Hidden Concrete Cancer | Rooftop Membrane Waterproofing Solutions

Our team was called to a project in Caloundra, Queensland where concrete cancer and blowout corrosion were discovered beneath the rooftop membrane system, issues that were also contributing to serious water ingress and mould growth in the top-floor apartment. 

What began as a moisture problem turned into a full-scale structural and waterproofing repair, highlighting the importance of early detection and quality remediation. This blog outlines how we delivered a complete solution through expert concrete cancer repair and rooftop membrane waterproofing.

The Problem: Concrete Cancer & Water Ingress

We started inside the top-floor apartment, where the tenant had reported persistent mould. A closer look at the ceiling revealed several fine cracks, which are clear signs that water had been making its way in from above. These weren’t just surface blemishes; they were active pathways for moisture, feeding mould growth and creating an unhealthy living environment.

From there, we moved up to the rooftop to trace the source. As we removed the perimeter flashings, the real issue became clear, concrete cancer was silently spreading beneath. The reinforcing steel (reo bar) embedded in the concrete had begun to corrode, expanding and causing the concrete to crack and break away. Left untreated, this kind of damage can seriously compromise a building’s structural integrity. It was clear we needed to act fast to stop further deterioration and restore proper waterproofing protection.

Our Solution: A Comprehensive Approach

We provided a detailed scope of works, divided into three main sections to address both the internal and external issues:

Scope of Works 1: Internal Ceiling Injection Works

The first step was to inject the cracks in the apartment ceiling with SNSeal high-pressure injectable sealant to form a water-tight seal.

The process involved:

1. Drilling diameter holes in the ceiling to prepare for injection.
2. Injecting SNSeal high-pressure injectable sealant into the cracks.
3. Activating the injectable sealant with SNSeal activator

Scope of Works 2: Rooftop Membrane Repair & Concrete Cancer Remediation

Once the interior issues were stabilised, our attention turned to the rooftop directly above the affected apartment—specifically over Unit 15, where the water ingress had originated.

We started by stripping back, removing perimeter flashings and grinding off the aged netted membrane to expose the bare rooftop substrate.
That’s when we uncovered a more serious issue: concrete cancer hidden beneath the flashings and along the perimeter, as well as blowout damage at the expansion joint.

Perimeter Flashing & Concrete Cancer Remediation

Upon inspection

We discovered the perimeter flashings were in place, but there was clear evidence of water ingress, mould growth, and areas that had not been adequately membraned. These issues pointed to the need for further inspection and remediation.

Inspection After Flashing Removal

Once the perimeter flashings were removed from the rooftop upturns, we revealed significant concrete cancer beneath. The corroded steel reinforcement (reo bar) was exposed, and the surrounding concrete had deteriorated, compromising the structural integrity.

Remediation Steps:

1. Jackhammered back the damaged concrete around the perimeter edges to remove the affected areas.
2. Exposed and cleaned the corroded steel reinforcement (reo bar), ensuring it was free from debris and contaminants.
3. Mapped out all areas affected by concrete cancer to ensure comprehensive remediation.
4. Rebuilt the damaged sections using T40 grout to restore structural integrity.
5. Applied a primer coat in preparation for the waterproof membrane installation.

Expansion Joint Repair: Concrete Cancer & Blowout Remediation

Scope of Works 3: Full Rooftop Membrane Reinstallation

After completing the concrete cancer remediation and expansion joint repairs, we moved forward with reapplying the waterproofing membrane across the entire rooftop. This critical step ensured lasting protection from water ingress and reinforced the structural integrity of the building:

• Reactivated the existing membrane system to ensure proper adhesion.
• Applied a fresh layer of membrane across the entire rooftop surface.
•  Added two coats of Silcor 75 UV stable topcoat for enhanced durability and protection against the elements, up and over the edges of the rooftop area.

Reapplied the flashings & Works Completed