Waterproofing questions, answered

AS 3740 — Waterproofing of Domestic Wet Areas — is the Australian Standard that prescribes minimum requirements for waterproofing in residential bathrooms, ensuites, laundries, toilets and other wet areas. It applies to all domestic wet-area construction in Australia, including new builds and renovations.

Under the National Construction Code (NCC), compliance is required for new residential construction and renovation involving wet areas. In Queensland, waterproofing of wet areas is a regulated activity — it must be carried out by a QBCC-licensed waterproofer, and a written inspection certificate must be provided.

If you are renovating a bathroom or replacing wet-area finishes, the membrane must be inspected and certified before tiling proceeds. Tiling over an existing membrane without inspection and certification is not compliant.

A waterproofing membrane is a purpose-designed barrier — liquid-applied or sheet form — applied beneath tiles to the structural substrate. It prevents water from penetrating the substrate. A tile sealer is applied to the tile and grout surface to reduce staining and surface moisture absorption.

A tile sealer does not waterproof the substrate beneath the tiles. Many people believe their tiled bathroom is waterproof because the tiles are sealed — this is not the case. The membrane beneath the tiles performs the waterproofing function.

In Queensland, waterproofing of wet areas is a regulated construction activity under the QBCC Act. It must be carried out by a licensed waterproofer. Unlicensed waterproofing cannot be certified, may invalidate building insurance and creates liability issues at resale. DIY waterproofing is not legally permissible for wet areas in Queensland residential properties.

Written warranties typically reflect the system type, substrate condition and application scope. As a general guide:

*Manufacturer system warranties of up to twenty years may be available on qualifying projects. Always ask for a written warranty before works commence — verbal warranties are difficult to enforce. At Innovare Waterproofing, we provide written warranties on every installation.

Yes. For commercial, strata and body corporate clients with significant waterproofing assets, we can arrange periodic inspection and maintenance programmes — identifying early-stage deterioration in joints, flashings and membrane surfaces before failures develop. Proactive maintenance significantly extends service life and reduces lifecycle costs.

First, document the leak — photographs, date and description. Then contact the contractor who carried out the work, in writing, requesting they inspect and address the defect under their warranty obligations.

If you have no written warranty or the contractor is unresponsive, contact the QBCC — they have a dispute resolution process for waterproofing defects in Queensland. If you would like an independent assessment to support a warranty or QBCC claim, we can provide a written inspection report.

Costs vary significantly with application type, substrate condition, access requirements and system specification. It is not possible to provide reliable ballpark figures without a site inspection. As a general orientation:

• Bathroom membrane (new installation): cost reflects the area waterproofed, system selected and substrate preparation required.
• Balcony remedial waterproofing: preparation costs (tile removal and disposal, substrate repair) often exceed the membrane application cost itself.
• Commercial and large-scale projects: quoted on a project-specific basis after investigation.

We provide transparent, itemised written quotations following site inspection. We do not quote without inspecting.

Cure times vary with product, temperature and humidity. Liquid-applied polyurethane and acrylic membranes under typical SEQ conditions (20–30°C, moderate humidity) are generally ready for tiling in 24–48 hours after the final coat. In cooler or high-humidity conditions, curing may take longer. Tiling before the membrane has fully cured can cause adhesion failure.

Common indicators of waterproofing failure include:

• Water staining, mould or moisture on walls, ceilings or floors adjacent to or below wet areas
• Tiles or flooring that sound hollow, are delaminating or have grout cracking
• Musty odours in rooms adjacent to bathrooms, balconies or roofs
• Rust staining or concrete spalling on balcony soffits or edges
• Visible damp patches at the base of external walls (potential rising damp)
• Ponding water on balconies or rooftops

If you observe any of these signs, call us for an assessment on 0488 773 232.

The most common causes are:

• Incorrect membrane selection — the wrong membrane type for the application.
• Inadequate substrate preparation — applying to dusty, damp or weakly bonded substrates.
• Insufficient membrane thickness — applying below-specification coverage rates.
• Poor detailing — inadequate treatment of corners, penetrations, flashings and drains.
• Missing reinforcement — corners and stress points require fabric reinforcement.
• Applying over movement — a rigid membrane across active structural movement.
• UV exposure — a non-UV-stable membrane exposed to Queensland UV without protection.

Yes. We apply waterproofing systems to pools, spas, water features, tanks and water-retaining structures using products specifically rated for water contact and, where required, potable water contact. Not all membranes are suitable for permanent immersion — system selection for these applications requires specific product knowledge.