Technical writing for the people who buy remedial work.

When a balcony or bathroom leaks, the membrane gets the blame. It's the wrong defendant. In the large majority of failures we're called to investigate, the membrane did roughly what it was asked to do — it was set up to fail by what happened before and around it.

Three things decide whether waterproofing survives, and none of them is the membrane itself.

Substrate. A membrane is only as sound as what it's bonded to. Lay a quality membrane over a contaminated, dusty, cracked or still-curing substrate and it will debond, blister or tear at the weak point. The failure looks like a membrane failure. It's a preparation failure.

Falls. Water has to leave. If the screed doesn't fall correctly to the drainage point — or worse, ponds in the wrong direction — water sits on the membrane indefinitely, finds the smallest imperfection, and exploits it. No membrane on the market is rated to be permanently submerged in a puddle it was never meant to hold.

Terminations and detailing. Leaks live at the edges, not the field. Up-turns at walls, penetrations for pipes and drains, door thresholds, movement joints — these are where the system either continues unbroken or doesn't. A perfect membrane across the flat area, terminated badly at a single penetration, leaks exactly as much as a bad membrane.

This is why a quote that goes straight to "we'll re-waterproof it" should make an owners corporation nervous. It treats the symptom and ignores the cause — which means the new membrane inherits the same bad falls and the same bad detail, and fails again inside the warranty period. The committee pays twice.

The correct sequence is diagnosis first. Establish why water is getting in — substrate, falls, terminations, or some combination — then specify a system, to the engineer's requirements, that addresses the actual cause. Install it strictly to the manufacturer's specification so the system warranty genuinely attaches, and witness a flood test before anything is tiled over. Document the falls, the batch numbers and the flood test result, so the repair is verifiable and the warranty is enforceable.

A membrane is a component. Waterproofing is a system. The failures we see are almost always system failures dressed up as component failures — and they're avoidable when the work starts with a diagnosis instead of a quote.

"Concrete cancer" is one phrase covering several different conditions, and they don't share a cure. Treating them as one — patching wherever you can see a stain — is how a building ends up with the same spalling reappearing two metres from last year's repair.

The proper name is concrete spalling: the reinforcing steel inside the concrete corrodes, the rust expands to several times the volume of the original steel, and that pressure cracks and blows off the concrete cover. You see the symptom — cracking, rust staining, lumps of concrete dropping off a soffit or balcony edge. The cause is happening out of sight, inside the slab. And there is more than one cause.

Carbonation. Over decades, atmospheric carbon dioxide penetrates the concrete and lowers its pH. Concrete normally protects embedded steel through high alkalinity; as carbonation advances and that alkalinity drops, the steel loses its protective layer and begins to corrode. This tends to be widespread and relatively shallow.

Chloride attack. Chlorides — from a marine environment, or historically from certain admixtures — reach the steel and break down its protection locally and aggressively. Chloride-driven corrosion is often more concentrated and more serious than carbonation, and it doesn't stop just because you've patched the visible damage.

Post-tensioned slabs are a category of their own. These contain tensioned steel tendons under enormous load. Cutting or coring into a post-tensioned slab without knowing exactly where the tendons run is genuinely dangerous and can compromise the structure. This is never exploratory guesswork.

Because the causes differ, so do the treatments — and you can't choose the treatment until you know which cause you're dealing with. That requires testing before cutting: mapping the affected areas, testing for carbonation depth (a simple phenolphthalein indicator shows how far the protective alkalinity has been lost), testing for chloride content, and surveying the extent of delamination rather than just the visible damage.

This is why one honest assessment of concrete cancer should cost a survey, not a guessed figure off a photo. A number quoted without testing is a number quoted without knowing the disease. The defensible approach is to test first, scope the repair with the engineer to the correct treatment for the actual cause, and document every patch with batch records the certifier will accept — so the repair is both correct and provable.

Spalling that keeps coming back isn't bad luck. It's almost always a repair that treated the stain instead of the cause.

If your building is a class 2 building — broadly, residential apartment buildings — the rules around who can legally do design and building work on it changed significantly, and owners corporations now carry obligations they may not realise they have.

The Design and Building Practitioners regime was introduced in NSW in response to a series of high-profile defect failures in apartment buildings. Its purpose is simple to state: make the people who design and build class 2 buildings accountable, registered, and on the record. For remedial work, that has practical consequences a strata committee should understand before engaging anyone.

Practitioners must be registered. Design and building work within the scope of the regime must be carried out by registered practitioners. When you engage a builder for in-scope remedial work on a class 2 building, their registration status is not a nicety — it's a legal precondition. A committee should be able to verify it on the public register.

Declarations get lodged. The regime is built around declarations that the design and the building work comply with the Building Code and relevant standards. These are lodged through the State's lodgement system rather than kept in a drawer. The point is a documented, declared chain of compliance — not verbal assurances.

The owners corporation keeps the evidence. Records, declarations and compliance documentation associated with the work form part of the building's compliance history. An owners corporation that doesn't retain this material can find itself unable to demonstrate that past work was done compliantly — which matters at sale, at insurance renewal, and if a future defect dispute arises.

There's a duty of care behind it. The regime also strengthened the duty owed to owners — including subsequent owners — in relation to building work, widening who can be held responsible for economic loss from defective work.

The practical takeaway for a committee is this: the cheapest quote from an unregistered operator isn't a saving, it's a liability. If the practitioner isn't registered and the declarations aren't lodged, the work may be non-compliant on paper regardless of how it looks on site — and the owners corporation, not the builder, is left holding that gap.

A properly run remedial job treats the compliance trail as part of the deliverable: registered practitioner, declarations lodged, evidence handed to the owners corporation at completion. That paperwork is the difference between a repair you can prove and a repair you merely hope was done right.

Note: regulator and lodgement-portal names in NSW are evolving — verify the current names before relying on this article for compliance correspondence.