Waterproofing Glossary

A reference guide to the terms you’ll come across when researching waterproofing, from the different membrane types to the technical language contractors use during inspection and quoting. Each term links to a fuller guide where one exists.

Waterproofing Membrane

A waterproofing membrane is a continuous, water-resistant layer applied over a surface, such as a roof, slab, or wall, to prevent water penetration. Membranes can be liquid-applied (curing on-site into a seamless layer) or sheet-based (pre-manufactured rolls joined at the seams). The membrane’s job is to create an unbroken barrier between the structure and the weather; how well it does that depends on the material, the application method, and how many joints or seams the system has, since every joint is a potential failure point. Membrane choice depends heavily on the surface, its exposure, and how much thermal movement it undergoes.

Liquid Rubber

Liquid rubber is a cold-applied waterproofing system sprayed, rolled, or brushed directly onto a surface, where it cures into a single, fully bonded, seamless membrane. Because no flame, solvents, or primers are required for most applications, it can be installed over a wide range of substrates, including concrete, metal, asbestos, and tile. Its defining property is elasticity: a good liquid rubber system can stretch up to 800% without cracking, allowing it to move with a structure through thermal expansion instead of fighting against it. See our full comparison guide for how it stacks up against other systems.

Bituminous Waterproofing

Bituminous waterproofing uses bitumen-based materials, including torch-on felt, pour-and-roll bitumen, and modified bitumen sheets, to form a waterproof layer, typically on flat concrete roofs. It has been used for decades and remains a relatively cost-effective option per square metre. Installation involves either heat (torch-applied) or solvents, and the sheets are joined with overlapping seams that must be sealed correctly. Every seam represents a potential entry point for water, which makes bituminous systems less forgiving on roofs with complex geometry, multiple penetrations, or frequent changes in level.

Cementitious Waterproofing

Cementitious waterproofing is a cement-based slurry, brushed or sprayed onto masonry or concrete, that bonds chemically with the substrate to form a rigid, waterproof layer. Unlike liquid rubber, it does not flex significantly, which makes it well suited to below-ground applications like basements, retaining walls, and water tanks, where thermal movement is minimal. On an exposed roof subject to daily heating and cooling, that same rigidity becomes a liability, since cementitious coatings are prone to hairline cracking as the structure beneath them expands and contracts.

Sheet Membrane

A sheet membrane is a pre-manufactured waterproofing material, either self-adhesive or mechanically fixed, that’s rolled out across a surface and joined at the seams. Because quality control happens at the factory, sheet membranes offer more consistent thickness than some liquid-applied systems. The tradeoff is the same one bituminous systems face: every seam and overlap is a potential entry point, and sheet membranes handle irregular shapes, corners, and multiple penetrations less cleanly than a system that cures into one continuous surface.

Box Gutter

A box gutter is a built-in, rectangular guttering system typically formed into a roof’s structure rather than hung externally, often found where two roof sections meet or run parallel. Box gutters are a common failure point because they hold standing water, involve multiple joints and corners, and are harder to inspect than an open gutter. A seamless, fully bonded membrane such as liquid rubber is generally the preferred waterproofing solution here, since it can follow tight corners and penetrations without relying on sealed joints.

IBR Roofing

IBR (Inverted Box Rib) is a type of corrugated metal roof sheeting widely used in South Africa for both industrial and residential roofing. Its profile includes alternating trapezoidal ribs that give it structural strength. Over time, IBR roofs develop rust at screw penetrations, lap joints, and cut edges, which is where water ingress typically begins. Liquid rubber waterproofing can be applied directly over existing IBR sheeting to seal these vulnerable points without needing to strip and replace the roof.

Damp-Proofing

Damp-proofing is a treatment that resists the passage of moisture vapour through a wall or floor, typically used below ground level or in areas not directly exposed to rain. It is a different function from waterproofing, which stops liquid water under direct exposure and, often, under hydrostatic pressure. Confusing the two is a common and costly mistake: a roof or exposed wall needs waterproofing, not damp-proofing, because damp-proofing is not designed to withstand direct rainfall or standing water.

Encapsulation

In waterproofing, encapsulation refers to sealing a surface, most often an asbestos roof, under a continuous membrane rather than removing the original material. A liquid rubber encapsulation system bonds directly over sound, non-friable asbestos sheeting, locking the fibres in place while also waterproofing the surface. This is significantly less expensive and disruptive than full asbestos removal, and is a common, code-compliant approach for older industrial and residential roofs.

Thermal Movement

Thermal movement is the expansion and contraction a building material undergoes as its temperature changes throughout the day and across seasons. Roofs are especially exposed to this, baking in direct sun and cooling rapidly at night, which places continuous stress on any waterproofing system applied to them. Materials with high elasticity, such as liquid rubber, are designed to move with this cycle without cracking, while rigid systems like cementitious coatings are more prone to fatigue cracking over time under the same stress.

Seamless Membrane

A seamless membrane is a waterproofing layer with no joints, seams, or overlaps, formed by curing a liquid-applied product directly on the surface rather than joining pre-made sheets. Because water reliably finds its way through joints before it finds its way through an intact membrane, a true seamless system removes the single most common failure point in waterproofing. Liquid rubber is the primary example of a seamless system used on complex roofs, gutters, and penetrations.

Cold-Applied System

A cold-applied waterproofing system is one installed without heat, open flame, or torching, typically by spraying, rolling, or brushing a liquid product directly onto the surface. Liquid rubber is the most common cold-applied system. The absence of flame makes cold-applied systems safer to install on occupied buildings and more forgiving around timber, insulation, and other flammable materials than torch-on bituminous alternatives.

Torch-On Application

Torch-on application is an installation method for modified bitumen membranes, where a propane torch is used to heat and melt the underside of the membrane, bonding it to the roof surface as it’s rolled out. It’s a well-established technique but requires trained operators and carries fire risk, particularly around timber roof structures, which is why cold-applied alternatives like liquid rubber are often preferred on occupied or sensitive buildings.

Primer

A primer is a preparatory coating applied to a surface before the main waterproofing membrane, improving adhesion between the substrate and the membrane above it. Not all systems require one: many modern liquid rubber products are formulated to bond directly to concrete, metal, or asbestos without a separate primer coat, which simplifies installation and reduces the number of steps that could be skipped or done incorrectly.

Substrate

The substrate is the underlying surface that a waterproofing membrane is applied to, such as concrete, metal sheeting, asbestos, or masonry. The substrate’s condition, whether it’s clean, dry, structurally sound, and free of loose material, directly determines how well a membrane bonds and performs. Skipping proper substrate preparation is one of the leading causes of early waterproofing failure, regardless of how good the membrane product itself is.

Hydrostatic Pressure

Hydrostatic pressure is the force exerted by standing or trapped water against a surface, such as a basement wall holding back groundwater or a flat roof with pooling water. Waterproofing systems intended for surfaces under hydrostatic pressure need to resist water being actively pushed through, not just resist surface wetting, which is a higher performance standard than waterproofing a surface that simply sheds rainfall.

UV Degradation

UV degradation is the breakdown of a material’s chemical structure caused by prolonged exposure to ultraviolet radiation from sunlight, leading to brittleness, cracking, and reduced elasticity over time. Roof-facing waterproofing systems are under constant UV exposure, so product quality and UV-stable formulations matter significantly for how long a membrane will actually perform before it needs recoating or replacement.

Spalling

Spalling is the chipping, flaking, or breaking away of a concrete surface, usually caused by water penetrating the concrete and corroding the embedded steel reinforcement inside it. As the rusting steel expands, it exerts pressure from within, cracking and pushing off chunks of the surrounding concrete. Spalling is a structural warning sign, not a cosmetic one, and it’s exactly the kind of damage that waterproofing is meant to prevent by keeping water from reaching the reinforcement in the first place.

Flashing

Flashing is a thin material, typically metal, installed at roof joints, edges, and penetrations (such as where a chimney or pipe meets the roof) to direct water away from vulnerable junctions. Flashing works alongside the main waterproofing membrane rather than replacing it; poorly installed or corroded flashing is a common source of leaks even on an otherwise well-waterproofed roof, since it’s often the first point where a gap can open up.