Tiled wet areas and balconies waterproofing system
A bonded waterproofing build for bathrooms, showers and tiled balconies, with the waterproofing layer protected by the final tiled assembly. Exterior balconies require their own drainage, edge and movement-joint design even when tiled.
Where this system fits
A bonded waterproofing build for bathrooms, showers and tiled balconies, with the waterproofing layer protected by the final tiled assembly. Exterior balconies require their own drainage, edge and movement-joint design even when tiled.
Design boundary: A balcony is an external element even when tiles cover its membrane. Confirm the external waterproofing design, compatible adhesive and detail treatment for the actual project.
Layer build and schematic
Layer schematic
Read top to bottom. Not to scale; final thicknesses and details follow the project schedule.
| Element | Specification consideration |
|---|---|
| Intended finish | Tiled. Do not treat tile or grout as the waterproofing layer. |
| Substrate | Sound concrete or specifically approved substrate; confirm moisture, surface profile and repair materials. |
| Membrane | Two coats ALKA 312. Its product page lists 0.68 L/m² per coat for 1.2 mm total DFT; verify the current TDS and actual site consumption. |
| Tiling | Specify an adhesive that ALKA and the adhesive manufacturer confirm as compatible with the cured membrane, together with tile format and service exposure. |
The illustration shows the membrane stack, not the full architectural detail. The designer must coordinate substrate, falls, drainage, joints, thresholds, penetrations, surface finish and interface with other trades.
Specification and application
Design the whole wet-area assembly
Bathrooms and showers need the waterproofed zones, waterstops, puddle flanges, penetrations, vertical returns and transitions shown on drawings. External tiled balconies also need designed falls to drainage, thresholds, edge flashings and movement joints. AS 3740/NCC wet-area provisions and AS 4654 external provisions apply where relevant to the building class and location; this layer schedule alone is not proof of compliance.
Prepare and detail before coating
Check concrete soundness and moisture, remove laitance and contamination, repair voids and form falls before priming. Prime with one coat of ALKA 305 only on a substrate and within conditions accepted by its current TDS. Treat internal corners, pipe penetrations, outlets, wall-floor junctions and movement joints with the specified reinforcement, bond breaker or proprietary detail. Do not bridge a moving joint with a rigid tile finish.
Apply, inspect and tile
Apply two full ALKA 312 coats, observing the specified recoat window, application conditions and coverage. Measure and record wet film coverage or use the specified method to verify total dry film build; inspect continuity at details. Protect the membrane during curing and subsequent trades. Tile only after cure and adhesive compatibility are confirmed. The tile installer remains responsible for adhesive, grout, movement joints and finish details.
Hold points for the specifier
Record substrate acceptance, falls and drainage, primer application, each membrane coat, detail photographs, membrane thickness or consumption, cure, any required water test, and a signed handover before tiling. Decide who owns each inspection and repair if the membrane is damaged by later trades.
Inspection and handover checklist
- Record substrate, moisture and surface preparation acceptance before priming.
- Agree details for junctions, drains, penetrations, upstands and movement joints before broad-area application.
- Verify each layer, coverage, thickness, recoat window and any system-specific testing against the approved method.
- Photograph hold points and document repairs, batch numbers, cure and protection before following trades or traffic.
- Provide the owner with the final layer schedule, inspection records and maintenance or renewal instructions.
Waterproofing performance depends on the whole assembly, not a layer count alone. Confirm the exact approved system in writing for the project.
Product and design references
- ALKA 305 product information and available technical documents
- ALKA 312 product information and available technical documents
- NCC wet area waterproofing requirements — for applicable internal wet areas.
- NCC external waterproofing provisions — for applicable external above-ground areas.
Confirm the current NCC edition and jurisdiction, AS 3740 / AS 4654 where relevant, and the approved ALKA TDS/SDS. The schematic describes a system concept, not a complete certified construction detail.
Need the full project detail?
Send plans, substrate, area, drainage, exposure and finish to ALKA for an appropriate layer schedule and compatibility review.