We used Duram Durapond. We had to do three generous coats, and most crucial of all was to use the mesh between the first and second coat. As it was cast concrete, we had to ensure that all the air bubbles in the concrete had to be filled with the firast coat of waterproofing. Follow the link for instructions on the product.
http://www.duram.co.za/wp-content/uploads/2012/06/Durapond-Datasheet.pdf