Torch-on uses sheets of modified-bitumen membrane — bitumen reinforced with a polymer (APP or SBS) and a carrier — that are rolled out and bonded to a primed surface by heating the underside with a gas torch so it melts and sticks down. Seams are overlapped and torched so the whole roof becomes one continuous, bonded membrane.
The membrane comes in plain and mineral-finished grades; a mineral or protective finish, or an over-coating, is used where the membrane is exposed to sun so UV does not degrade it over time.
Torch-on suits flat and low-pitch concrete slab roofs, box gutters and concrete balconies — surfaces that are rigid, can take a bonded sheet, and sometimes hold standing water. Because it is bonded across the whole area and is robust underfoot, it handles ponding and light foot traffic better than a thin coating.
It is a membrane system, not a cosmetic coating: it addresses the waterproofing layer itself rather than just sealing the surface.
The surface is cleaned, any failed material removed, and the substrate primed and allowed to dry — preparation is what decides whether the system lasts. The membrane is then torched down with continuous overlaps, and corners, upstands, outlets and penetrations are detailed with extra layers so the vulnerable points stay watertight.
Torch-on is hot work: it uses an open flame, so it is carried out by trained applicators with the right fire precautions. That also means it is not suitable everywhere — see below.
On pitched tiled and metal roofs, torch-on is generally not appropriate — those roofs shed water by overlap and flashing and need repair, not a bonded membrane poured over them. A moving metal roof also flexes too much for a rigid torch-on sheet.
Where open flame is a risk (near combustible materials, timber structures or in tight spaces), a self-adhesive membrane or a reinforced liquid system is safer. Complex shapes, lots of penetrations or detailing-heavy areas are often better served by a liquid-applied system. We assess the roof and recommend accordingly rather than defaulting to one method.