Torch-On Waterproofing Membrane Guide for Sydney

Torch-on waterproofing membranes are a tried-and-tested solution that has been protecting Australian buildings for decades. Made from modified bitumen reinforced with polyester or fibreglass, these membranes are applied using a gas torch that melts the underside of the membrane, bonding it to the substrate as it is rolled out. Torch-on membranes are the industry standard for roofs, balconies, podium decks, and other external waterproofing applications across Sydney and NSW.

At Waterproofing Sydney, our licensed applicators have extensive experience installing torch-on membrane systems on projects ranging from small residential balconies in the Eastern Suburbs to large commercial roofs across Greater Sydney. This guide explains everything you need to know about torch-on waterproofing membranes, including how they work, where to use them, installation best practices, and how they compare to other membrane types.

What Is a Torch-On Membrane?

A torch-on waterproofing membrane (also known as a torch-applied or heat-welded membrane) is a sheet membrane made from modified bitumen. The bitumen is modified with either APP (atactic polypropylene) or SBS (styrene-butadiene-styrene) polymers to improve its flexibility, temperature resistance, and longevity compared to traditional oxidised bitumen.

The membrane is manufactured in rolls, typically 1 metre wide and 8-10 metres long, with a thickness of 3-4 mm. The underside of the membrane is coated with a thicker layer of modified bitumen that is melted during installation using a propane gas torch. As the membrane is unrolled onto the prepared substrate, the molten bitumen bonds the membrane to the surface and to adjacent membrane sheets at the overlaps.

APP vs SBS Modified Bitumen

The two main types of modified bitumen used in torch-on membranes have different properties:

In Sydney’s temperate climate, both APP and SBS membranes perform well. APP membranes are the more common choice for general applications due to their good heat resistance (important on sun-exposed surfaces) and competitive pricing. SBS membranes are preferred where maximum flexibility and cold-temperature performance are required, such as on building facades or in areas subject to significant structural movement.

Where Torch-On Membranes Are Used

Torch-on membranes are primarily used for external waterproofing applications where durability, UV resistance, and the ability to withstand direct weather exposure are important. Common applications in Sydney include:

• Flat roofs and parapet walls — The most traditional application for torch-on membranes. They provide a durable, long-lasting waterproof layer that can withstand decades of Sydney sun and rain.
• Balconies and terraces — Both tiled and exposed balconies benefit from the robust protection of torch-on membranes. The membrane is applied to the concrete or screed surface before tiles or pavers are laid.
• Podium decks — In multi-storey developments, the podium level (above car parks or commercial spaces) requires waterproofing that can support landscaping, paving, and foot traffic above. Torch-on membranes are the standard solution.
• Planter boxes — Built-in planter boxes on balconies and rooftops require waterproofing that can resist root penetration and constant moisture exposure.
• Retaining walls — The external face of below-grade retaining walls is waterproofed to prevent ground moisture from penetrating the structure.
• Car park roofs — Above-ground car park decks exposed to rain require trafficable waterproofing systems, often based on torch-on membranes.

Torch-On Membrane Installation Process

Torch-on membrane installation is a specialist process that requires trained and licensed applicators. At Waterproofing Sydney, our installation process includes:

1. Surface preparation — The concrete or screed substrate must be clean, dry, and free from sharp protrusions, loose material, and contaminants. Any cracks wider than 1 mm must be chased out and filled with a compatible repair mortar. The surface should be smooth but not polished.
2. Primer application — A bituminous primer is applied to the substrate by brush or roller. This primer improves the bond between the torch-on membrane and the substrate. The primer must be allowed to dry completely (typically 2-4 hours) before membrane application.
3. Detail work — Internal and external corners, penetrations, drains, and upturns are detailed first using pre-cut membrane pieces or fabricated corners. These detail areas are the most vulnerable to leaks and require the most skill to execute correctly.
4. Membrane application — The membrane roll is positioned on the prepared surface. Using a propane gas torch, the applicator heats the underside of the membrane while slowly unrolling it, pressing it firmly onto the substrate. The melted bitumen creates a full bond between the membrane and the surface.
5. Overlap sealing — Adjacent membrane sheets must overlap by a minimum of 75-100 mm at side laps and 150 mm at end laps. The overlap area is heated and pressed to create a continuous, watertight seam.
6. Upturn formation — At walls, parapets, and other vertical surfaces, the membrane is turned up to a minimum height of 150 mm above the finished surface level (or higher where required). The top edge is secured with a metal termination bar or sealant.
7. Inspection and testing — The completed membrane is visually inspected for defects, voids, or unsealed areas. Water testing is performed to verify watertightness before any finishes are applied.
8. Protection layer — A protection board or screed is applied over the membrane to protect it from damage during subsequent construction activities (tiling, landscaping, etc.).

Advantages of Torch-On Membranes

Torch-on membranes offer several significant advantages for external waterproofing:

• Proven performance — Torch-on membranes have been used successfully in Australia for over 40 years. Their long track record gives confidence in their reliability.
• Durability — At 3-4 mm thick, torch-on membranes are significantly thicker than liquid-applied membranes (typically 1-1.5 mm). This thickness provides excellent puncture and abrasion resistance.
• UV resistance — Mineral granule or aluminium foil surface finishes provide good UV protection, allowing the membrane to be left exposed without degradation.
• Immediate waterproofing — Unlike liquid membranes that require curing time, a torch-on membrane provides waterproof protection as soon as it is applied and the seams are sealed.
• All-weather application — Torch-on membranes can be applied in a wider range of weather conditions than liquid membranes, including cooler temperatures and higher humidity. The torch provides its own heat for bonding.
• Consistent thickness — Factory manufacturing ensures uniform thickness throughout, eliminating the risk of thin spots that can occur with liquid-applied membranes.
• Long lifespan — Properly installed torch-on membranes last 15 to 25 years in exposed applications, and even longer when protected beneath tiles or pavers.

Limitations and Risks

Torch-on membranes are not suitable for every application, and their installation carries some inherent risks:

• Fire risk — The use of an open flame (gas torch) creates a significant fire risk, particularly on roofs near timber framing, insulation, or other combustible materials. Fire safety precautions are essential and a fire watch period after installation is required.
• Not suitable for internal wet areas — Torch-on membranes are not typically used inside bathrooms due to the fire risk, fumes, and the difficulty of applying them in confined spaces. Liquid membranes are preferred for internal applications.
• Complex geometry challenges — While torch-on membranes handle large flat areas efficiently, they are more difficult to detail around complex penetrations, corners, and irregular shapes compared to liquid membranes.
• Specialist skills required — Torch-on application requires training and experience. Incorrect torch technique (too much or too little heat) can result in poor bonding, charred membrane, or fire.
• Heavy — Torch-on membrane rolls are heavy (25-35 kg per roll), making them difficult to handle on roofs and elevated areas.
• Fumes — Heating bitumen produces fumes that can be unpleasant and potentially hazardous. Adequate ventilation and PPE are required during application.

Torch-On Membrane Costs in Sydney

Torch-on membrane waterproofing costs in Sydney depend on the area size, substrate condition, access difficulty, and membrane specification. Typical price ranges:

• Small residential balcony (5-10 sqm): $1,500 – $3,500
• Medium balcony or terrace (10-25 sqm): $3,000 – $6,000
• Large balcony or roof area (25-50 sqm): $5,000 – $10,000
• Commercial or large roof (50+ sqm): $80 – $150 per sqm

These prices include surface preparation, priming, membrane supply and installation, detail work, and testing. They do not include protection layers, screeding, or tiling. For a precise quote, contact Waterproofing Sydney.

Torch-On vs Liquid Membranes: When to Use Each

The choice between torch-on and liquid membranes depends on the application:

• Use torch-on for: External roofs, large balconies, podium decks, planter boxes, and any exposed application requiring maximum durability and UV resistance.
• Use liquid for: Internal wet areas (bathrooms, laundries), small balconies with complex detailing, areas with many penetrations, and applications where fire risk must be minimised.

For a comprehensive comparison, see our liquid membrane vs sheet membrane guide.

Maintenance and Lifespan

Torch-on membranes require minimal maintenance but benefit from periodic inspection. We recommend:

• Annual visual inspection of exposed membranes for cracks, blisters, or lifting at seams and edges
• Clearing debris and vegetation growth from membrane surfaces and drainage paths
• Checking sealant at termination bars and flashings annually, re-sealing as needed
• Inspecting after severe weather events (hailstorms, high winds) for damage
• Avoiding storing heavy or sharp objects directly on exposed membrane surfaces

With proper installation and maintenance, a torch-on membrane system in Sydney should provide 15-25 years of reliable waterproofing protection.

Compliance and Certification

Torch-on membrane installations in NSW must comply with relevant Australian Standards and building codes. For domestic wet areas, AS 3740-2021 applies. For external and structural waterproofing, the National Construction Code (NCC) and relevant AS standards apply. NSW Fair Trading requires licensed waterproofers for all wet area work, and building certifiers require compliance documentation for structural waterproofing.

At Waterproofing Sydney, all our torch-on membrane installations are carried out by licensed, experienced applicators using products from leading Australian waterproofing brands. We provide full certification and warranties for every project.

Frequently Asked Questions

Can torch-on membrane be used in bathrooms?

Torch-on membranes are not commonly used inside bathrooms due to the fire risk from the open flame, the difficulty of working in confined spaces, and the fumes produced during application. Liquid-applied membranes (acrylic or polyurethane) are the standard choice for internal wet areas. Torch-on membranes are best suited to external applications like balconies, roofs, and podium decks where there is adequate ventilation and minimal fire risk.

How long does a torch-on membrane last?

A properly installed torch-on membrane in Sydney typically lasts 15 to 25 years in exposed applications. When protected beneath tiles, pavers, or a screed, the lifespan can exceed 25 years. The longevity depends on the membrane quality, installation standard, UV exposure level, and whether the membrane is subject to foot traffic or mechanical stress. Regular inspection and maintenance help maximise the lifespan.

Is torch-on waterproofing better than liquid membrane?

Neither is universally better. Each type has strengths suited to different applications. Torch-on membranes excel in large external areas requiring maximum durability and UV resistance. Liquid membranes are superior for internal wet areas, complex geometries, and areas with many penetrations. The best waterproofing solution depends on the specific project requirements. At Waterproofing Sydney, we select the optimal membrane type for each application.

Can torch-on membrane be applied over an old membrane?

In many cases, yes. A new torch-on membrane can be applied over an existing torch-on membrane provided the existing membrane is firmly bonded to the substrate, free from blisters and moisture, and in generally sound condition. This approach avoids the cost and disruption of removing the old membrane. However, the existing membrane must be assessed by a professional to determine if overlay is appropriate. Adding layers increases the total membrane thickness and weight, which may need to be considered structurally.

What safety precautions are needed for torch-on membrane installation?

Torch-on installation requires strict fire safety protocols including removal of combustible materials from the work area, use of fire extinguishers and fire blankets, a fire watch period of at least 2 hours after completing torch work, appropriate PPE (heat-resistant gloves, safety boots, eye protection), and gas cylinder safety procedures. In Sydney, Hot Work Permits may be required depending on the building and local council requirements. Only trained and licensed applicators should undertake torch-on membrane installation.