Wet area pre-tile waterproofing inspection in Australia

What it is

The wet area pre-tile inspection is a hold point that happens after the waterproofing membrane is applied and cured, but before the tile bedding starts. The inspector verifies that the substrate, the membrane and the geometry meet AS 3740 Waterproofing of Domestic Wet Areas and, for external transitions like balconies and terraces, AS 4654.2 Waterproofing for external above-ground use. The inspection is mandatory in Victoria under VBA stage requirements and is a recommended hold point in NSW, Queensland, WA, SA, Tasmania, the ACT and the NT.

Once tiles are laid, the only way to confirm the membrane is intact is destructive testing. Pre-tile is the last opportunity to identify failures that would otherwise turn into rectification claims under the six-year statutory home warranty period.

What the inspector checks

Substrate preparation

The substrate must be sound, clean, dry and free of contaminants. Cementitious substrates need a moisture reading typically below 5 percent by mass, verified with a calibrated moisture meter against the membrane manufacturer's data sheet. Compressed fibre cement sheet substrates need joints stopped and corners filleted with a bond breaker behind the angle. Particleboard and standard plasterboard are not permitted in shower enclosures under AS 3740.

Falls

AS 3740 requires the shower floor to fall to the waste at not less than 1 in 100 (1 percent) and not more than 1 in 80 (1.25 percent) within the shower enclosure. The inspector uses a digital level on multiple lines from the perimeter to the waste to confirm consistent fall and no birdbaths. Water in the broader bathroom must drain to the floor waste or shower waste, not pond against the threshold.

Hob heights

Where the shower is hobbed, the membrane must turn up the hob a minimum 25 mm above the highest finished floor level outside the shower. For a stepdown shower without a hob, the highest finished floor level inside the shower must sit at least 25 mm below the floor level outside. Walls in the shower zone are waterproofed to a minimum 1800 mm above the finished floor level, and to the ceiling where the shower head is over 1700 mm.

Membrane coverage

The membrane must extend over the entire shower floor, up walls to the required height, over and behind any hob, around the waste flange and over bond breakers at all internal corners. Penetrations for the waste, tap bodies and mixer bodies must be sealed with the manufacturer's specified flange or sealant. Membrane thickness is checked against the data sheet, typically two coats of liquid-applied membrane delivering 0.5 mm to 1 mm dry film thickness.

Bond breakers and movement joints

Internal corners need a bond breaker tape or fillet under the membrane so it can flex with substrate movement without splitting. Movement joints in the substrate must be carried through the membrane and the tile bed using a flexible sealant joint, not grouted.

Flood test

For showers, AS 3740 supports a 24 hour flood test where the area is filled with water to a depth not exceeding the hob height, with leak inspection through the ceiling below for upper-storey applications. The inspector records start time, water depth, end time and any visible loss.

Common defects flagged on site

• Bond breaker missing at one internal corner.
• Fall in the shower under 1 percent or birdbathing visible on the level test.
• Membrane stopping short of 25 mm above the highest external floor level on the hob.
• Plasterboard used in the shower enclosure instead of a waterproof-rated substrate.
• Waste flange not sealed to the membrane.
• Wall membrane applied less than 1800 mm high.
• Movement joint grouted over with rigid tile bedding.
• Membrane data sheet missing for the system used.

A TradeLens scan picks up the documentary side: missing waterproofer licence (mandatory in QLD and NSW for any work over $3,300), missing membrane data sheet, no flood test record.

Sign-off documentation

• Waterproofer Certificate of Compliance or Form 16 (QLD), signed and dated by the licensed waterproofer.
• Membrane manufacturer data sheet and batch number, retained for warranty.
• Photographic record covering substrate prep, bond breakers, primer coat, membrane coats and flood test.
• Building surveyor or principal certifier inspection sign-off where mandated by the state.

State variations: in Queensland the QBCC requires a licensed waterproofer for any wet area work over $3,300 and a Form 16 is mandatory. In NSW the work is restricted to a Waterproofing licence under Fair Trading. In Victoria registration with the VBA is required for waterproofing trades. The hold-point principle is consistent: no tile bedding until the membrane is signed off.