Waterproofing a shower before tiling is not just good practice in New Zealand – it is a legal requirement under the NZ Building Code. Skip this step and you risk serious structural damage, mould, and a very expensive repair bill down the track. Here is everything a homeowner needs to know before starting a shower tiling project.
What the NZ Building Code requires
The NZ Building Code clause E3 (Internal Moisture) sets out the rules for wet areas. It requires that shower enclosures and wet areas are constructed so that water cannot penetrate to building elements that could be damaged by moisture. In practical terms, this means a continuous, compliant waterproof membrane must be applied to walls and floors before any tiles go on. Failing to waterproof correctly can also affect your home insurance and any future LIM reports.
Why tiles alone are not waterproof
This surprises many homeowners: ceramic and porcelain tiles are not waterproof on their own. Water passes through grout joints and, over time, through micro-cracks in grout. Without a membrane beneath, that moisture soaks into the substrate – whether that is a fibre-cement sheet, plasterboard, or a timber framing system – causing rot, mould, and structural failure. BRANZ research consistently shows that failed waterproofing is one of the leading causes of building defects in NZ homes.
What substrates are suitable for shower walls?
Not all wall linings are appropriate behind tiles in a wet area. The most common compliant options are:
- Fibre-cement sheet (e.g. James Hardie's Villaboard) – a popular, moisture-resistant tile backer
- GIB Aqualine – a moisture-resistant plasterboard suitable for wet areas when correctly waterproofed
- Compressed fibre-cement or tile backer boards – rigid and stable
Standard GIB plasterboard (white or pink) is not suitable as a direct tile substrate in a shower, even with waterproofing applied over it.
Choosing a waterproofing membrane
There are two main types of membrane used in NZ showers:
| Type | Examples | Pros | Cons |
|---|---|---|---|
| Liquid-applied membrane | Ardex 8+9, Mapei Mapelastic | Easy to apply, good for complex shapes | Requires correct thickness and cure time |
| Sheet membrane | Schluter Kerdi, fabric-reinforced systems | Consistent thickness, fast | Needs careful lapping and bonding |
Ardex and Mapei are both well-established brands in the NZ trade market. Sika also offers waterproofing systems used by professional tilers. Always follow the manufacturer's data sheet – the number of coats, coverage rate, and cure time are critical to achieving a compliant result.
Where does the membrane need to go?
The membrane must cover:
- The entire shower floor, including into the drain
- All walls within the shower enclosure, typically to a minimum height of 1800 mm (or to the full height of the tiled area)
- All internal corners – reinforced with membrane tape or fabric strip
- Around penetrations such as the drain outlet and any pipe entries
- The floor-to-wall junction – a common failure point if not properly reinforced
Corners and junctions are where most waterproofing failures occur, so take extra care here.
Step-by-step overview for a liquid membrane
- Prepare the substrate – ensure it is clean, dry, flat, and structurally sound. Fix any movement or gaps.
- Prime – apply the manufacturer's recommended primer and allow to cure.
- Tape all corners and joints – embed reinforcing tape or fabric into the first coat of membrane.
- Apply first coat – use a brush or roller to work the membrane into corners and over tape. Allow to cure fully.
- Apply second coat – in the opposite direction to the first. Check the manufacturer's minimum dry film thickness.
- Test before tiling – some professionals do a simple flood test on the shower floor. Allow full cure (often 24–48 hours minimum, longer in cold or humid conditions).
- Tile over the cured membrane – use a suitable tile adhesive rated for wet areas.
DIY or licensed tiler – what can a homeowner do?
Applying waterproofing membrane and tiling are not restricted building work in most residential shower situations, so a competent homeowner can legally do this themselves. However, the work must still comply with the Building Code, and poor application is a common and costly mistake.
If your shower project involves moving or adding plumbing (drain, water supply), that is restricted work under the Plumbers, Gasfitters and Drainlayers Act and must be carried out by a licensed tradesperson registered with the PGDB. Similarly, any electrical work (such as installing a heated towel rail or exhaust fan) must be done by a registered electrician under the EWRB.
When to call a professional
Consider hiring a qualified tiler if:
- You are unsure about substrate suitability or existing damage
- The shower has a complex shape, niche, or linear drain
- There is existing mould or rot that needs assessment
- You want the work to be covered by a professional warranty
- The project is part of a larger bathroom renovation requiring a building consent
A professional tiler will be familiar with compliant systems and can ensure the membrane is applied correctly. You can find experienced, vetted local tilers on tradedirectory.co.nz.
A quick note on safety
Some waterproofing products contain solvents or sensitising agents. Always work in a well-ventilated space, wear gloves and eye protection, and read the safety data sheet (SDS) for any product you use. WorkSafe NZ has guidance on safe handling of construction chemicals.