Developments in Below-Grade Waterproofing

Costly failures in below-grade waterproofing systems in recent years have driven owners and designers to seek high-performance and reliable solutions to prevent moisture infiltration. Careful consideration of site conditions and construction methodologies can lead to successful selection and installation of below-grade waterproofing assemblies so that future remedial work is limited. There are two types of installation methods for below-grade waterproofing, typically referred to as positive-side or blind-side. Negative-side remedial repairs refer to waterproofing installed after completion of construction. Membrane selection depends on construction method, the potential for hydrostatic pressure, the ground water elevation and owner tolerance for risk of water intrusion. The construction industry has utilized modern waterproofing membranes for several decades with success, but recent failures have led to the development of membranes that introduce measures of redundancy by combination of materials and techniques to create hybrid products. Various manufacturers have marketed hybrid systems with added warranty incentives to motivate the construction industry to adopt higher standards of practice. Conversely, waterproofing admixtures, when introduced into concrete mixes, offer some integral waterproofing capabilities with the option to omit a membrane. Hydrophobic and hydrophilic admixtures work in conjunction with a particular mix design to prevent transmission of moisture by preventing water transfer through small cracks. Admixtures can also be crack reducers but have not shown they prevent all cracks in concrete. The increased use of shotcrete as a wall casting method on projects has presented challenges for waterproofing below-grade spaces, and industry professionals are continuing to seek solutions to accommodate projects with shotcrete construction. Specifically, designers and manufacturers seek to marry material types and installation procedures that will remain watertight for the lifespan of the building. To avoid failures, new developments in waterproofing membranes, such as pre-installed injection ports or dual membrane hybrid systems offer the designer the ability to compensate for potential weakness in the waterproofing scheme. Below-grade spaces offer few choices for repair due to inaccessibility, and the development of new redundant waterproofing methods with more comprehensive warranties is a welcome addition to industry practice.