In 1932 a major storage dam was erected at Butgenbach, close to Malmedy in the province of Liège, Belgium. A wonderful lake was also created. Nowadays the Belgian electricity producer Electrabel owns and operates the 1,8 MW turbine. Some maintenance of the wall was done in the sixties. The lake was partially emptied and the concrete wall was coated with tar based gunnite. Now, 40 years later, a new maintenance is needed. A European tender led rapidly to the final winner, being the Italian-Swiss company CARPI with the Italian converter Sibelon. They are specialized is water repelling maintenance of such constructions. Their technique is always the same : protect the substrate with a PVC geomembrane.

This flexible membrane is 2,5 mm thick, and has a synthetic felt backing facing the concrete. Between concrete and felt, a geodrain structure is laid, being a polyethylene net of some 4 mm thickness. This has to drain the little water in case of small leaks. This will then be drained off through pipes at the bottom of the wall. The horizontal PVC strips of 1 m wide are perfectly stretched using a patented system, which is not easy on the curved, conical walls, and with some 20 meter height. The strips are assembled by a hot air welding system.

This 2,5 million Euro project started more then a year ago, and will be finished in September 2004.  The lake will be filled again with water and fish will be transplanted.

Scaffolding assembling. The dark part of the wall is gunnite	General view of the PVC coated wall