Re-waterproofing the basin at the base of La Géode cinema in Cité des Sciences in Paris

Inside this sphere, which looks not unlike the Earth, there is a dizzying cinema theatre with 400 seats on a gradient of 27°. The hemispherical 1000 m² screen is one of the largest in the world and, with a diameter of 26 m, almost fills the whole space.

At the base of the building, there is an approx. 1800 m² metal basin filled with freshwater, built and waterproofed at the same time as the sphere was constructed, and which stages it perfectly. Having served well for almost 30 years, the waterproofing had to be redone. The contracting firm Sertec recommended to the client the only PMMA-based waterproofing system which has obtained DTA certification from the Centre Scientifique et Technique du Bâtiment (CSTB): Triflex ProTect reinforced with special fleece.

Triflex''s Technical Service assessed the site to determine the best way to pre-treat the substrate, which had been waterproofed with a mix of bitumen and polyurethane. To this end, an adhesion test was carried out with Triflex ProTect on the old waterproofing and on the metal substrate.

The horizontal waterproofing was retained, but the old waterproofing on the vertical surfaces was completely removed with a high-pressure sandblaster.

MMA resins were used for all the layers of the new system, making use of two advantages: the methacrylate has extremely short curing times and the overall system has a long life. These full-surface fleece-reinforced waterproofing layers dry within 30 minutes and offer outstanding resistance to static and dynamic loads acting on the substrate. In addition, the system is root- and rhizome-resistant and has a service life of at least 20 years (ETA class W3).

Five workers managed to complete the waterproofing of the approx. 1800 m² surface in record time. In the course of this major project, Sertec came to appreciate the constant technical and commercial support from Triflex France.