Let’s start by explaining what a waterproofing membrane is. It is a continuous layer of thin, water-tight material laid over a surface. This, for example, is commonly done on a flat balcony. It can be applied above the structural slab and then again below the finish tiles, providing excellent protection to the structural slab and the steel reinforcement within.
In the case of tiled areas, it must be remembered that the tiles and the membrane should be laid over a sloping level of the screed. This ensures that water flows away from the building into drainage areas. The preparation of this slope is critical, and it is best to test the slope before tiling. Spray the area liberally with water; if any water pools, there is an issue with the screed angles and levels. Pooled water will seep into a slab over time. This is because general waterproofing membranes work by repelling water as it moves over them—they are not all specialised swimming pool waterproofing membranes, which are an entirely different application.
The waterproofing membranes we are discussing are composed of thin layers of waterproof material, typically 2 to 4mm thick. These come as sheet membranes (supplied in a pre-made layer) or liquid applications, which cure into a solid layer after application.
The key characteristics to look for in a membrane are flexibility, strength (flexibility forms part of this measurement), tear-resistance, and elongation (to cover cracks and move with structural shifts). A critical specification for outdoor membranes in Australia is UV stability.
Sheet-Based Waterproofing Membranes
These are purchased in roll format, unfurled on-site, and laid onto the surface to be treated. A bituminous waterproofing membrane is highly favoured by contractors. Bitumen (sometimes called asphalt) is recognisable by its sticky, black, and highly viscous nature as a semi-solid form of petroleum.
The two main types are:
- Torch-applied bituminous membrane: This is applied using a blowtorch to slightly melt the bitumen, which is then pressed onto the surface, bonding securely as it cools. The edges of adjacent membranes are overlapped by about 100mm and sealed using the same hot adhesive method. Joint points in any waterproofing system represent a potential weakness and must be executed with extreme care.
- Self-adhesive bituminous membrane: These feature a release liner that is removed during application. No torching is required, making it safer and faster to install, achieving excellent adhesion even at low temperatures. Overlapping of edges is also required with this product.
There are also PVC waterproofing membranes and composite waterproofing membranes. Composite options feature a fabric base that provides high strength and tear resistance, treated with a chemical coating for water resistance. While factory-produced for consistent quality, they are generally less flexible than bituminous solutions.
Liquid-Applied Waterproofing Membranes
As the name implies, this solution arrives on-site in liquid form and is sprayed or roller/brush-applied onto the target area. The liquid cures upon air exposure to form a seamless, joint-free membrane. By adjusting the quantity of liquid applied per unit area, the thickness can be adapted to meet site specifications.
While quick to apply, servicing very large areas over successive days can result in “cold joints” where an application window ends. This is easily managed by overlapping the new liquid membrane over the cured layer, as the product bonds seamlessly to itself.
A liquid-applied waterproofing membrane is often considered superior to sheet-based alternatives primarily because it is completely joint-free. However, this depends heavily on application care; if applied too thinly, breakage and tearing can occur. The substrate must also be properly prepared to ensure maximum adhesion.
If a concrete screed is applied over the membrane, the membrane can be roughened while wet by “sowing” a thin layer of sand over it to improve mechanical mechanical bonding.
Contemporary liquid rubber options offer excellent performance advantages, including systems with UV-protective coatings that block UV degradation at the roof surface. This extends the service life of sound roofs while reducing maintenance. A cool roof coating can reduce roof surface temperatures by up to 10°C or more, lowering interior cooling demands and minimizing thermal stress damage. Roof repairs last longer when sealed with an elastomeric rubber roof coating.
How to Choose the Right Waterproofing Membrane
When selecting a waterproofing specification, evaluate the following criteria:
- UV Stability: Verify that the UV resistance ratings are high enough to withstand severe Australian climate conditions.
- Elongation: The measure of stretchability, expressed as a percentage. Look for a minimum of 150%, though 200% provides better long-term protection.
- Breathability: Excellent waterproofing can inadvertently trap moisture inside a structure if it enters through an isolated weak point. Breathable membranes help release trapped moisture as water vapour where appropriate for the specific application area.
- Tear Resistance: High elongation does not guarantee tear resistance. Always verify the physical tear strength specifications.
- Abrasion Resistance: The capacity to resist physical wear, especially from foot traffic or subsequent trade work during construction.
- Chemical Stability: Assess how the membrane interacts with its environment. External basement walls, for example, require resistance to soil chemicals and acidic groundwater.
- Food Safety: Waterproofing membranes used for concrete drinking water tanks must be certified food-safe.
- Geometry: For complex architectural shapes (such as column and beam junctions), a liquid waterproofing membrane is preferred over sheet membranes to avoid folds and air pockets.
- Case Studies: Request localized project case studies where the membrane has performed successfully for a minimum of 8 to 10 years.
If you need specialized technical guidance for your project, please contact us today through our contact page. Our team is here to help you select the ideal compliant solution for your property.
For official guidance on external waterproofing compliance and standards within New South Wales, refer to the National Construction Code (NCC) and Australian Standards AS 4654.2. Australian Building Codes Board
