A leaking shower might seem like a minor nuisance, but left untreated it can cause serious structural damage, mould growth, and even undermine your home's framing and subfloor. In New Zealand's varied climate — from the humid north to the damp south — moisture management in wet areas is critical. Understanding what's causing the leak is the first step to fixing it properly.
Why Leaking Showers Are Such a Big Deal in NZ
The NZ Building Code requires wet areas like showers to be waterproofed to prevent moisture penetrating walls and floors (refer to Clause E3 – Internal Moisture). When waterproofing fails, water can silently track into wall cavities and subfloors for months before you notice visible damage. BRANZ research consistently identifies shower leaks as a leading cause of hidden moisture damage in NZ homes. The cost of repairing rotted framing or mould remediation far exceeds the cost of fixing the shower early.
Common Causes of a Leaking Shower
1. Failed or Cracked Grout and Silicone
This is the most frequent culprit. Grout is porous and, over time, it cracks, shrinks, or wears away — especially at movement joints like corners and the junction between the wall and floor. Once grout fails, water seeps behind tiles and into the substrate. Silicone sealant at corners and around fittings also degrades, hardens, and pulls away from surfaces over time.
2. Inadequate or Failed Waterproof Membrane
Under your tiles sits a waterproof membrane. In older NZ homes this may be a basic painted-on product, or it may have been applied incorrectly or skipped altogether. Membranes can crack, delaminate, or fail at joins and penetrations (where pipes pass through). Once the membrane is compromised, no amount of re-grouting will solve the problem long-term.
3. Leaking Shower Fittings and Plumbing
Worn tap washers, faulty cartridges, loose showerhead connections, or deteriorated seals around the drain can all allow water to escape. Sometimes the leak isn't through the tiles at all — it's from the plumbing itself.
4. Poor Original Installation
Many shower leaks in NZ homes — particularly those built or renovated before modern standards were tightened — stem from inadequate waterproofing at the time of construction. Tiles laid directly onto untreated plasterboard, missing upstands behind the shower tray, or insufficient membrane coverage are all common findings.
5. Movement and Settlement
Timber-framed NZ homes move with seasonal changes in temperature and humidity. This movement stresses grout lines and silicone joints, eventually causing them to crack and open up.
How to Diagnose Where the Leak Is Coming From
Before reaching for the silicone gun, it pays to identify the source:
- Dry test: Turn off the water and check if the leak stops. If it does, the issue is plumbing-related. If the shower base still shows moisture after a day or two of no use, the waterproofing membrane may be holding water.
- Visual inspection: Look for cracked, missing, or discoloured grout; silicone that has pulled away from corners; soft or hollow-sounding tiles (tap them — a dull thud suggests debonding); and staining or damp patches on adjacent walls or ceilings.
- Flood test: Block the drain and fill the shower base with water for 30 minutes, then check below for drips. This helps isolate whether the base or the walls are leaking.
What You Can Fix Yourself
| Issue | DIY Possible? | Notes |
|---|---|---|
| Regrouting surface grout | Yes | Use a grout rake to remove old grout, apply fresh grout, seal when cured |
| Replacing silicone at corners | Yes | Remove all old silicone, clean thoroughly, apply new sanitary-grade silicone |
| Replacing a showerhead | Yes | Straightforward — wrap threads with PTFE tape |
| Replacing tap washers | Caution | Simple washers are DIY; cartridge replacement may need a plumber |
| Repairing or replacing waterproof membrane | No | Requires tile removal and professional application |
For silicone and grout products, Mitre 10 and Bunnings stock a good range of sanitary silicones and tile grouts suitable for wet areas. Products from Ardex and Mapei are well regarded by NZ trades for waterproofing membranes and tile adhesives.
Important: Re-grouting and re-sealing is only a lasting fix if the membrane beneath is still sound. If the membrane has failed, surface repairs are a temporary measure at best.
The Proper Fix: Waterproofing Membrane Repair or Replacement
If the membrane has failed, the correct repair involves:
- Removing tiles in the affected area (sometimes the entire shower)
- Inspecting and repairing the substrate — replacing any damaged GIB Aqualine or fibre-cement sheet
- Applying a new waterproof membrane to the correct coverage and upstand heights per NZS 4858 (Wet Area Membranes)
- Allowing full cure time before retiling
- Retiling and grouting with appropriate wet-area products
This is skilled work. A professional waterproofer will ensure the membrane meets the Building Code and is applied correctly at all critical junctions — corners, penetrations, and the floor-to-wall upstand.
When to Call a Professional
Call a licensed waterproofer or tiler if:
- You suspect the membrane has failed
- Tiles are hollow, cracked, or debonding
- There is visible mould, soft walls, or damaged substrate
- The leak has been present for some time and damage may be hidden
Call a registered plumber (licensed through the Plumbers, Gasfitters and Drainlayers Board) if:
- The leak appears to be from pipework, the drain, or internal fittings
- You need to alter or replace any fixed plumbing — this is restricted work under NZ law and must be carried out by a licensed tradesperson
Safety note: Never ignore a persistent leak. Prolonged moisture can cause mould (a health hazard under the Healthy Homes Standards) and structural timber decay that becomes very costly to remediate.
You can find qualified local waterproofers, tilers, and plumbers on tradedirectory.co.nz.