storage, data centers, art storage, electrical switchgear, and medical facilities. These types of facilities also require tight humidity control, and balancing the humidity in a leaking building is extremely difficult. Intrusion of air can be as detrimental as water in sensitive facilities. Medical facilities, research and testing laboratories fit within these classifications. However, just because a building does not contain sensitive occupants or systems does not mean that waterproofing can be ignored. Leaks can create a crack cycle that can take down a parking garage or building. This is especially true in Northern climates, as in the Argo Lake Elliot Mall collapse.
Water Table Level
The water table level is an important consideration that not only determines the type of waterproofing required, by code it determines if waterproofing is required. The International Building Code requires that waterproofing or dampproofing is applied on all below-grade structures where the ground water table is maintained a minimum of 6 inches below the ground slab.
Accurate soil bearings – completed by a competent civil engineer – are required prior to waterproofing design. In the Northern Hemisphere the water table is usually highest after the spring thaws have saturated the ground and lowest following the summer evaporation of the surface moisture.
Soil Characteristics
Waterproofing materials are unique because they are exposed to much harsher conditions than any of the other building exterior components. Most of the exposure elements are continuously present at the waterproofing surface and do not dissipate as they do at the other exterior components. For example, water can be present in below-grade surfaces for weeks, whereas water on roof systems is to be removed within 48 hours.
Soil characteristics are a major determinant in both drainage but also material deterioration. Chemicals in the soil can have an adverse effect on some materials. Thus, knowledge of potential chemicals present is required for design. Chemical properties in soils can adversely affect waterproofing in various ways. Acids and alkaline in ground water can accelerate the deterioration of concrete and steel reinforcing bars. Salt in water corrodes reinforcing bars in concrete. Sulfates can have a negative reaction with Portland cement resulting in internal shearing stress that causes spalling. Other chemicals that affect waterproofing are calcium hydroxides, oils and chemicals from fertilizer.
The physical properties of the soil can also affect waterproofing. Clay soils of low permeability limit underground hydrostatic pressure. The intensity and nature of hydrostatic pressure can force water into tie-rod holes, cold joints and rock pockets. Hydrostatic pressure can also turn minor imperfections into probable sources of leaks.
Substrate Stability
Waterproofing is applied on substrate surfaces to protect the substrate from structural deterioration caused by water, chemicals and soil. The applied waterproofing material must also be capable of performance if the substrate becomes unstable or minor imperfections occur. Some substrates are inherently prone to imperfection and this should be considered prior to waterproofing design.
Waterproofing membrane applied over substrates that are vulnerable to cracking from any source must be elastic and capable of resealing. Cracks can occur in masonry or other waterproofed components that have multiple construction joints. Dampproofing should not be considered in these conditions.
The types of soils at the site can also have an impact on substrate stability. Expansive soils and peaty soils can produce rising and settling footings that cause cracks in footings and foundation walls. All substrate openings can become potential points of moisture infiltration.
Construction Sequence
Waterproofing is applied in phases as construction of walls and plaza decks are installed. There may be extended periods of time between certain waterproofing applications and final completion. For instance, waterproofing of below-grade walls is typically done in 6- to 8-foot increments from the bottom to the top. The initial section is finished, the site is backfilled and the waterproofing applicator uses the backfill as a scaffolding to complete the next increment. This process is continued until the full wall is waterproofed. This process could continue over an extended time period because the waterproofing applicator relies on the pour schedule and backfilling operations.
Installed waterproofing materials are rarely exposed to exterior elements after final application procedures are completed. The membranes are covered by soil, concrete or another type of top surfacing. However, because of the initial construction sequence, these materials may be exposed for an extended period of time. This fact must be considered in the material selection process.
It is important to prevent the exposure of vulnerable materials to the elements when long delays in the schedule occur. Waterproofing materials must be capable of withstanding freezing temperatures if they are to be exposed to these conditions for more than one week. Exposure to rain and water can also be a concern. If bentonite clay is used it must be adequately covered.
Membranes with a low resistance to ultraviolet radiation can deteriorate if the materials are exposed to sunlight for intervals as short as one month. If the waterproofing is applied prior to the completion of the structural elements it may prompt negative effects on the waterproofing such as deflections or other imperfections.
Track Record
In the last decade the waterproofing market has become very competitive and manufacturers that provide other exterior building component materials – primarily roofing – have entered the market. Some of these products are well suited for these types of applications; some are not! Remember that as a designer, you get only one chance to do this right. One simple way to evaluate a product is to check its track record in similar waterproofing applications. Sources of information could include other designers, building owners, contractors or specialty consultants.
It could also be beneficial to ask specific questions of the manufacturers. The first question should be: Is the product manufactured by the seller or is the seller merely a distributor (private label agreement). This is very common in the construction materials industry. Manufacturers typically private label some – or all – of the system components. This type of information is available through Dun & Bradstreet.
What is the manufacturer’s track record? Contact other designers or waterproofing contractors in your area or throughout the country to find out their history with these materials. This is a small industry and material performance – good or bad – is usually a topic of conversation. If you talk to other industry professionals or manufacturers it would also be important to find out if the product has a history of successful performance under comparable conditions for at least 15 to 20 years. Obviously, if the product has not performed in the past it is safe to assume it will have the same difficulties on your project. Designers should also be skeptical of other building component materials being marketed for waterproofing applications without a track record in similar conditions. No other building component is exposed to the conditions of waterproofing materials.
Another important consideration is whether the material has maintained a consistent formulation for the past 10 years. This is a significant concern at this time. Environmental regulations and depletion of natural resources have had a large impact on current material formulations. Products that we have relied on for hundreds of years are not as readily available. This has left the industry with unstable materials and formulations with no verifiable track record.
Risk vs. Cost
The designer should always minimize risk despite any reasonable – or unreasonable – costs. If a building owner or general contractor wants to cut costs, the waterproofing system is not the place to do so. The cost of excavation for repairs – even minor repairs – far exceeds the initial cost of the waterproofing. That said, there are ways to minimze risk, or maintain the same risk profile, while saving costs. When considering costs it is CRITICAL to consider lifetime costs for the building. Maintenance of waterproofing systems is very expensive relative to many other building systems, and failure of a waterproofing system can be financially catastrophic. Remember, as a designer you only have one chance to do it right!
Ease of Application
Ease of application is a minor factor, however, it may result in better workmanship, so it should be considered. There will also be projects where access or space constraints are an issue. Application methods, particularly material adhesion methods, may be determined by the site constraints. On projects where other factors are in balance, ease of application of a material or a system can be a determining factor in material selection.
To summarize, there are many considerations when selecting a waterproofing system and design. These designs should not be "out of the box." Instead, they should be proven, examined, and due diligence should be done to ensure that the system has a proven track record in the same environment that it is proposed for. If it does not, chemical resistance, site testing, and design by a waterproofing expert can save the owner huge amounts of money and risk in the long term.
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