Balcony slab junction injection across five apartments — Gold Coast–Tweed corridor.

The building

A residential strata building on the Gold Coast–Tweed corridor with balconies across five adjacent apartments sharing a common slab junction line between the balcony slab and the main floor slab.

The problem

The slab junction had failed across all five apartments, allowing water to track through the joint and into the ceilings and walls of the units below. The failure was consistent along the line — a construction joint that had opened over time, not a localised membrane defect in any single balcony.

The approach

Removing the balcony finishes and re-membraning across all five apartments would have been disruptive, slow and costly for an occupied building. We determined the joint could be sealed with PU injection from below, targeting the leak path directly without decanting residents or stripping balconies.

The work

We drilled and installed mechanical packers along the slab junction at regular spacing across the affected bays, then injected hydrophilic resin to stop the active leakage, followed by hydrophobic resin for long-term flexibility. The resin expanded as it cured, filling the joint void. The photo shows the packers in place and the resin going off — the expanded material visible around the packers confirms the joint was fully charged.

The result

The joint was sealed across all five apartments from a single access point below. No balcony finishes were disturbed, and the residents remained in place throughout. The body corporate received a documented record of packer locations and resin types for their building file.