A leaking shower is one of the most common — and costly — problems NZ homeowners face. The good news is that many leaks are caused by failed silicone or grout joints rather than damaged tiles, meaning you can often fix the problem without ripping everything out. Here's how to diagnose the issue and reseal your shower properly.
Why Showers Leak
Before reaching for the caulking gun, it pays to understand what's actually failing. The most common culprits are:
- Failed silicone sealant in the corners and along the shower tray or base
- Cracked or missing grout between tiles, especially on walls and the floor
- Deteriorated waterproof membrane beneath the tiles (this is more serious)
- Leaking shower waste or drain seal
If water is appearing on the ceiling below, soaking into adjacent walls, or the leak has been going on for a long time, the waterproof membrane may be compromised — that's a job for a professional. But if the leak is minor and relatively recent, resealing the joints is a very reasonable first step.
Step 1 — Diagnose the Leak First
Do a simple plug test: block the shower drain with a rubber plug or bag of water, fill the base to about 20–30 mm, and leave it for 30 minutes. If the water level drops, the leak is in the base or drain area. If it holds, run the shower normally and check where water escapes — this points to wall joints or the screen seal.
Check all movement joints (the corners where walls meet the floor, and where the shower tray meets the wall) — these are the most common failure points because they flex slightly with the building's movement.
Step 2 — Gather Your Materials
For a DIY reseal you'll need:
- Silicone remover tool or sharp utility knife
- Grout rake or oscillating multi-tool (for removing old grout)
- Mould-resistant silicone sealant rated for wet areas (look for products from Sika or similar)
- Unsanded grout suitable for your tile joint width
- Grout float and sponge
- Methylated spirits or surface cleaner for degreasing
- Painter's tape for neat lines
You'll find most of these at Bunnings or Mitre 10. Always choose a silicone labelled mould-resistant and suitable for wet area/sanitary use.
Step 3 — Remove Old Silicone and Grout
This is the most important step — new sealant will not bond properly over old, contaminated material.
- Use a silicone remover tool or utility knife to carefully cut and peel away all old silicone from the corners and base joints.
- Rake out cracked or hollow grout to a depth of at least 5–6 mm using a grout rake.
- Clean the area thoroughly with methylated spirits or a dedicated surface prep cleaner. Remove all soap scum, mould, and dust.
- Allow the surface to dry completely — ideally 24–48 hours without using the shower. This is critical; silicone and grout will not cure or bond properly on a damp surface.
Step 4 — Regrout Where Needed
Mix your grout to a smooth, peanut-butter consistency and press it firmly into the raked joints using a grout float, working at a diagonal angle. Remove excess with a damp sponge before it sets. Allow to cure as per the manufacturer's instructions — typically at least 24 hours before getting it wet.
Do not grout the corner joints — these movement joints must be filled with flexible silicone, not rigid grout, which will crack again quickly.
Step 5 — Apply Fresh Silicone Sealant
- Apply painter's tape either side of the joint for a clean finish.
- Cut the silicone cartridge nozzle at a 45-degree angle to match your joint width.
- Apply a smooth, continuous bead of silicone into all corner joints and along the shower base.
- Wet your finger with a little soapy water and smooth the bead in one clean pass.
- Remove the tape immediately before the silicone skins over.
- Leave to cure fully — most wet-area silicones need at least 24 hours before water contact; check the product datasheet.
| Joint type | Use grout? | Use silicone? |
|---|---|---|
| Tile-to-tile (flat wall) | ✅ Yes | ❌ No |
| Corner (wall meets wall) | ❌ No | ✅ Yes |
| Wall meets shower base | ❌ No | ✅ Yes |
| Around drain/waste | ❌ No | ✅ Yes |
Step 6 — Check the Shower Screen Seal
Don't overlook the seal between the shower screen frame and the tiles. This is a common leak point. Remove old silicone and replace with a fresh bead, ensuring full contact with both the frame and the tile surface.
When to Call a Professional
Some situations are beyond a DIY reseal. Contact a qualified waterproofer or tiler if:
- The leak has been ongoing for months — the waterproof membrane under the tiles (required under NZ Building Code clause E3) may be damaged
- Tiles are hollow, loose, or lifting — the substrate may be wet and deteriorating
- You can see water staining or mould on the other side of the wall or ceiling below
- The shower base or tray is cracked
- You're unsure of the extent of the damage
A licensed waterproofer can assess whether the membrane is intact and, if needed, apply a trafficable waterproofing system over existing tiles in some situations — avoiding a full re-tile. BRANZ provides good guidance on wet area waterproofing standards for NZ conditions.
Note on plumbing: If the leak is coming from the waste fitting, drain, or supply pipes, this is restricted work under the Plumbers, Gasfitters and Drainlayers Act. It must be carried out by a licensed plumber registered with the PGDB. Do not attempt to modify drain connections yourself.
You can find qualified local waterproofers and tilers on tradedirectory.co.nz.