The two systems in one paragraph each
Torch-on membrane is a modified bitumen sheet, 3 to 4 millimetres thick over two layers, melted onto the substrate with a propane torch so it fuses to the surface and every overlap welds into the next. It's waterproof the moment it cools, walkable, and rated for 20+ years.
Liquid membrane is polyurethane, acrylic or cementitious coating rolled or trowelled on wet, curing into a seamless film around 1 to 2 millimetres thick. It follows complex shapes easily, needs no flame, and is the standard for internal wet areas like bathrooms and showers.
Head to head
- Thickness. Torch-on's thickness comes off the roll, so it's the same everywhere. Liquid thickness depends on the hand applying it, and most liquid failures are simply coats applied too thin.
- Seams. Torch-on seams are heat-welded; done properly the seam is stronger than the sheet. Liquid has no seams, which is its genuine advantage on complex details.
- Cure time and weather. Torch-on is waterproof as soon as it cools. Liquid needs hours to days between coats and a dry weather window, and rain during cure ruins it.
- Durability and traffic. Mineral-finished torch-on takes foot traffic, trades and ladders. Liquid needs a protective layer or it wears through.
- Movement and heat. Torch-on is engineered for thermal cycling, which is why it's the default in hot climates from Malta to Western Sydney. Liquids vary widely; some crack at joints under repeated movement.
- Lifespan. Torch-on installed to spec: 20+ years. Liquid, well applied: roughly 7 to 15 depending on product, exposure and traffic.
- Cost. Torch-on costs more up front. Over the life of the building it's usually the cheaper system, because you install it once.
- Skill. Torch-on demands a trained hand and hot-works discipline. That's the honest weakness: a bad torch-on install is a bad install. Liquid is more forgiving to apply and less forgiving over time.
Where torch-on wins
Exposed flat roofs, box gutters, balconies and terraces, podium decks, planter boxes, basements and retaining walls, and anything trafficable. Anywhere durability, thickness and weather resistance decide whether the job lasts.
Where liquid wins
Bathrooms, showers and laundries. Highly complex detailing where sheet can't follow the shape. Some overlay situations on existing sound membranes. Internal wet areas are not our trade, and if that's your job we'll say so and point you to a good wet-area waterproofer.
What we actually do
We install two-layer torch-on systems from six manufacturers, to their full specification, and use liquid membranes only as part of a torch-on system where a detail calls for it. If you've been quoted liquid on an exposed roof or balcony, get a second opinion before you sign. If you've been quoted torch-on in your bathroom, get a second opinion on that too.
