The level of waterproofing that materials provide is typically referred to in geotechnics using a measure of impermeability 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.

If the overall impermeability level is critical for your application then you will need to carefully consider the CC jointing method you use. Please see the CC User Guide: Jointing and Fixing document for more information.