Cracking tiles are one of the most common complaints from NZ homeowners, and the frustrating truth is that replacing a tile without fixing the root cause usually means the new one will crack too. Understanding why tiles crack is the first step to a lasting repair — and in many cases, the fix is more straightforward than you might think.
The Most Common Reasons Tiles Crack
There's rarely just one culprit. Tile cracking is almost always the result of movement, stress, or a preparation problem that was baked in from the day the tiles were laid. Here are the main causes to look for:
1. No Movement (Control) Joints
This is the single most common cause of cracked tiles in NZ. Tiles are rigid, but buildings move — they expand and contract with temperature and humidity changes, and they settle over time. Without movement joints (also called control joints or expansion joints) at regular intervals and at all changes of plane (e.g. floor-to-wall junctions), that stress has nowhere to go except into the tiles themselves. BRANZ guidelines and NZS 6952 recommend movement joints at specified spacings depending on the tile size and substrate type.
2. Substrate Movement or Deflection
Tiles need a solid, stable base. If your substrate (the surface beneath the tiles) flexes, the tiles will crack. Common culprits include:
- Timber floors with joists that are too widely spaced or undersized
- Particle board or thin plywood subfloors that flex underfoot
- Poorly cured or weak concrete slabs
- Wet area substrates that have softened due to water ingress
For tiled timber floors, the subfloor must be stiff enough to meet the deflection limits set out in NZS 3604 (the standard for light timber framing). A good rule of thumb: if the floor bounces or feels springy when you walk on it, it's not suitable for tiling without reinforcement.
3. Incorrect or Insufficient Adhesive Coverage
If tiles are not fully bedded in adhesive, they can crack when point-loaded (e.g. someone standing on a tile that has a void beneath it). The standard requires full coverage — typically at least 95% in wet areas and 80% in dry areas — using the correct notched trowel size for the tile format. Large-format tiles (600mm and above) are especially prone to cracking if coverage is poor.
4. Wrong Adhesive for the Application
Using a basic wall tile adhesive on a floor, or a standard adhesive in a wet area, can lead to bond failure and cracking. Always use a product rated for the specific application. Reputable NZ suppliers like Ardex and Mapei offer adhesive systems designed for floors, wet areas, underfloor heating, and exterior use — each with different flexibility ratings.
5. Underfloor Heating Without Flexible Adhesive
Underfloor heating systems cause tiles to expand and contract with every heating cycle. If a standard (non-flexible) adhesive and grout were used, cracking and debonding are almost inevitable over time. Flexible adhesives and grouts, along with correctly placed movement joints, are essential for heated tile installations.
6. Impact Damage
Sometimes a crack really is just a crack — caused by dropping something heavy. Hairline cracks from impact are usually isolated to one tile and don't spread. If you're seeing multiple tiles cracking in a pattern, however, impact is rarely the cause.
7. Poor Quality or Unsuitable Tiles
Using wall tiles on a floor, or selecting tiles with a low PEI rating (abrasion resistance) for a high-traffic area, can result in surface crazing and cracking over time. Always check the tile's rating matches its intended use.
How to Diagnose the Problem
Before you replace anything, do a simple tap test: use a coin or the handle of a screwdriver to tap across your tiles. A hollow sound indicates the tile has debonded from the substrate — a key sign that adhesive coverage was poor or the substrate has moved. Solid-sounding tiles that are cracked point more toward substrate deflection or missing movement joints.
| Symptom | Likely Cause |
|---|---|
| Multiple tiles cracking in a line | Missing movement joint |
| Hollow sound when tapped | Poor adhesive coverage / debonding |
| Cracks at wall-floor junction | No cove/movement joint at change of plane |
| Single isolated crack | Impact damage |
| Cracking near heat source | Thermal movement, wrong adhesive |
| Widespread crazing | Wrong tile type for application |
Can You Fix It Yourself?
Replacing an isolated cracked tile is a manageable DIY job for a handy homeowner — you'll need a grout saw, cold chisel, hammer, appropriate adhesive, and matching grout. The key is to fix the underlying cause first, or the new tile will crack again.
However, if the cracking is widespread, or if the tiles are in a wet area (shower, bathroom floor, or around a bath), be cautious. Wet area tile work must comply with NZS 8500 and the NZ Building Code clause E3 (Internal Moisture). Disturbing wet area tiles without understanding the waterproofing membrane beneath can lead to water damage inside your walls and floors — a much more expensive problem. You can find products and advice at Bunnings or Mitre 10, but if in doubt, get a professional assessment first.
When to Call a Professional
Call a qualified tiler if:
- Multiple tiles are cracking or hollow-sounding across a large area
- The cracking is in a wet area (shower, bathroom, laundry)
- You suspect substrate or structural movement is the cause
- The original installation was recent and may be a workmanship issue (you may have a claim)
- You're planning a full retile and want it done right the first time
A licensed tiler will assess the substrate, specify the correct system, and install movement joints in the right locations. You can find qualified local tilers on tradedirectory.co.nz.
Safety note: If cracked tiles are in a wet area and you suspect water has been getting behind the wall lining, have a professional check for mould and structural damage before proceeding with any repairs.