Waterproofing is the treatment of a surface or a structure to prevent the passage of liquid water under hydrostatic pressure. The positive prevention of movement of water under pressure is what distinguishes waterproofing from dampproofing. There are various forces that can act alone or together to force water through concrete. They are hydrostatic pressure, capillary action, wind driving of rain, a difference in vapor pressure between the two sides of the concrete, or some combination of these. Water finds its way most readily through porous concrete, cracks, structural defects, or through joints that have not been properly designed, built or sealed. This article discusses the installation of barrier systems on concrete surfaces as well as waterproofing materials available.
Following are some of the considerations to keep in mind when choosing a waterproofing system: longevity, a particularly important consideration if the barrier system will be covered with earth or will otherwise be inaccessible for repair; wear resistance, a factor on roofs, parking decks, bridge decks and other areas subject to traffic; ability of the liquid to form a continuous film under the conditions expected on the job; ability to flow, stretch or reform sufficiently to span any crack that forms in the concrete after the barrier has been applied; bondability to the concrete; and compatibility with any other materials with which it may come in contact, such as flashings, joint sealants or other adjacent membranes.