In the construction world, mass and thickness always inspire confidence. While a liquid waterproofing coating applied with a roller leaves a crust barely one millimetre thick, a quality bitumen membrane reaches 4 to 5 millimetres thick!
This enormous layer of material is why bitumen membranes remain the No.1 choice for heavy-duty waterproofing, especially on rooftops where water ponds.
A modern bitumen membrane is not just tar. It's a high-tech "sandwich":
At the centre there is a mesh (usually polyester or fibreglass) giving the membrane enormous tear resistance. Fibreglass doesn't stretch (stability), while polyester is extremely elastic (follows the building's thermal movements).
The black material surrounding the reinforcement. It's enriched with polymers (plastics or elastomers) so it doesn't melt in summer or crack in winter.
The top surface is covered with a protective layer, usually slate granules in various colours or aluminium foil, which shields the bitumen from destructive UV radiation.
When you go to buy bitumen membrane, you'll see these two acronyms. The difference between them is enormous:
Bitumen blended with elastic polymers (rubber). Incredibly elastic - can be stretched without tearing. Withstands polar cold (down to -20°C) without cracking. Ideal for regions with harsh winters (e.g. Northern Greece) or for metal roofs that vibrate.
Bitumen blended with plastic polymers. More rigid, but with extraordinary heat resistance (won't melt even at 100°C). The ideal, durable choice for the scorching rooftops of Southern Greece (Athens, Crete, Islands).
Bitumen membrane should never be applied directly on bare, dusty concrete. If the contractor simply unrolls the membrane and starts torching, send them away!
The roof is thoroughly cleaned and entirely coated with a black, liquid primer. This penetrates the concrete pores and creates the "bridge" onto which the roll will bond.
The roll features a thin film on its underside. The technician heats the bottom with a propane blowtorch until the film melts and the bitumen becomes like liquid honey, then immediately presses it onto the primed surface.
Rolls are not placed side by side. Each roll must "straddle" the previous one by 10 centimetres . This joint must be torched and pressed with a trowel so well that a small "ribbon" of melted bitumen seeps out at the edge. If water finds even a tiny hole in this joint, it will creep underneath and the waterproofing will be destroyed!
It's October and we want to beat the rains. We buy bitumen membranes to waterproof our flat roof.
The contractor is in a rush. No primer "because the concrete is clean". He buys cheap membranes weighing 3 kg per m². He torches the joints hastily. By the second winter the joints open. Water gets under the sheets, ponds, and seeps through to the living-room ceiling. The roof is full of "blisters".
We pressure-wash, apply a solvent-based primer and wait 24 hours to dry. We buy heavy-duty membrane 4.5 kg/m² (APP) with polyester reinforcement and white slate. The installer torches the 10 cm overlaps slowly and carefully. Around the parapets he turns the membrane 15 cm up the wall. The result is a seamless, impenetrable "basin". The home is safe for the next 15-20 years.
The Final Conclusion: Bitumen membranes remain the toughest and most reliable waterproofing solution, provided you choose the right weight/reinforcement and the joints are flawlessly executed. Don't skimp on material: below 4 kg/m² and polyester reinforcement, you're throwing your money away!
Return to category.
Go to categoryReturn to the central guide.
Go to guide
