There are a number of reasons why balconies leak. It can range from construction mistakes—such as an inadequate waterproofing system during the initial build—to external factors that gradually compromise the integrity of the waterproofing membrane. Over time, exposure to weather conditions, structural movement, and drainage issues can all contribute to balcony leaks, making timely maintenance and repairs essential.

1. Balcony Membrane Failure

A waterproofing membrane plays a crucial role in keeping your balcony dry by acting as a barrier to prevent water from seeping into the structure. Over time, however, these membranes can degrade, leading to cracks and separations that allow moisture to infiltrate. If left unchecked, this can cause significant damage.

Ponding water and poor drainage may contribute to this deterioration, particularly if the membrane is not designed for prolonged exposure to water. Addressing these issues early can help maintain the integrity of your balcony’s waterproofing system.

Some common reasons why membranes fail include:

• Thermal changes – Balcony materials expand and contract with temperature fluctuations, which can create breaches in the membrane.
• Poor surface preparation – A lack of proper surface preparation can lead to poor adhesion of the waterproofing system.
• Incompatible primer and membrane selection — Failure to properly prime surfaces or using an incompatible combination of primer and waterproofing membrane can compromise the system’s effectiveness.
• Poor subsurface or sub-tile drainage — When drainage isn’t adequate, constant moisture can saturate tiling or topping screeds, causing water to pool and accelerating membrane deterioration.
• Ponding water — If there are dips or low points on the balcony surface or around drains, and it takes more than two days for the water to drain or evaporate, prolonged saturation can wear down the waterproofing system and cause further damage.

2. Broken or Cracked Surfaces

Concrete spalling resulting from water leaking through from the balcony above.

Cracks in concrete, tiles, grout, breached protective coatings, and waterproofing defects can create openings for water to enter a structure. This moisture exposure may eventually contribute to steel corrosion and concrete deterioration if not properly managed. Even small cracks have the potential to let water seep in gradually, leading to progressive deterioration.

Spalling concrete, aka concrete cancer, shows rusting steel on a balcony edge.

When water enters a crack, it can start a process that may lead to the oxidisation/rusting of the reinforcing steel (reo). Over time, this corrosion can weaken the steel bars, potentially impacting the concrete’s durability and, in some cases, its load-bearing capacity. Could small cracks be exposing your structure to hidden risks?

Moisture readings from the grout lines reveal high moisture content levels after many days of dry weather, indicating potential long-term water retention issues.

Did you know that materials like concrete, some tiles, and grout are naturally porous? Some tiles, such as terracotta and natural stone, tend to absorb more water than others due to their composition and surface texture. These materials can absorb water without a proper sealer, which may eventually compromise the structure. Applying a quality sealant repels water and enhances their resistance to wet weather.

4. Structural Movement and Expansion Joints

Popping balcony tiles due to the lack of expansion joints.

All buildings expand and contract due to temperature changes and moisture exposure. Without adequate expansion joints, stress builds up in the structure, leading to cracks in the membrane and tiled surfaces. The joints should be installed every 3 meters and around the balcony’s perimeter to decrease the risk of popping tiles – and breaking the adhesive and waterproof membrane. These joints allow controlled movement, reducing the risk of damage caused by thermal fluctuations.

5. Efflorescence, Leaching and Moisture Damage

Efflorescence on tile grout is caused by moisture drawn up from the tile bed and depositing salts and minerals as the water evaporates.

Have you ever noticed white, salty chalky marks on concrete or masonry surfaces? That’s likely efflorescence. The powdery deposit itself doesn’t significantly weaken the material, but its presence indicates underlying moisture issues that could cause damage over time. Addressing efflorescence requires identifying the source of moisture, which could be from leaks, poor drainage, rising damp, or improper construction practices.

6. Poor Drainage and Ponding Water

This balcony is experiencing significant leaching from the edge. In this case, the drip edges were not installed to the Australian Standard. They were placed after the completion of the tiling, which caused water to be trapped in the bedding.

As mentioned further up, balconies are ideally designed to channel water away from the surface with proper falls. If water pools due to poor drainage, it may contribute to the breakdown of waterproofing materials over time. Blocked drains, inadequate slopes, or incorrect balcony design can be factors in this issue.

Soaking wet subsurface of a tiled balcony where waterproofing membrane is submerged in water over a long period because of drainage issues.

Waterproofing failures can sometimes be linked to improper installation. Contractors lacking experience may apply and detail waterproofing systems incorrectly, fail to account for drainage falls and building movement, or rush the process to cut costs. Over time, these mistakes can lead to expensive repairs and serious structural issues.

At Waterstop Solutions, we hold industry-recognised licences and certifications, including QBCC for waterproofing and concreting, NSW builder’s licence, and Cm3 prequalification. Our qualifications in working at heights and confined spaces allow us to handle a range of remedial waterproofing and concrete repair challenges safely and effectively. Learn more about our Licences, Certifications and Industry Qualifications here.

Why Addressing Waterproofing Issues Early is Essential

It’s easy to delay repairs, especially when a leak seems minor. But waiting can make the problem much worse. Here’s why taking action early is essential:

• Structural Integrity at Risk – Water can weaken concrete, corrode reinforcement, and compromise the stability of the balcony and adjoining structures.
• Mould and Health Issues – Persistent moisture promotes mould growth, affecting indoor air quality and posing health risks.
• Increased Repair Costs – A simple repair today can prevent expensive remediation work in the future.
• Legal and Insurance Issues – Delays in repairs can lead to disputes with property owners, neighbours, or tenants and may impact insurance claims.

Are you wondering what the actual cost of delayed building maintenance could amount to if maintenance and repairs are deferred?

The following blog article may help you find some answers. This blog delves into the escalating costs, safety risks, and property value implications of postponed waterproofing and concrete repairs. Read more here.