Cracking or loose tiles are more than just an eyesore — left untreated, they can let moisture into your subfloor or walls, leading to costly structural damage. The good news is that with a bit of detective work, you can usually identify the root cause and decide whether it's a quick DIY fix or a job for a qualified tiler. Here's what you need to know.
Common Causes of Cracking and Loose Tiles
Tiles don't fail on their own — something underneath or around them has usually gone wrong. The most frequent culprits in New Zealand homes include:
- Inadequate adhesive coverage: If the tile adhesive (also called tile adhesive or tile cement) wasn't spread properly, hollow spots form beneath the tile. Over time, foot traffic or movement causes the tile to crack or pop off.
- Movement in the substrate: Timber subfloors flex naturally, especially in older NZ homes. If the subfloor is too springy or the wrong tile adhesive was used, tiles can't cope with the movement and crack.
- Missing or incorrect expansion joints: Tiles and the materials beneath them expand and contract with temperature changes. Without proper expansion joints, built-up stress has nowhere to go — tiles crack or tent (lift in the middle).
- Moisture damage: Water getting under tiles — common in bathrooms and kitchens — can break down adhesive bonds and cause tiles to lift. This is a particular concern in NZ wet areas governed by MBIE Building Performance under Building Code clause E3.
- Poor-quality or wrong adhesive: Using a wall adhesive on a floor, or a standard adhesive on a heated floor (underfloor heating), will cause premature failure.
- Settlement or structural movement: New builds or homes on reactive soils (common in parts of Auckland and Hawke's Bay) can experience foundation movement that cracks tiles.
- Impact damage: A heavy object dropped on a tile can crack it, even if the installation was perfect.
Symptoms to Watch For
| Symptom | Likely Cause |
|---|---|
| Hollow sound when tapped | Poor adhesive coverage / hollow spots |
| Tile lifts at edges or corners | Moisture ingress or missing expansion joints |
| Cracked tile with no impact | Substrate movement or stress |
| Multiple tiles cracking in a line | Structural movement or crack in substrate |
| Grout crumbling or discolouring | Moisture, movement, or wrong grout used |
| Tiles tenting (arching upward) | Thermal expansion with no expansion joints |
How to Diagnose the Problem Step by Step
Step 1: The Tap Test
Kneel down and tap each tile firmly with your knuckle or a small rubber mallet. A solid thud means good adhesion; a hollow click means there's a void beneath. Mark hollow tiles with a piece of masking tape.
Step 2: Check the Grout Lines
Look closely at grout lines for cracks, gaps, or crumbling. Grout that's cracked in a consistent pattern — especially diagonal lines — often points to substrate movement rather than a one-off installation fault.
Step 3: Look for Moisture
In bathrooms and laundries, press gently on suspect tiles. Any flex or sponginess suggests the substrate (often fibre-cement sheet or compressed sheet) has been compromised by water. Check BRANZ guidance on wet area construction for what's required.
Step 4: Inspect the Subfloor (if accessible)
If you have access under the floor (e.g., a suspended timber floor), check for sagging joists, rot, or excessive bounce. Deflection in a timber subfloor is one of the most common reasons floor tiles crack in NZ homes.
Step 5: Check for Expansion Joints
Look at the perimeter of the tiled area and at any internal corners. There should be a flexible sealant joint (not grout) at walls and columns. Missing expansion joints are a very common installation fault.
What You Can Safely Fix Yourself
Replacing an isolated cracked tile is a manageable DIY job if the substrate is sound:
- Score around the grout lines with an oscillating multi-tool or grout saw.
- Carefully chisel out the broken tile, working from the centre outward to avoid damaging neighbouring tiles.
- Scrape off old adhesive from the substrate until you have a clean, flat surface.
- Apply fresh tile adhesive — products from Ardex or Mapei are widely available at Mitre 10 and Bunnings — using a notched trowel.
- Press the new tile firmly into place, checking it's level with surrounding tiles. Use tile spacers to maintain consistent grout lines.
- Allow to cure as per the adhesive manufacturer's instructions, then regrout.
Re-grouting crumbling or cracked grout (where tiles are still firmly bonded) is also a DIY-friendly task using a grout rake and fresh grout.
Important: If you find moisture damage, mould, or a spongy substrate beneath the tiles, stop — this needs professional assessment before retiling.
How to Prevent Tiles Cracking or Coming Loose Again
- Always use the correct adhesive for the application — floor-rated, flexible adhesive for floors; waterproof adhesive in wet areas.
- Ensure full adhesive coverage (at least 95% in wet areas, 80% in dry areas as a general guide per good trade practice).
- Install expansion joints at perimeters and at intervals across large tiled areas.
- Fix any subfloor flex before tiling — a rigid, stable substrate is non-negotiable.
- In wet areas, use a proper waterproof membrane behind tiles. This is required under the NZ Building Code.
- Choose the right grout — unsanded grout for narrow joints, sanded or epoxy grout for wider joints and high-traffic areas.
When to Call a Professional
Call a qualified tiler if:
- Multiple tiles are cracking or lifting — this usually signals a systemic problem with the substrate or installation.
- You find moisture damage, rot, or mould beneath tiles, especially in bathrooms or kitchens. Wet area waterproofing must comply with Building Code clause E3, and getting it wrong can void your home insurance.
- Tiles are tenting or lifting across a large area — this often requires full removal and reinstallation.
- The problem is in a wet area (shower, bath surround) where waterproofing is involved. Poorly waterproofed wet areas are one of the leading causes of serious water damage in NZ homes.
- You suspect structural movement is the cause — a builder or engineer should assess this before any retiling.
A licensed tiler will also know when a job requires a Licensed Building Practitioner (LBP) — for example, if structural work to the subfloor is needed. You can find qualified, vetted local tilers on tradedirectory.co.nz.
Safety note: There is no restricted electrical, gas, or plumbing work involved in standard tiling. However, if your tiled floor has underfloor heating, any work on the heating element itself must be carried out by a registered electrician — see the Electrical Workers Registration Board for what's restricted.
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