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PVC roofing membranes and durability

PVC membranes in use for over 50 years Easy to process and durable

PVC membranes were first employed in outdoor applications in 1950. PVC roofing membranes represent an inexpensive solution and one with a positive ecological profile.

The basic properties of plastics make them the obvious choice for use on flat roofs. These properties include high tensile strength, high elongation at break, low stiffness, high tenacity, high resistance to water and many aggressive media, easy to process, and a tight and smooth surface.

PVC membranes were used for the first time at the beginning of the Fifties. To give German industry watertight and secure roofing quickly and inexpensively, these roofing membranes were designed for the special requirements of industrial roofs and for cost-effective laying.

In the mid-Seventies, PVC membranes were developed further for mechanical fastening on lightweight roof structures. The growing market for large new halls demanded a membrane type that was compatible with the possible vibrations of the supporting structure and had the necessary elasticity: This gave rise to the birth of fabric-reinforced PVC membranes for quick and inexpensive mechanical fastening.

The advantage of mechanical fastening is that the spot and linear fastening of the roofing membranes permits compensation for movement. In addition, the membranes' permeability combined with this laying method prevents the formation of Blisters.

Alongside the success story of monomer-plasticized PVC membranes, which were calendered, the polymeric, extruded PVC membrane was developed in the Sixties. This was prompted by the demand for a flexible, bitumen-compatible waterproofing membrane resistant to many aggressive media such as mineral oil and fatty acids. The bitumen-compatibility demanded specifically in modernization projects and neutrality towards insulating materials was now available even without a separating layer. Another benefit of these membranes is that they are sufficiently permeable for damp roof layers to dry out reliably after renovation.

Thanks to their resistance to many media, it was possible to apply these roofing and waterproofing membranes in the factory with a cold self-adhesive film. Cold self-adhesive polymer roofing membranes have been on the market since the Nineties. They are excellently suited for the renovation of old bituminous roofs and in all applications where the bonding of all roof layers is demanded.

Strict compliance with DIN and EN

In the material standards, limits are given for the composition of roofing membranes. For PVC-P membranes that are not compatible with bitumen, the following composition is demanded:

min. 50 % PVC max. 50 % plasticizer min. 1 % stabilizers max. 16 % additives and pigments

By varying the type and quantity of the included components, it is possible to adapt PVC to virtually any demanded flexibility and softness.

Unlike the production processes in the early years of PVC roofing membranes, today's formulations are precisely adhered to by computer-controlled metering units, thus ensuring constant quality throughout. In addition, the mixing process has also been improved considerably in the intervening years. The consequence of this is that the ingredients today are mixed more smoothly and the formulations remain resistant to weathering for a long time.

The environment-friendly stabilizers used today are responsible above all for UV and weathering resistance. As a result of the constant and critical further development of the membrane material, heavy metals like lead and cadmium were eliminated long ago as stabilizers from PVC-P roofing membranes. Today other metal stabilizers are employed, e.g. calcium and zinc.

Risks and side-effects?

In the early years, PVC-P membranes were mainly only 0.8 to 1.0 mm thick. What's more, the zero-slope roof was standard, whereas today it is very much the exception. It soon became apparent that thinner membranes are unsuitable for more intricate shapes, particularly with hot-air welding under construction site conditions. The minimum thickness was therefore universally increased to 1.2 mm at the beginning of the Eighties. For the reliable production of seams, junctions and penetrations, a minimum thickness of 1.2 mm (and better still, 1.5 mm) is recommended.

Today, the manufacturers' product ranges usually comprise 1.2, 1.5, 1.8 and 2.4 mm thick membranes. Every millimetre of extra thickness enhances the membrane's durability. In terms of sales figures, 1.5 mm membrane is well ahead of the field. At the same time, extruded membranes up to 3.0 mm thick are also available.

The fully exposed roofing membrane has been in used now for over 50 years. This variant accounts for about 70-80% of all flat roofs laid with PVC membranes. If correctly fitted, roof surfaces protected in this way remain functional and usually flawless for decades. Their high-grade formulations ensure a long membrane life - which can easily be 25 years and more.