Term Description

An aggregate used in lightweight insulating concrete formed by heating and expanding a micaceous material.


The resistance of a material to flow under stress. For bitumen, viscosity measurements are reported in centipoise (cP or cPs) at a specific temperature; as viscosity increases, flow rate decreases.


Resistant to flow under stress. See "equiviscous temperature (EVT)."


An open space or break in consistency.


A relative term expressing the tendency to form vapor.

Waffle slab

Structurally reinforced concrete roof deck construction cast with wafflelike arrangements of perpendicular ribs on the ceiling side. Standard configurations include 6-inch-wide ribs on 36-inch centers cast using square 30-inch forms and 5-inch-wide ribs on 24-inch centers formed using square 19-inch forms.


(1) High traffic and high-service-frequency areas on a rooftop, particularly those leading and adjacent to vents, hatches and heavy duty air-conditioning units; (2) materials or accessories such as traffic mats or pavers installed on rooftop surfaces to provide wearing surfaces for traffic and/or protect a roof system from damage resulting from rooftop traffic.

Wash coat

A primer typically provided on the back side of painted metal products to help protect the underlying metal from wear and corrosion.

Water and ice-dam protection membrane

A continuous membrane installed under steep-slope roofing materials in areas subject to ice damming or wind-driven rain that prohibits water that gets through the roof covering from getting into the structure; ice- and water-protection membranes classified by ASTM D1970 must also seal around fasteners.

Water cutoff

See "cutoff."

Water table

The level within the ground below which the soil is saturated with water.

Water testing

A flood test (often minimum 24 hours) or flowing-water test to evaluate the watertight integrity of a waterproofing system (not a damp-proofing system) under hydrostatic (standing water) or nonhydrostatic (flowing water) conditions. See "flood test" and "flowing-water test."

Water vapor pressure

The pressure of water vapor at a given temperature; the component of atmospheric pressure contributed by the presence of water vapor. See "vapor pressure."

Water vapor retarder

See ‚"vapor retarder.‚"

Water vapor transmission

A measure of the rate of transmission of water vapor through a material under controlled laboratory conditions of temperature and humidity. Customary units are grains/h•ft2. See "vapor diffusion."


The ability of individual, overlapping components to resist the passage of water without hydrostatic pressure.

Water-shedding roof system

A roof system that depends on gravity for quick drainage via water-shedding to prevent water entry into or through the system.


The quality of a membrane, membrane material or other component to prevent water entry.


Treatment of a surface or structure to prevent the passage of water under hydrostatic pressure.

Waterproofing assembly

An assembly of interacting waterproofing components including the deck, membrane and protection/drainage/insulation course.

Waterproofing membrane

(1) The part of a waterproofing system that has the primary function of excluding water; it does not include accessories such as drainage materials or protection boards. See "membrane;" (2) a continuous layer used as a treatment of a surface or structure to prevent the passage of water under hydrostatic conditions.

Waterproofing system

A system of interacting waterproofing components consisting at a minimum of a membrane but may also include protection, drainage and insulation courses, as well as waterstops, expansion and control joints, various flashings and counterflashings, and overburden such as pavers, cast concrete and wire mesh or rebars. It does not include the substrate.


(1) A diaphragm used across a joint as a sealant, usually to prevent the passage of water; (2) devices installed at the intersection of cold joints in concrete walls and slabs, walls and footings, or at vertical joints in concrete work as a secondary means of protection against water infiltration.

Wear course

The top layer of surfacing that carries pedestrian or vehicular traffic. Sometimes referred to as wearing surface.

Wearing surface

See ‚"wear course.‚"