Waterproofing technology has advanced over the past several decades with the introduction of new materials and the promulgation of new standards. These advancements reflect the study of past failures and an increased awareness of common design errors. While most of the moisture intrusion occurrences in waterproofing systems remain at penetrations and vertical transitions, there have also been documented concerns with horizontal applications. A specific design/construction defect that has been eliminated within the past several decades is how sandwich slabs are constructed.
The practice of applying waterproofing between the structural slab and a wearing slab is commonly referred to as a sandwich slab. In the past, the waterproofing membrane was applied in isolation between the structural slab and the wear slab. This application method propagated shrinkage cracks from the structural slab below the membrane or movement from the topping slab above the membrane. To counteract this problem, the most common waterproofing system prior to the advancement of new materials in the 1980s was multi-ply bituminous built-up membranes without cover boards or thermal insulation, which were susceptible to splitting. (Splits largely occurred because these types of membranes have strain of less than 2 percent when they are exposed to low temperatures.) The movement and/or cracks created openings in the membrane that allowed for moisture infiltration.