Providing the Britomart project with durable waterproofing solutions

Waterproofing a concrete structure that sits only about 100m from the sea and 6 meters below sea level creates a challenge - a challenge that Waterproofing Systems Ltd was able to address with their Rawmat bentonite membrane system.

How does Bentonite work?

Bentonite is a natural clay formed from volcanic ash which can swell to form an impermeable mass, preventing the passage of liquid. Natural sodium bentonite clay will absorb water and expand up to 16 times its dry volume when in contact with water. When confined, e.g. between the ground and the floor slab, the tendency to swell generates substantial swell pressures, preventing the passage of water

When correctly installed, the Rawmat/Rawseal acts as an effective hydrostatic seal. An important factor affecting the amount of swell achieved, is the quality of water hydrating the bentonite. The significant advantage of the pre-hydrated system is that the initial hydration occurs under factory-controlled conditions.

Why Bentonite for Britomart?

  • The Britomart site was a wet site - other products were not suitable for this project.
    Being so far below sea level, it was almost impossible to provide the sufficiently dry substrate required by other products or systems. Given the construction programme, and the hydrostatic pressures on site, these other systems would not have performed to the same level as the pre-hydrated bentonite system.
  • A variety of substrates were required
    In much of the tunnel it was possible to install the waterproofing system directly to the building substrate. For much of the tunnel the pre-hydrated bentonite was installed to the excavated clay. Bentonite is one of the few products that can be installed on a variety of substrates including rock face, concrete and sacrificial steel shutters.
  • A non weather-dependent solution was necessary to keep the project timeline on track
    The programme for construction of the tunnel was very tight. Much of the waterproofing was scheduled for the winter months, which would have been a problem with conventional waterproofing systems. No weather-related "down time" occurred during the bentonite installation.

late 2001

Waterproofing Systems Ltd begins supplying the Rawmat pre-hydrated bentonite to the Britomart main tunnel.

early 2002

Beca Carter, Jasmax and Downer Engineering are impressed by the Waterproofing Systems product range and applicator. Additional contracts are awarded for work on the basement, roof and parapets of the Central Post Office.

late 2002

Waterproofing Systems secures the Concourse Tunnel using Rawmat/Rawseal.

early 2003

The project continues to grow. Waterproofing Systems commences work on the Streetscapes contract using Polyflame, Rawmat and a variety of Gripset Liquid membranes.

Central Post Office Roof Restoration

Perforated base sheet/Glasflame 2mm/Polyflame 4mm sand/Sunguard

The existing roof was comprised of an asphalt sheet membrane, covered in a concrete screed and pavers. The roof area of 1080m2 required complete renovation. The pavers/screed was removed and substrate repairs were completed. A perforated base sheet was installed followed by the Glasflame 2mm/Polyflame 4mm torch-on system. A Sunguard UV coat was then applied. Eterno roof vents were also installed to allow moisture to escape for the concrete substrate.

Central Post Office Roof Parapets

Gripset 51/Gripset RD

The CPO roof has a 1.8 metre high parapet around the perimeter which had previously been waterproofed with an asphalt sheet. This old membrane was removed and the parapets were cleaned. Gripset 51 bitumenous rubber membrane was used as a primer, onto which the Gripset RD acrylic membrane was applied. Gripset RD is a flexible elastomeric liquid membrane designed to waterproof a variety of external and exposed surfaces, and provides a maximum long term protection by forming a tough durable film.

The beginning of Britomart

LBP Certified Applicator getting the job done

The Britomart project was challenging right from the start. We had to show that our product was superior and that is had more advantages over other specified products. We felt confident that Waterproofing Systems would always be a strong contender, but is was not always straightforward and one or two issues had to be overcome.
This was probably the most demanding waterproofing job in New Zealand for the past 10 years, so I feel confident that we can address the requirements of any other project coming up in the future.

John Stallard, Director, Waterproofing Systems