Bathroom waterproofing: a homeowner's planning guide

Treat waterproofing as a complete system

Ask the contractor to explain the proposed substrate, preparation, membrane, junction details and compatible finishes as a coordinated system.

The correct specification depends on the room, building and products, so it should be resolved by the qualified people responsible for the work.

This guide helps you prepare questions and collect records; it isn't an installation specification.

Ask which requirements apply

Have the contractor identify the applicable NCC and AS 3740 requirements, the edition being used and the manufacturer's installation instructions for the selected system.

The ABCB's waterproofing guidance is a starting reference, while the project's compliance pathway and design need professional confirmation.

Keep the answer with the drawings so changes to the shower arrangement, floor or fixtures are reviewed against the same design.

Official guidance: ABCB: waterproofing in houses.

Compare systems by suitability

Liquid-applied, sheet and combined systems have different preparation, detailing and compatibility requirements.

Ask why the proposed system suits the substrate and room rather than choosing solely by the product name or price.

Request the product documentation, the installer's details and a clear description of what will be recorded before tiling conceals the work.

Coat count isn't the whole specification

A universal number of coats doesn't describe the requirements of every waterproofing product.

Ask the installer how the selected manufacturer's required coverage, thickness, curing and detailing will be achieved and checked.

Leave the method to the qualified installer and request a documented system rather than judging a membrane only by how many applications you can see.

Upper floors and apartments

Have the designer assess the floor construction, drainage and transitions for the proposed room.

In an apartment, coordinate the work with strata approval and the building's requirements before construction starts.

Ask how penetrations, junctions and the bathroom entry are addressed in the specification, and which checks or completion records are required.

If moisture appears outside the wet area

Record the location and timing of the moisture, photographs and any relationship with shower or bath use.

Arrange an assessment by the appropriate licensed trade, because plumbing, seals, ventilation and waterproofing can involve different investigations.

For an immediate electrical or structural safety concern, keep the area clear and seek urgent professional help.

Use the findings to agree a repair scope before committing to cosmetic replacement of the visible finishes.

What to request at handover

• The selected waterproofing system and relevant product documentation.
• Installer details and available installation records.
• Photographs or other agreed evidence before the area was tiled.
• Relevant completion certificates or inspection records for the project.
• First-use, maintenance and warranty information.