Dampproofing is the treatment of a surface or structure to resist the passage of water in the absence of hydrostatic pressure. Dampproofing methods will not work when hydrostatic pressures are present, and are generally employed above grade, or below grade in the absence of ground water. For this reason, many of the factors that are critical to the performance of a waterproofing system are not as important.
Dampproofing is the treatment of a surface or structure to resist the passage of water in the absence of hydrostatic pressure. Dampproofing materials need only resist the capillary action of moisture as it attempts to pass into or through the structure. Dampproofing methods are generally employed above grade, or below grade in the absence of ground water; to reduce dampness within the structure.
Dampproofing methods should not be used for horizontal slabs-on-grade or foundation walls when these structures will be subject to hydrostatic pressure. Dampproofing methods also should not be used on structural decks over habitable space or on planters, pools, or other water containment structures. Instead, waterproofing materials should be used in these locations.
Vapour retarder materials are often used for dampproofing floor slabs-on-grade that are not subject to hydrostatic pressure. In this type of application, aggregate fill is first placed on the earth. Polyethylene or premolded membrane sheets are laid over the aggregate fill, and the concrete slab is poured over the vapour retarder sheets. The vapour retarder restricts moisture from the ground from penetrating into the floor slab, and it prevents the concrete from contaminating the aggregate fill during placement.
Solvent-based bituminous mastic and bituminous emulsion are often used on concrete foundation walls along with geocomposite and foundation hydrostatic pressure relief systems. The dampproofing material is generally sprayed, brushed, or applied by trowel directly to the concrete wall surfaces. Masonry walls are prepared with a minimum 12.7 mm (1/2 in) thick parging.
Masonry load-bearing and curtain walls above grade are common locations where dampproofing materials are used. Above-grade masonry construction of this type may need to be protected from rain and prolonged water exposure. Such moisture penetration can threaten interior finishes. Bituminous dampproofing materials can be applied to the interior side of walls above grade, but usually require that they be covered with furring and drywall or other finish.
For aesthetic reasons, dampproofing applied to the exterior of walls above grade is usually transparent or is a material that can provide an attractive finish. Transparent dampproofing materials usually consist of silicones, acrylics, or polymeric resins that penetrate the surface of the masonry and seal its pores.