Concrete substrate preparation is becoming a compliance-critical part of waterproofing performance.
Waterproofing failures are rarely caused by the membrane alone.
In many cases, the membrane is only the final visible layer in a much broader system. Falls, drainage, joints, hobs, penetrations, substrate condition, concrete defects and workmanship all determine whether the waterproofing will perform over time.
NCC 2025 introduces a stronger system-based approach to water management. For external areas such as concrete roofs, balconies and podiums, the substrate is no longer just a background surface for the waterproofing contractor to work over. It becomes a compliance-critical component of the waterproofing design.
For concrete remediation and construction teams, this is a significant shift.
Key message: before the membrane goes down, the concrete needs to be right.
NSW timing: NSW is scheduled to adopt NCC 2025 on 1 May 2027. Until then, NCC 2022 Amendment 2 remains the current edition in NSW. Always confirm the applicable NCC edition, state variations and transitional arrangements for the specific project.
Waterproofing starts with the concrete
NCC 2025 introduces important changes affecting external waterproofing, including minimum structural falls, substrate requirements, step-downs, hobs, drainage provisions and the location of exposed joints. For relevant external concrete areas, the structural substrate must provide the required fall rather than relying on a screed, topping or tile bed to correct drainage later.
This means the quality, geometry and condition of the concrete slab are directly tied to waterproofing compliance.
A flat slab, back-falling balcony, poorly finished podium, defective hob, cracked substrate or contaminated concrete surface may not simply be a workmanship issue to resolve later. It may compromise the ability of the waterproofing system to comply, drain and perform as intended.
Why this matters
Historically, many external waterproofing problems were addressed during the finishes stage. If the concrete slab was not quite right, falls could often be adjusted using screeds or toppings. While this was common practice, it also introduced risks.
Screeds can crack, debond, retain moisture and conceal defects. They may also complicate leak detection and make future remediation more difficult. Where membranes are installed over non-structural layers, failures in the screed or topping can affect the membrane above it.
NCC 2025 moves the industry toward greater discipline in the original structural substrate and water-management design. The implication for designers, builders and remedial contractors is clear: waterproofing success depends on the concrete being right before the membrane is installed.
The practical impact on concrete works
1. Falls must be achieved in the structural substrate
External areas need to drain effectively. The NCC 2025 provisions introduce a minimum 1:80 fall for relevant external structural substrates, compared with the 1:100 minimum fall commonly referenced in AS 4654.2 for external waterproofing membranes.
This places greater responsibility on concrete set-out, formwork, finishing and quality control. For new works, the required falls need to be formed at the time of placement. For existing buildings, engineers and remedial contractors may need to assess whether the structure can be locally modified, ground, repaired or rebuilt to improve drainage.
2. Membrane-readiness becomes a concrete QA item
A waterproofing contractor cannot deliver a durable result over an unsuitable substrate. Concrete may require grinding, scabbling, patching, crack repair, laitance removal, moisture assessment, surface profiling or contamination removal before membrane application. Surface preparation is part of the waterproofing system, not merely a cosmetic task.
A membrane-ready substrate should typically be sound, clean, dry or suitably conditioned, free from laitance and contaminants, adequately profiled, properly detailed at edges and penetrations, and free from defects that may reflect through or compromise the membrane.
3. Concrete defects can become waterproofing defects
Cracks, honeycombing, spalls, poorly compacted concrete, delaminated repairs, corroding reinforcement and movement joints can all create local weaknesses in the waterproofing system.
In remedial work, it is not enough to cover these issues with a new membrane. The underlying concrete defects should be investigated and treated before waterproofing is reinstated.
This is particularly important on balconies, podiums, terraces, plant decks and roof slabs, where water exposure is continuous and access for future repair is expensive.
4. Hobs, upstands and penetrations need early coordination
NCC 2025 also addresses structural step-downs, hobs and detailing around building elements. These details cannot be treated as late-stage adjustments. They need to be coordinated between the architect, structural engineer, hydraulic engineer, builder, concreter and waterproofing consultant.
Poorly formed hobs, inadequate set-downs, uncoordinated penetrations and late service penetrations through completed slabs are common causes of water ingress. Under the new expectations, these issues are likely to receive greater scrutiny.
5. Drainage upgrades may require controlled core holing
In existing buildings, waterproofing failures are often associated with more than membrane deterioration. Many balconies, podiums, terraces and roof slabs suffer from insufficient drainage capacity, poorly located outlets, ponding, blocked drainage paths or a lack of overflow provisions.
Where drainage is inadequate, remedial works may require new outlets, overflow points, inspection points or service penetrations through the existing concrete structure.
This makes core holing an important part of the waterproofing remediation process. However, core holing for new drainage is not simply a drilling activity. It should be carefully planned, scanned, approved and coordinated with the structural engineer, hydraulic designer and waterproofing consultant.
Before coring, reinforcement, post-tensioning, embedded conduits and services should be located using suitable scanning methods. The proposed penetration should then be reviewed to confirm that it does not compromise structural capacity, reinforcement layout, durability, fire separation, drainage performance or waterproofing continuity.
Once completed, the penetration must be properly detailed. This may include forming falls to the new outlet, repairing exposed concrete, protecting reinforcement, installing compatible drainage fittings, reinstating fire or acoustic requirements where relevant, and integrating the waterproofing membrane into the outlet or overflow detail.
For CARE, this is a key area where concrete works and waterproofing performance intersect. Controlled core holing can allow drainage upgrades to be introduced safely and effectively, provided the works are undertaken with appropriate investigation, execution and QA.
What this means for existing buildings
The new provisions will have the greatest direct impact on new construction and major works once adopted in the relevant jurisdiction. However, they are also likely to influence expectations for remedial work.
Owners, strata managers, engineers and builders may increasingly ask whether existing balconies, terraces and podiums can be upgraded to align with current waterproofing principles.
For existing buildings, this may involve:
- investigation of existing falls and drainage paths;
- review of ponding and overflow provisions;
- concrete condition assessment;
- crack mapping and delamination surveys;
- cover meter and reinforcement corrosion assessment;
- substrate moisture and contamination checks;
- localised concrete repair;
- grinding or reprofiling of concrete surfaces;
- reconstruction of hobs, edges and terminations;
- controlled core holing for new drainage outlets, overflow points or service penetrations;
- preparation of membrane-ready substrates; and
- QA records before waterproofing installation.
In many cases, full alignment with new-build provisions may not be practical without significant reconstruction. However, the same principles still help reduce risk: remove water efficiently, repair the substrate properly, detail transitions carefully, and provide evidence that the surface was suitable before the membrane was applied.
The role of concrete remediation contractors
The waterproofing industry often focuses on membrane selection. That is important, but membrane selection alone does not solve poor substrate design, inadequate drainage or defective concrete.
This is where concrete remediation contractors have a critical role. Specialist concrete teams can assist by preparing the structure before the waterproofing trade arrives. This may include concrete repairs, crack treatment, corrosion remediation, surface grinding, falls correction, localised demolition, edge detailing, substrate preparation, controlled core holing and QA documentation.
CSP defines the level of surface roughness required to achieve proper bonding between the existing concrete and the repair or protective system being applied.
For CARE, this is directly aligned with our core services.
CARE supports engineers, builders and waterproofing consultants by undertaking the concrete investigation, preparation and repair works required to make substrates suitable for long-term waterproofing performance.
Our role may include:
- GPR scanning and cover meter surveys before cutting, coring or intrusive investigation;
- core holing to confirm slab build-up, concrete thickness, falls, screeds, toppings, membranes and concealed waterproofing layers;
- core holing for new drainage outlets, overflow provisions, inspection points or service penetrations where designed and approved by the project engineer;
- concrete condition assessment;
- delamination and drummy concrete identification;
- concrete breakout and patch repair;
- reinforcement cleaning, treatment or replacement;
- crack injection and localised leak sealing;
- substrate grinding and profiling;
- surface preparation for membrane application;
- reinstatement of core holes and penetrations using compatible repair materials and appropriate waterproofing detailing;
- core sampling and laboratory testing coordination;
- photographic QA records; and
- preparation of areas for inspection by engineers or waterproofing consultants.
A shift from “apply a membrane” to “manage water”
The most important message from the NCC 2025 waterproofing changes is that waterproofing is not simply a product. It is a water-management system.
The concrete substrate must drain. The structure must be detailed to receive the membrane. The surface must be prepared. The joints must be coordinated. The hobs, set-downs, outlets, overflows and penetrations must be built correctly. The system must be documented and verifiable.
For the construction industry, this is a positive shift. It encourages earlier coordination, better workmanship and fewer hidden defects.
For building owners, it should lead to more durable outcomes and fewer recurring leaks.
For concrete remediation contractors, it confirms what many failures have already shown in practice: waterproofing performance starts before the membrane.
CARE’s position
CARE helps project teams convert substrate uncertainty into practical site evidence before waterproofing works proceed.
As NCC 2025 places greater emphasis on structural substrates, falls, drainage and membrane readiness, concrete preparation and repair will become increasingly important to waterproofing compliance.
CARE is positioned to support this transition by providing practical, site-based concrete investigation and remediation services that help engineers, builders and waterproofing specialists deliver more reliable outcomes.
Before the membrane goes down, the concrete needs to be right.
And before water can be managed properly, the structure, substrate and drainage pathways need to be understood.
That is where CARE can help.
Sources and project-specific advice
Refer to the ABCB NCC 2025 preview and the NSW Government NCC guidance. NCC application varies by jurisdiction and project. This article is general information and is not a substitute for project-specific advice from the relevant certifier, engineer or waterproofing consultant.
