Articles - Remedial Builders.com

Not every water leak that shows up near a balcony, window or wall is a waterproofing membrane failure. In remedial building work, the team at Remedial Builders sees that one of the most common and most expensive misdiagnoses is treating a leak as a “failed membrane” when the water is actually entering somewhere else entirely, at the junction where two different building materials meet and where the flashing was never detailed correctly in the first place.

This article looks at why intersections between dissimilar materials are such frequent leak points, why these leaks are so often mistaken for waterproofing failures, and how they should have been built, and can be repaired, using sound flashing principles.

Why material intersections leak

Modern facades are assemblies of very different materials: lightweight cladding, Colorbond and other steel roofing, masonry and brickwork, glazing, balustrades, and render. Each material moves differently, has a different surface, and is covered by its own manufacturer’s installation guide. The problem is that the junctions between those materials frequently fall into a grey area, the cladding manufacturer’s guide stops at the edge of the cladding, the roofing guide stops at the edge of the roof, and the Australian Standards give general principles rather than a detail for every possible three-way intersection.

A classic example is a junction where modern wall cladding meets a Colourbond roof which in turn meets a brick balustrade wall. Three materials, three different movement characteristics, and three different “standard” details that were never designed to talk to each other. When the flashing at that intersection is inadequate, under-lapped, reverse-lapped, too short, or simply absent, water finds the path of least resistance and travels inside the building envelope.

The “illusion” of a waterproofing failure

Here is where diagnosis goes wrong. Water that enters at a poorly flashed intersection rarely appears at the point of entry. It runs along framing, falls down a cavity, tracks across a slab, and finally shows up as a damp patch on a ceiling or wall, very often in the proximity of a balcony.

Because the stain is near the balcony, the obvious assumption is that the balcony’s waterproofing membrane has failed. The tiles get pulled up, a new membrane goes down, tens of thousands of dollars are spent, and the leak continues, because the actual entry point was never the balcony floor at all. It was the balustrade connection, the junction of the balustrade to the wall, or the intersection of differing materials beside the balcony.

The lesson for any remedial investigation is to find the true entry point before specifying a repair. Water testing each suspected zone in isolation, balustrade, wall intersection, then balcony floor, will usually reveal that the membrane was never the problem.

Modern cladding walls: the Z flashing and the weep gap

Lightweight cladding systems are one of the most common places this goes wrong. Cladding is not a waterproof barrier on its own, it is the first line of defence in a drained system. Some water will get behind it, and the system has to give that water a way back out. That is the job of the Z flashing.

A correctly detailed cladding base works like this:

A Z flashing is installed at the bottom of the cladding, formed so that it directs any water that is behind the cladding back out to the face.
A deliberate short gap is left at the bottom edge, a weep gap, so water can physically escape rather than being trapped.
Builders’ wrap (the breather membrane) is installed behind the cladding and is lapped so that it overflashes down onto the Z flashing. This is the critical sequence: water on the back face of the cladding runs down the wrap, onto the Z flashing, and out through the weep gap.

Done this way, the wall is a drained and ventilated system. Any breach in the outer skin is harmless because the water has a defined, downhill escape route.

The common mistake: sealing the cladding solid

The most frequent defect we see is the exact opposite of good practice: the cladding is siliconed up entirely, including along the bottom edge. The intention is usually well meant, to “seal it against water”, but the effect is the reverse.

Once the bottom is sealed, the weep gap is gone. Now any breach in the silicone anywhere on the wall, and silicone will eventually fail, crack, or lose adhesion, lets water in with nowhere to escape at the bottom. The wall has been turned from a drained system into a bucket. Water sits behind the cladding against the wrap and framing, and the longer it stays the more damage it does.

The correct repair is to reinstate the drainage path: remove the sealant from the base, confirm or install a properly lapped Z flashing, ensure the builders’ wrap overflashes onto it, and re-establish the weep gap so the wall can drain and breathe again. Sealant should only be used where the design intends it, never as a substitute for flashing.

Air-conditioning supply-air grilles

Another commonly overlooked entry point is the external air-conditioning supply-air grille. These penetrate the facade, and if the opening is not flashed properly behind the grille, they become a direct path for water during wind-driven rain events.

In normal conditions the grille may appear perfectly fine. But in a storm with horizontal, pressure-driven rain, water is forced through the louvres and into the wall cavity around an unflashed penetration. Because it only leaks in those specific conditions, the fault is intermittent and easily blamed on something else nearby. The fix is to flash the penetration correctly, head flashing over the opening, lapped to the wrap, with the grille sitting over the flashing rather than the flashing relying on the grille’s own seal.

The underlying principle

This is not just good trade practice, it reflects how manufacturers and standards intend these systems to perform. At Remedial Builders, every material intersection is detailed to weatherproof the junction independently of sealant, exactly as these systems are designed to work. Metal flashing guides, for example, call for a minimum overlap cover against the cladding (commonly cited as around 150 mm) specifically to resist wind-driven rain, and require flashings to be designed to weatherproof the junction independently of sealant. Manufacturer cladding manuals likewise specify that openings, penetrations and intersections be flashed before the cladding goes on, with the drainage path built in. When a junction leaks, it is almost always because one of these long-established principles was skipped on site.

Across all of these examples, the cladding-to-roof-to-brick intersection, the balustrade, the cladding base, and the supply-air grille, the same principle applies. Flashings, not sealants, are what keep water out. Sealant has a short service life and fails silently. Flashing, correctly lapped so that every layer sheds water onto the one below and ultimately back to the outside, works for the life of the building and does not depend on anyone maintaining a bead of silicone.

When a leak appears, the value of an experienced remedial builder is in resisting the obvious answer. The damp patch near the balcony is a symptom, not a diagnosis. More often than not the cure is not another membrane, it is a properly detailed flashing at the intersection where the leak was quietly starting all along.

If you have a persistent leak that has already had “waterproofing” repairs without success, it is worth having the intersections and flashings investigated before spending again on the membrane. Remedial Builders can diagnose the real source of the leak and repair the flashing detail correctly.

Technical references and further reading

The flashing principles described above are set out in detail in manufacturer installation literature and Australian standards. The following authoritative sources publish the relevant junction and flashing details:

Relevant standards referenced in these guides include AS/NZS 2179.1 (metal rainwater goods and flashings) and AS 3566 (fasteners for external use). Diagrams and full junction details remain on each owner’s site via the links above.

If you own or manage a strata building in Sydney, “concrete cancer” is one of the most important problems to understand early. Left untreated, it can compromise the structural integrity of balconies, car parks, and facades, and the cost of repair climbs steeply the longer it is ignored. This article explains what concrete cancer is, the warning signs to look for, why Sydney’s coastal environment makes it especially common, and the repair options available to your owners corporation.

What Is Concrete Cancer?

Concrete cancer, known technically as concrete spalling, occurs when the steel reinforcement bars inside concrete begin to rust. As the steel corrodes, it expands and pushes against the surrounding concrete, causing it to crack, flake, and break away. Once the process starts, it tends to accelerate, because the exposed steel is then subject to even more moisture and corrosion.

Why Sydney Buildings Are Especially at Risk

Sydney’s coastal climate is a major factor. Salt-laden air along the coast and harbour penetrates concrete over time and speeds up the corrosion of internal steel. Older apartment blocks built in the 1960s through 1990s are particularly vulnerable, as construction standards and waterproofing methods of the era often allowed moisture to reach the reinforcement more easily. Buildings near the ocean, on the harbour, or with exposed balconies and rooftop car parks face the highest risk.

Warning Signs to Look For

Cracking or flaking concrete, particularly on balconies, ceilings of car parks, and external walls
Rust-coloured stains bleeding through concrete or render
Bubbling, drummy, or hollow-sounding render when tapped
Exposed and visibly rusted steel reinforcement
Concrete that crumbles or falls away in chunks

If you notice any of these signs, it is worth arranging a professional inspection promptly. Early intervention is almost always cheaper and less disruptive than emergency repairs after a section of concrete fails.

Repair Options for Strata Buildings

The right approach depends on the severity and extent of the damage. A qualified remedial builder will typically remove the damaged concrete, treat or replace the corroded steel, apply a protective coating to prevent future rusting, and then patch and finish the area to match the surrounding surface. In more advanced cases, additional measures such as cathodic protection may be recommended to halt corrosion across a larger area. A proper diagnosis is essential, because surface patching alone will not stop corrosion that is already underway beneath the surface.

Protect Your Building’s Value and Safety

Concrete cancer is a structural and safety issue as well as a financial one, and it rarely resolves on its own. Acting early protects both the safety of residents and the long-term value of the building. If you suspect concrete cancer in your strata building, our team has been diagnosing and repairing these issues across Sydney since 2008. Contact us for a professional assessment and a clear, honest scope of works.

Water Leaks at Material Intersections: The Hidden Cause Behind “Waterproofing” Failures