The level of waterproofing that materials provide is typically referred to in geotechnics using a measure of permeability called the k-value. CC has been tested to BS1377 and has an average k value of between 10-8 and 10-9 m/s, which is similar to clay; a range commonly referred to as being impervious.
The permeability of a CC lined structure can be adjusted by selecting an appropriate method for joining the material. Please see the CC User Guide: Jointing and Fixing document for more information.
If the overall impermeability is critical for your application, we would recommend the use of our CC Hydro™ material, which incorporates a high-performance containment geomembrane that is thermally welded with testable joints for quality assured containment applications. Please see the CC Hydro Brochure for more information.