Liquid Polyurethane Membrane Provides Seamless Seal For Flat Roof

April 27, 2000
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Planners and roofing companies still face a big challenge in finding an inexpensive, timesaving and durable sealing system for flat roofs on industrial buildings. Particular problems are presented by roofs with complex shapes and a large number of breakthroughs, such as airshafts and pipe supports. It is hard to get around these problems using conventional roof sheeting, especially as it is usually around the breakthroughs that the roof begins to leak.

It was for this reason that Bayer S.p.A. recently used a crack-bridging liquid polyurethane membrane to refurbish the roof of a pharmaceuticals production plant at its site in the Northern Italian town of Garbagnate. The advantages of the polyurethane system are that it is applied in liquid form and cures to yield a seamless membrane with long-term flexibility. It is easy to seal around even the most complex fittings. The weather-stable liquid membrane, based on Bayer’s Desmodur® E raw material, was supplied by Kemper System GmbH & Co. KG of Vellmar, Germany.

The 500-square-meter roof covered with bituminous roof sheets had cracked, and thick folds had formed. In some places, it was leaking. Complete refurbishment was therefore essential. However, the old roof covering did not have to be removed, as the moisture that had penetrated the roof could dry out through the liquid polyurethane membrane. This eliminated the cost of removing and disposing of the old roofing material.

The surface was first steam-cleaned, and all standing water was removed. An adhesion promoter was then applied. The liquid membrane, supplied ready-to-use, was poured onto the roof and spread using rollers. Bayer technician Dr. Ralf Lemmerz said, “Polyester matting is laid in this base coat. This ensures the minimum film thickness required for a long service life, and reinforces the overall system.”

Once the base coat had dried, the topcoat was applied. The moisture-curing system has a total thickness of less than three millimeters. Italian applicators, Vitali, were able to complete the refurbishment work within just 10 days despite poor weather conditions.

Roof-sealing systems based on liquid polyurethane membranes are extremely durable. Samples of a 15-year-old roof membrane from a commercial and residential building in the industrial Ruhr region of Germany were investigated in Bayer’s laboratories. Dr. Lemmerz said, “The tests showed that the membrane was still in perfect condition, despite exposure to UV radiation, weathering and pollution.”

For more information about coating raw materials, contact Bayer AG, phone +49 214 30 61684, fax +49 214 30 66426, visit

For more information about the weather-stable liquid membrane from Kemper System GmbH & Co. KG, phone +49 561 8295 35, fax +49 561 8295 10, visit


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