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Under One Roof

Canadian Roofing Reference Manual

6.2 Rubberized Membrane

The rubberized material is made up of specially selected blends of asphalt, synthetic rubber and mineral stabilizers, modified with additives to promote adhesion. It is a hot applied, rubberized membrane compound designed to provide a joint free membrane when applied to acceptable, well prepared surfaces.

The rubberized membrane is pre-packaged as “cakes” or “pucks” in drums or cardboard boxes. The membrane must be melted in an indirect fired double “air” or “oil” jacketed kettle with a mechanical agitator. Direct fired kettles are not permitted to be used to melt with this type of material. Refer to manufacturer’s instructions on heating instructions and temperature limitations.

Once the material has melted, the membrane is hot applied in several layers. The first layer is evenly applied to a minimum thickness of 2 mm (1/12 in) over horizontal and vertical surfaces. A fabric reinforcing sheet is firmly pressed into this first layer of hot membrane. A second layer of membrane is applied over the reinforcing fabric to a minimum thickness of 3 mm (1/8 in). The entire application provides a continuous monolithic coating.


The kettle should be equipped with a mechanically operated agitator and separate temperature gauges for both the oil bath and the material. The material is placed on the top of the kettle over the oil heating conducting pipe system. Extreme care should be taken to avoid overheating of the material at this stage. That is why a separate gauge is needed to control the temperature of the oil bath. The melting temperature should not exceed 200°C (392°F). Heating the material beyond this maximum temperature will affect the quality of the product and cause it to lose important oils and polymers.

The kettle is filled by melting a few units (pucks) of material at a time and after it has reached a fluid condition, add more material until the kettle is full. During the melting process, the material in the kettle must be continuously stirred by the mechanical agitation. The pouring temperature of the material (temperature of material in the kettle) should be between 180°C to 200°C (356°F to 392°F). Do not overheat the material. The material should be applied as soon as possible after the heating temperature has been reached. Only as much material as can be applied each day should be melted on that day.


The most common application of the rubberized material is over a primed concrete deck. Rubberized material can also be installed over plywood decks and steel decks covered with plywood or gypsum boards. Once the material has been melted and heated to the desired temperature, it is ready to be applied.

The material should be drawn from the kettle, poured and spread onto a dry, clean, primed surface. The material is spread carefully and uniformly by means of squeegees or push brooms in multiple layers with a reinforcing fabric embedded in the first layer. The material can be installed on vertical surfaces, walls, cants or curbs as required.

All cracks in the substrate (roof deck) wider than 3 mm (1/8 in) should receive a minimum application of hot-applied material 3 mm (1/8 in) thick and 300 mm (12 in) wide, and should be reinforced with a butyl or neoprene sheet a minimum of 47 mils thick and 225 mm (9 in) wide centered over the crack. Note that EPDM is incompatible with asphalt, refer to manufacturers instruction to verify compatibility of materials.

When applying membrane over plywood decks, all joints in the deck should receive a minimum application of 3 mm (1/8 in) by 225 mm (9 in) of hot applied material. The material should be reinforced with a spun-bond nylon or polyester sheet, a minimum of 150 mm (6 in) in width centered over the joint, pressed into place, allowed to cool and a second application of hot-applied material poured over top. When applying the membrane over plywood or gypsum boards on a steel deck, the joints in the boards should be treated with a tape before applying the rubberized membrane.

Once the joints have been taped, the application can proceed. A layer of polyester reinforcing material, not less than 1 m (39 in) in width, shall be applied into the still warm material and pressed firmly into place, lapped a minimum of 50 mm (2 in). The reinforcement should be installed in the direction of the gypsum boards longer dimensions. Once cooled, a second layer of rubberized membrane should be applied, completely covering the reinforcement.

If pinholes develop during application of the membrane, it may indicate that the concrete deck requires further curing or that the primer has not been allowed to completely dry. No pinholes or blisters should be left in the finished membrane. Work should stop and the deck and primer should be allowed to dry completely before application of the membrane resumes. The first pour should be a minimum 2 mm (1/12 in) thick with a non- woven polyester sheet embedded into the first pour and completely covered with the second pour with a minimum thickness of 3 mm (1/8 in).

All junctions of horizontal and vertical surfaces and all deck projections should receive membrane flashings.

Once the membrane has been installed, a separation sheet should be installed so the insulation does not stick to the membrane. The separation sheet should be embedded into the membrane while it is still hot. The adjoining sheets should overlap a minimum of 50 mm (2 in).

Rubberized membranes should not be left exposed to the weather or construction traffic. Thermal insulation should be installed to protect the membrane as soon as possible. Never apply a rubberized membrane in direct contact with any coal-tar pitch products.

Roof Edge Detail

A 300 mm (12 in) width of rubberized material should be applied on to the horizontal and 150 mm (6 in) up the vertical using a squeegee or push broom. An elastomeric sheet, such as neoprene or butyl should be set into the still warm material. The elastomeric flashing should have a minimum width of 250 mm (10 in) and have end laps a minimum of 100 mm (4 in). A second pouring of membrane material should be applied over the elastomeric sheet, fully covering the sheet and extending a minimum of 100 mm (4 in) beyond the stripping edges.