Constructed in 1975, the Windermere Apartments have provided high-quality apartment living in Takapuna for almost 50 years. The apartments feature a sub penthouse suite on the second to top floor with large paved terraces with views to Lake Pupuke and the Gulf Harbour. When minor leaks were discovered in the terraces during work to the apartment below, the owners decided to replace the almost 50-year old membrane — an expectedly straightforward project, until the terrace paving was removed… 

As the original membrane detailed was Butynol, Fat Parrot Architecture had previously contacted ARDEX for the project, originally with a brief for a lightweight undertile waterproofing solution. They developed a plan to use ARDEX UD150 — a thin, mesh-reinforced plastic drainage mat used directly under adhered tiled surfaces — on a thin screed bed.

“The original finish was concrete pavers approximately 40mm thick, and the drawings detailed the supporting slabs to be laid to falls,” explains Graeme Fanselow, Director, Fat Parrot Architecture. “But when the pavers were uplifted it was discovered that the slabs had in fact been laid level, with the pavers set on non-continuous beds of mortar under just their corners to create the falls — not a full mortar screed.” 

At this point, a new approach was required, with the key limitations being weight — which couldn’t exceed what was installed previously, and the height of the parapet — which the homeowners did not want increased. This effectively ruled out the possibility of using a chair deck system for the new tiles, so a direct fix system on a new substrate built to the required falls was needed.

This created new challenges for the project as any new solution would need to create the fall required, while still maintaining the original height and weight. The ARDEX team worked with Fat Parrot to find a system that would resolve all issues. “ARDEX were very helpful,” says Graeme. “As things weren’t what was expected, they arranged site meetings when needed to work together and sort out the situation.” 

Different build-up options were considered before they reached the final solution. “The lightweight grouts were still proving to be too heavy so we then investigated their polystyrene base — we were able to work with them on minimum thicknesses of different grouts, how thick the base could be, and whether that was going to be too much weight — we ended up right on the limit. That lightweight construction underneath allowed us to build the falls we required.”

The final build-up features a custom combination of ARDEX products. ARDEX K12 screed and ARDEX A 48 Rapid Screed unbonded have been applied above the concrete slab, with ARDEX WPM 1000 membrane installed on top. ARDEX WPM 002 liquid membrane was also used over flashing on the parapet upstand. The originally specified ARDEX UD 150 mesh-reinforced plastic drainage mat was then applied. Featuring a 6mm drainage channel, the mat allows free passage of water underneath the tiled surface to speed up drying after rainfall. ARDEX X 18 tile adhesive, ARDEX FG 8 Grout and ARDEX Grout Booster complete the installation to form a compliant build-up for the direct-fixed tiles above. 

The system was installed over a 300m² area by Best Skills Limited, an applicator trained by ARDEX to ensure reliability across both specification and installation. The final system is completely unique to ARDEX and enabled them to achieve below minimal threshold requirements. 

The highly bespoke system developed for the project highlights the flexibility of ARDEX’s systems, and the technical support and problem-solving expertise the ARDEX team bring to each project. “ARDEX were excellent,” says Graeme. “They gave us good technical support and have been very helpful.”