Torch-On vs Liquid Waterproofing: Which Is Right for Your Roof?

Reading time: ~6 min

Torch-on and liquid rubber are the two most commonly specified waterproofing systems for flat and concrete roofs in Pretoria. Both systems can provide excellent waterproofing performance when applied correctly. The important part is understanding that they are designed for different situations.

Using the wrong system on the wrong roof can lead to premature failure, higher long-term costs, difficult repairs later, and unnecessary installation complexity. Pretoria's climate — with intense UV radiation, high summer temperatures, rapid temperature swings, and heavy thunderstorm rainfall — places significant pressure on waterproofing systems. That means choosing the correct system matters from the beginning.

What Is Torch-On Waterproofing?

Torch-on waterproofing uses modified bitumen membrane sheets that bond directly to the roof surface using heat. The underside of the membrane contains a heat-activated adhesive layer. During installation, a propane torch melts this layer so the membrane fuses permanently to the primed substrate.

How the System Works

Most torch-on systems include a base membrane layer, a reinforced cap sheet, polyester or fibreglass reinforcement, and UV-resistant surface finishes. The membrane forms a continuous waterproof barrier across the roof surface.

Why Torch-On Is Popular in South Africa

Torch-on membranes perform especially well on flat concrete roofs because they handle standing water effectively, resist UV exposure well, tolerate thermal movement, and deliver long service life. Most quality systems installed correctly last around 15–20 years.

Main Advantages of Torch-On

Strong Long-Term Durability

Torch-on remains one of the most proven waterproofing systems in South African conditions.

Excellent UV Resistance

Cap sheets usually include mineral granules or aluminium reflective coatings that protect the bitumen from direct UV degradation.

Good Resistance to Ponding Water

Torch-on systems generally perform better under standing water conditions than many coating systems.

Main Limitations of Torch-On

Open Flame Application

Because installation requires a propane torch, extra caution is necessary near timber structures, thatch, combustible insulation, and electrical installations.

Less Flexible on Complex Roof Shapes

Torch-on works best on simple, accessible surfaces. Highly detailed roofs with many protrusions can become labour-intensive to waterproof properly using sheet membranes.

What Is Liquid Rubber Waterproofing?

Liquid waterproofing systems are applied as a fluid coating that cures into a seamless waterproof membrane. These systems may include polyurethane membranes, modified bitumen emulsions, or acrylic-modified rubber coatings. The product is typically applied using brushes, rollers, or spray systems. No open flame is required.

How Liquid Waterproofing Works

Once cured, the membrane forms a continuous flexible waterproof layer that conforms to the shape of the roof. Because the system is seamless, it adapts well to curves, corners, penetrations, uneven surfaces, and complex detailing areas. This flexibility is one of its biggest advantages.

Main Advantages of Liquid Waterproofing

• Excellent for complex roofs: works very well where sheet membranes become difficult to install cleanly
• No open flame: safer around combustible materials
• Seamless application: no overlaps or welded seams reduce potential weak points
• Easier detail work: conforms easily around pipes, vents, air-conditioning penetrations, and drain outlets

Main Limitations of Liquid Waterproofing

• Lifespan depends heavily on product quality: premium polyurethane systems perform very differently from low-cost acrylic-based coatings
• Thickness consistency matters: uneven application thickness can reduce durability significantly
• Generally shorter lifespan than torch-on: most quality liquid systems last around 10–15 years

Torch-On vs Liquid Rubber: Side-by-Side Comparison

When Should You Choose Torch-On Waterproofing?

Torch-on is usually the stronger choice when durability and long-term lifespan are the main priorities.

Best Applications for Torch-On

• Large flat concrete roofs: simple flat roof layouts are ideal for membrane systems
• Roofs with good drainage: torch-on performs best when water drains correctly and ponding is limited
• Parking decks and screed roofs: the reinforced membrane handles movement and exposure well
• Long-term waterproofing projects: for owners planning to stay long-term, torch-on often delivers better lifetime value

Where Torch-On Works Especially Well

Torch-on is commonly used on concrete slab roofs, commercial buildings, apartment blocks, parapet wall tops, box gutters, and accessible roof decks.

When Should You Choose Liquid Waterproofing?

Liquid systems become more practical where roofs are complicated or difficult to sheet properly.

Best Applications for Liquid Waterproofing

• Complex roof shapes: roofs with multiple levels, angles, and transitions benefit from seamless application
• High penetration density: liquid systems handle pipes, vents, cable penetrations, and roof equipment more easily than sheet membranes
• Areas near combustible materials: no flame means safer installation around timber framing, thatch sections, and insulated roof systems

Other Common Uses

Liquid waterproofing also works well for balconies, tiled wet areas, shower waterproofing, small inaccessible sections, and existing membrane overlays.

Which Waterproofing System Is Better?

Neither system is universally "better." The correct choice depends on roof layout, surface condition, drainage quality, access, fire risk, budget, and long-term expectations.

For large flat roofs in Pretoria, torch-on membrane is usually the more durable long-term solution — its resistance to UV exposure, ponding water, and thermal movement makes it particularly effective on large concrete roofs.

For detailed or complex roof areas, liquid waterproofing often provides better coverage and flexibility. In many cases, contractors use both systems on different sections of the same property — torch-on on the main slab roof and liquid membrane around difficult penetrations and detailing areas. See also: best waterproofing for flat roofs in South Africa.

Final Thoughts

Choosing between torch-on and liquid waterproofing is not about finding a universally "better" product. It is about matching the right system to the specific roof.

Torch-on generally delivers longer lifespan and stronger performance on straightforward flat concrete roofs. Liquid waterproofing offers better flexibility for complex detailing and sensitive areas where torching is unsuitable.

The most important factors remain proper roof inspection, correct surface preparation, drainage quality, and experienced installation. Even the best waterproofing product fails early if applied incorrectly.