Basement Water Ingress Remediation – 8 Storey Apartment Development, Sutherland Shire
Project Type: New 8-storey apartment development
Location: Sutherland Shire, NSW
Client: Head Contractor
Challenge: Significant water ingress through shotcrete joints, anchors, wall/slab junctions and cracks
Repair Method: Penetron System + Hydrophobic Injection
Scope: 90m of Penetron treatment, 35 shotcrete anchors, 15m wall/slab junction remediation
Outcome: Active water ingress reduced from running and pressurised leaks to minor dampness or dry conditions during rainfall events
Project Overview
TruBond Concrete Repairs was engaged by the head contractor to remediate significant water ingress throughout the three-level basement of a newly constructed eight-storey apartment development in Sydney's Sutherland Shire.
The basement structure was constructed using shotcrete retaining walls, a common wet-wall system where minor moisture migration can be expected. However, the volume of water entering the structure exceeded acceptable levels, with active leaks observed through shotcrete construction joints, shotcrete anchors, wall/slab junctions and isolated cracks within the basement structure.
During periods of heavy rainfall, water ingress ranged from minor seepage through to running water and, in some locations, pressurised water jetting from the wall.
The objective of the remediation works was to significantly reduce active water ingress and assist the contractor in achieving acceptable waterproofing performance throughout the basement structure.
The Challenge
Water ingress was present across multiple basement levels and manifested through several different pathways.
The most significant leaks were observed through:
Shotcrete construction joints
Shotcrete anchor locations
Wall/slab junctions within basement stairwells
Localised cracks within in-situ concrete walls
Like many deep basement excavations, the structure was subject to substantial hydrostatic pressure generated by groundwater and stormwater accumulation behind the retaining walls.
While waterproofing measures had been incorporated during construction, several pathways remained that allowed water to track through the structure and discharge internally during rainfall events.
The challenge was not simply stopping isolated leaks, but systematically identifying and treating numerous ingress points across the basement while accommodating the ongoing pressures acting behind the retaining walls.
Remediation Strategy
Following inspection and assessment of the affected areas, a combined remediation approach was adopted using the Penetron System and targeted hydrophobic injection.
Penetron System
The Penetron System formed the primary method of remediation throughout the project.
Approximately 90 lineal metres of leaking shotcrete joints and cracks were treated, along with 35 active shotcrete anchor locations and approximately 15 metres of leaking wall/slab junctions.
The remediation process involved:
Identifying and exposing active water ingress pathways.
Stopping active water flow using Peneplug where required.
Rebuilding and sealing the repair areas with Penecrete Mortar.
Applying a Penetron crystalline waterproofing coating to create a permanent waterproofing barrier within the concrete matrix.
Unlike traditional surface coatings, Penetron works by forming insoluble crystals within the concrete's capillary structure. These crystals react in the presence of moisture and continue to develop within the concrete, helping to block water pathways while remaining integrated with the substrate.
This system was particularly well suited to the project due to the number of active leaks present throughout the basement and the inability to access the positive side of the structure.
Hydrophobic Injection
In addition to the Penetron works, hydrophobic resin injection was utilised to address several leaking hairline cracks within in-situ concrete walls on Basement Level 3.
These cracks were associated with localised waterproofing failures and allowed groundwater to migrate through the structure.
Hydrophobic injection was selected as it reacts with water to form a durable closed-cell foam capable of sealing active water pathways and preventing further ingress through the crack.
The combination of crystalline waterproofing and targeted injection allowed each leak mechanism to be addressed using the most appropriate remediation method.
Project Outcome
The remediation works delivered a substantial improvement in basement waterproofing performance.
Areas that had previously exhibited running water, continuous streaming leaks and pressurised water discharge were reduced to either minor dampness or completely dry conditions during subsequent rainfall events.
The project successfully demonstrated the effectiveness of combining crystalline waterproofing technologies with targeted injection techniques to address complex water ingress issues within below-ground structures.
Construction Insights & Lessons Learned
Every remediation project provides valuable insight into how future water ingress issues can be avoided during construction.
The following observations were made throughout the course of this project.
1. Bentonite Waterproofing Systems Must Be Protected During Installation
Where bentonite blankets are used as a primary waterproofing measure, quality control during installation is critical.
Any punctures, tears, weak points or incomplete detailing can create pathways for groundwater migration once hydrostatic pressure develops behind the structure.
Where practical, bentonite blankets should be extended as high as possible up retaining walls to maximise protection.
On this project, Basement Level 3 generally remained relatively dry, indicating that the bentonite system was performing effectively in many areas. However, during significant rainfall events, groundwater was observed migrating to higher basement levels where hydrostatic pressure and drainage limitations contributed to widespread water ingress.
2. Subsoil Drainage Is Critical
Subsoil drainage is often the most important defence against long-term water ingress.
Its primary role is to relieve hydrostatic pressure before water has the opportunity to act against retaining walls and construction joints.
Where drainage systems are undersized, blocked or unable to accommodate peak groundwater flows, even well-designed waterproofing systems can become overwhelmed.
Design consultants should be made fully aware of anticipated groundwater conditions during the design phase, allowing sufficient redundancy and fail-safe measures to be incorporated where necessary.
3. Waterstops Should Be Incorporated Wherever Possible
Construction joints remain one of the most common pathways for water ingress within basement structures.
Where practical, waterstops should be incorporated at wall/floor junctions and other critical construction joints to significantly reduce the likelihood of future leakage.
The cost of incorporating these systems during construction is often minimal compared with the cost of remediation once the structure is complete.
4. Dowelled Connections Require Special Attention
One of the most challenging aspects of this project involved water ingress associated with stair landing connections dowelled into shotcrete retaining walls.
During heavy rainfall events, significant water ingress was observed discharging through the interface between the slab and shotcrete wall.
Investigation indicated that water was tracking from behind the retaining wall, following reinforcement and emerging through the construction joint.
Several measures could assist in mitigating this type of issue on future projects, including:
Installation of waterstops above and below dowelled reinforcement.
Improved subsoil drainage behind retaining walls.
Application of cementitious negative-pressure waterproofing systems to shotcrete surfaces prior to pouring adjoining slabs.
When combined, these measures can significantly reduce the likelihood of water tracking through these complex construction details.
5. Spoon Drains Need Adequate Capacity and Falls
Perimeter spoon drains can play a critical role in managing groundwater entering the lowest basement level.
In our experience, these systems operate most effectively when a minimum 50mm step-down is incorporated between the surrounding slab and the drain itself.
On this project, limited step-down and insufficient falls to drainage points reduced the effectiveness of the system and contributed to overflow during periods of elevated groundwater flow.
Adequate hydraulic capacity should always be considered when designing drainage systems intended to manage groundwater within deep basement structures.
Need Help With Basement Water Ingress?
TruBond Concrete Repairs specialises in water ingress remediation, leak sealing, crystalline waterproofing systems, crack injection and concrete repair solutions across Sydney.
If your project is experiencing active leaks, groundwater ingress or waterproofing failures within below-ground structures, contact our team to discuss a tailored remediation strategy.