Before any tiles, linings, or flooring go over a waterproofing membrane, a proper inspection is essential. In New Zealand, waterproofing in wet areas must meet the requirements of the NZ Building Code — particularly Clause E3 (Internal Moisture) — and skipping or rushing the inspection stage is one of the most common causes of costly leaks and remediation work down the track. Here's what a thorough pre-sign-off inspection should cover.
Why the Inspection Stage Matters
Once tiles or linings are installed over a membrane, any defects are hidden and extremely expensive to fix. A proper inspection — ideally by the waterproofing contractor and, where required, a building inspector — catches problems while they're still accessible. For work requiring a building consent (such as new wet areas in a renovation), your local council will require an inspection before you can cover the membrane. Always confirm inspection requirements with your council before proceeding.
MBIE Building Performance provides guidance on when building consent is required and what inspections are needed at each stage.
Membrane Coverage and Continuity
The inspector should check that the membrane covers all required surfaces without gaps, holidays (missed spots), or thin patches. In a shower or bathroom, this typically means:
- The entire floor area
- Walls to the required height (usually a minimum of 1800 mm in a shower enclosure, though your consent documents may specify more)
- All internal corners and junctions
The membrane must be continuous — any breaks, bubbles, or delamination are a fail.
Membrane Thickness
Most liquid-applied membranes have a minimum dry film thickness (DFT) specified by the manufacturer — commonly 1.0–1.5 mm for wet areas, but always check the product's technical data sheet. Inspectors may use a wet film thickness gauge during application or a DFT gauge after curing to verify this. If the membrane is under-thickness, it may not provide adequate protection regardless of how good it looks.
BRANZ publishes research and good practice guides on wet area waterproofing that outline acceptable thickness standards.
Upstands and Coved Corners
Upstands are where the membrane turns up from the floor onto the wall. These are a critical weak point. The inspection should confirm:
- Upstands meet the minimum height required (typically at least 100 mm above the finished floor level, or higher at shower thresholds)
- Coved (rounded) internal corners have been formed correctly — sharp 90° corners are prone to cracking and membrane failure
- The membrane is bonded firmly at all upstand edges with no lifting or peeling
Flashings and Penetrations
Every penetration through the membrane — drain outlets, pipe penetrations, fixings — is a potential leak point. The inspection should check:
- Drain flanges are correctly integrated with the membrane (not just sitting on top)
- Pipe penetrations are sealed with compatible flashing collars or sealant
- Any pre-formed corners or flashings are correctly lapped and bonded
- No fasteners or fixings have punctured the membrane without being properly sealed
Substrate Preparation and Adhesion
A membrane is only as good as what it's bonded to. The inspector should confirm:
- The substrate (concrete, fibre cement sheet, or GIB Aqualine in wet areas) was correctly prepared and primed
- There is no evidence of delamination or poor adhesion — a tap test (tapping the surface and listening for hollow sounds) can help identify this
- Substrate joints and cracks were reinforced with tape or bandage before membrane application
Falls and Drainage
The floor must have adequate fall to the drain so water doesn't pond. In shower areas, a minimum fall of 1:60 is generally accepted, though steeper is better. The inspector should check:
- Water drains freely to the outlet with no pooling
- The drain is at the lowest point of the shower floor
- The drain cover is correctly fitted and accessible
Curing Time
The membrane must be fully cured before inspection and before any tiles or adhesive are applied. Curing times vary by product and conditions — temperature and humidity both affect cure rates. The inspector should confirm the required curing period (check the manufacturer's data sheet) has elapsed. Applying tiles to an uncured membrane is a common mistake that leads to adhesion failure.
Products from suppliers such as Ardex, Mapei, and Sika all have specific curing requirements — always follow the relevant technical data sheet.
Water Test
For shower trays and wet areas, a flood or water test (also called a ponding test) is best practice and may be required under your consent conditions. This involves:
- Blocking the drain and filling the area with water to a set depth (typically 25–50 mm)
- Leaving it for a minimum period (often 24 hours)
- Checking for any drop in water level or signs of moisture on the underside of the substrate
If the water level drops, there is a leak — the membrane must be investigated and repaired before proceeding.
Documentation
A good waterproofing contractor will provide written sign-off documentation confirming:
- The product used (brand, product name, batch number)
- Application method and number of coats
- Measured or estimated DFT
- Date of application and curing period
- Results of any water test
Keep this documentation — it may be required for your Code Compliance Certificate (CCC) and is valuable if any issues arise later.
When to Call a Professional
Waterproofing in wet areas is specialist work. While some preparatory tasks may be DIY-friendly, the membrane application itself — and certainly the inspection — should involve a qualified waterproofing contractor. For consented work, a licensed building inspector will carry out the formal inspection. You can find qualified local waterproofing professionals on tradedirectory.co.nz. For any plumbing connections to drains or water supply, note that this is restricted work under the Plumbers, Gasfitters, and Drainlayers Act and must be carried out by a licensed tradesperson registered with the PGDB.
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