Hurry-up and wait used to be standard practice when it came installing effective below-grade waterproofing on large projects such as parking garages. Architects wanted to select the correct components to provide long-term protection and durability on a project for their clients. They weren't as concerned about any delay this desire may have caused to the contractor doing the work.
Fortunately for foundation contractors, waterproofing materials have evolved into products that not only protect structures well, but their application can be streamlined into every project's critical path task schedule.
Cary Robertson, product manager for Henry Co., a Los Angeles-based manufacturer of waterproofing materials has witnessed the change. “Thirty years ago contractors followed a labor-intensive procedure,” said Robertson. They first brushed on a below-grade waterproofing product consisting of an asphaltic coating. Then they embedded a layer of fiberglass reinforcing mesh into the wet coating and allowed it to dry before applying additional coats of asphalt and reinforcing. “The deeper the structure was below grade, the more layers they had to apply,” said Robertson.
To avoid this tedious work, manufacturers developed what became the mainstay of the vertical waterproofing industry. Designers and contractors alike opted for the self-adhered membrane—also known as the ‘peel-and-stick' membrane. The product is made up of a self-adhering rubberized asphalt compound, factory-applied to a strong high-density polyethylene carrier film. Installation of the peel-and-stick membrane typically requires 7 to 14 days of cure time after the forms are removed, and the concrete should be dry prior to application. A solvent- or water-based primer is applied to the concrete surface and the self-adhered waterproofing membrane should be applied that same day. Primed surfaces not covered by membrane during the same working day must be re-primed. “The big advantages of peel-and-stick membranes are the factory controlled thickness and the ease of installation,” notes Robertson.
But self-adhered membranes require numerous 2- to 3-inch overlapping seams on adjacent rolls to form a continuous waterproof membrane. These seams, if not properly aligned, can form gaps or fish-mouths between sheets, providing an opening for water penetration. “How good it works is dependent on how well it is applied,” says Robertson. And the self-adhered membrane must be applied to concrete that is dry and sufficiently cured. But despite those limitations, the self-adhered membrane is a good waterproofing material that is still used today.
But Robertson says now, the industry can't always wait for the concrete to cure 7 to 14 days; contractors want the job to move along faster. So, a number of water-based, spray-applied membrane systems are becoming popular for waterproofing below-grade. The coverage you can get with a spray-applied system is far superior, but according to Cary Roberson, “the performance is as good as the contractor doing the work—he must control the thickness properly”
An effective waterproofing coating must maintain a thickness of around 60 mils. Consistent application is essential. This technology also can be applied to damp or green concrete. Robertson explains, “Contractors like this method because they can spray large areas of wall quickly, on partially green concrete, and they don't have to worry about seams.” Modern spray-applied membranes allow for fully adhered seamless protection in one efficient pass. This method is impacting contractor productivity and construction schedules, allowing work to be streamlined and eliminating waiting periods.
Robertson and other industry experts warn contractors considering entering into the below-grade waterproofing business that it shouldn't be attempted without training and appropriate equipment. “One good source of information is the Sealant, Waterproofing, and Restoration Institute,” said Robertson.
Cary Robertson is product manager, building envelope systems, Henry Co.
For more information, contact him at email@example.com.