First establish which building element is being waterproofed

The NCC distinguishes wet areas in buildings from external waterproofing. For houses, its guidance allows relevant wet-area construction paths under Volume Two and the Housing Provisions; external roof terraces and balconies above internal space involve separate provisions referencing AS 4654.1 and AS 4654.2. Class of building, state adoption and the actual element must be checked by the project designer. AS/NZS 4858 addresses membrane performance testing for wet areas; it is not a substitute for the design and installation rules.

Map the exposure to an ALKA pathway

ALKA’s waterproofing range includes ALKA TEN, the polyurethane membranes ALKA 310, ALKA 311 and ALKA 312, along with primers and specialist sprayed systems. The product pages describe possible uses; the project’s substrate, exposure and current TDS determine the final selection.

• Under-tile wet area: assess the chosen membrane’s current wet-area documentation, approved primer, reinforcement and detail system. Verify compatibility with the actual screed, tile adhesive, grout, sealant and substrate. A tile finish does not replace the membrane.
• Balcony or exposed deck: consider an external membrane assembly and an approved wearing surface. ALKA-917 Deck-Proof is ALKA’s trafficable balcony/deck system concept, but its exact layer schedule should be confirmed in writing before specification.
• Roof: determine whether the membrane remains exposed, requires a protective top layer, or sits beneath a different roof finish. Check weather and UV suitability, planned access and roof drainage for the selected assembly. A roof that remains wet after rain needs drainage design, not just another coat.
• Primer choice: ALKA 305 is presented as a polyurethane primer for suitable concrete. ALKA Damp and ALKA Prime T appear in the range, but are not interchangeable defaults. Select the primer after measuring substrate condition and obtaining the membrane maker’s compatible build.

Most failures begin at a detail, not in the middle of a slab

Falls and drainage

Map where water can collect and how it reaches outlets without crossing a threshold. Confirm the outlet body and flange can be integrated into the membrane, and that the final surface still drains after finishes are installed. The required falls and overflow strategy come from the applicable building design, not a generic coating thickness.

Junctions, movement and penetrations

Show the membrane’s path up walls and over hobs, its termination at door frames, corners, parapets and edges, and its connection to pipes and drains. Movement joints need a compatible flexible detail rather than a rigid coat across the gap. Plan for reinforcement or bond-breaker tape where the approved system requires it. The drawings should identify who installs each part when waterproofing meets glazing, cladding, plumbing or tiling.

Substrate and weather

Identify whether the substrate is concrete, screed, masonry, sheet material, a prior membrane or a mixed construction. Check structural stability, contamination, curing compounds and measured moisture; repair unsound areas before coating. Specify preparation and primer for that substrate. Ambient temperature, rain, condensation, substrate temperature and dew point can affect application. Protect the membrane between coats and until it is ready for the next trade.

Finish and access

A tiled bathroom, a tiled balcony and an exposed pedestrian deck need different finishing arrangements. Ask whether tile adhesive bonds to the cured membrane, whether a protective wearing coat is required, and how slip resistance will be assessed in use. Plan access for future inspection and maintenance; even an exposed membrane needs periodic checks at outlets and terminations.

Set a complete system schedule and verify the work

1. Survey and document: classify the building and element; inspect falls, drainage, movement, thresholds, existing leaks and substrate moisture. Agree whether the work is new construction or remedial.
2. Specify every layer: substrate repairs, primer, membrane, detail reinforcement, required application build, cure/recoat windows, protective finish, tile/adhesive compatibility and any access restrictions, all against current ALKA documents.
3. Inspect critical stages: substrate acceptance, completed joints and penetrations, membrane continuity and coverage, details before they are concealed, and the finished assembly. Record batch numbers and site conditions.
4. Agree testing and handover: any water or flood test must follow the designer’s method, timing and building constraints. Photograph concealed work and give the owner maintenance instructions for outlets, sealants and traffic wear.

A membrane cannot correct a structural crack, an inaccessible outlet or a threshold without sufficient space for an appropriate detail. Resolve those conditions in design before promising a waterproof result.

Frequently asked questions

Can the same membrane go in a bathroom and on a roof?

Possibly, if the current product evidence and approved assembly cover both uses. The building detail, exposure, protection and code pathway still differ.

Is a directly foot-trafficable membrane suitable for a car park?

No vehicle rating should be inferred from pedestrian access. Vehicle duty needs a separately approved traffic deck build, wearing layer and design for braking and turning loads.

Can a new membrane be painted over an old one?

Only after identifying the old system, testing bond and compatibility, and resolving trapped moisture or ongoing leaks. Complete removal is often necessary where the old coating is unsound.