Getting wall tiles to stay perfectly level while the adhesive sets is one of the trickiest parts of any tiling job. Tiles are heavy, walls aren't always flat, and standard adhesives take time to cure — meaning tiles can slip or shift before they're locked in place. The good news is that with the right tools and a bit of preparation, you can achieve a professional result even as a first-timer.
Why Tiles Slip on Walls
Wall tiles fight gravity from the moment you press them into place. The main culprits for slipping or misalignment are:
- Adhesive that's too wet or applied too thickly — this reduces initial grab
- Heavy or large-format tiles — anything over 300×300 mm is more prone to sliding
- Uneven or unprepared substrate — lumps and hollows make consistent bedding impossible
- Skipping tile spacers — without spacers, tiles drift and joints become uneven
Understanding these causes helps you prevent problems before they start.
Prepare Your Surface First
A flat, solid substrate is the foundation of a level tile job. On wet areas like showers and bathrooms, the NZ Building Code clause E3 requires waterproofing membranes to be correctly applied before tiling. GIB and fibre-cement sheet (such as products from James Hardie) are common backer boards used behind wall tiles in NZ bathrooms.
Before you start, check your wall with a long spirit level or straight edge. Any high spots should be sanded back; low spots can be built up with a suitable base coat. A flat wall means your adhesive bed can be consistent, which is the single biggest factor in keeping tiles level.
Choose the Right Adhesive
For wall tiles, use a non-sag or wall-tile adhesive — these are formulated with higher initial grab so tiles don't slide. Standard floor adhesives are often too fluid for vertical surfaces. Products from Ardex and Mapei both offer wall-specific tile adhesives widely available in NZ. Sika also supplies adhesive systems suited to wet-area wall tiling.
Mix adhesive to the manufacturer's consistency — it should hold a peak when you pull the notched trowel away. If it slumps, it's too wet.
Use the Right Notched Trowel
Apply adhesive with a notched trowel matched to your tile size. As a general guide:
| Tile Size | Trowel Notch Size |
|---|---|
| Up to 200×200 mm | 6 mm V-notch |
| 200–400 mm | 8–10 mm square notch |
| 400 mm and over | 10–12 mm square notch |
For larger tiles, also back-butter the tile itself (apply a thin skim of adhesive to the back of the tile) to ensure full coverage and better bond. BRANZ recommends a minimum 80% adhesive coverage for wall tiles in dry areas, and higher coverage in wet areas.
Use Tile Spacers Consistently
Tile spacers are small plastic crosses or T-shapes that sit between tiles to maintain even grout joints. Common sizes in NZ are 2 mm, 3 mm, and 5 mm. Push them in at each corner junction as you go. Remove them before the adhesive fully cures (usually after a few hours) so they don't interfere with grouting.
For a cleaner result, use wedge spacers rather than cross spacers — these allow you to fine-tune the gap and are easier to remove.
Use a Tile Levelling System
For larger tiles or if you want a truly professional finish, a tile levelling system (TLS) is a game-changer. These systems use plastic clips inserted under the tile edges and a tightening wedge or cap that pulls adjacent tiles into the same plane, eliminating lippage (where one tile edge sits higher than the next).
How to use a levelling system:
- Press the first tile into the adhesive and check it's plumb and level with your spirit level.
- Insert the clip base under the edge of the tile before placing the next tile.
- Place the adjacent tile, then push the wedge or cap through the clip and tighten until both tile faces are flush.
- Once the adhesive has set, snap off the clip tabs with a rubber mallet — they're designed to break cleanly at the tile surface.
Levelling systems are available at Bunnings and Mitre 10, and are well worth the small extra cost on any job with tiles larger than 300 mm.
Work From a Datum Line
Always establish a datum (reference) line before you start. Use a long spirit level or laser level to mark a perfectly horizontal line across the wall, typically one tile height up from the floor (accounting for any floor tile or skirting). Start tiling from this line upward, then return to tile below it once the upper tiles have set.
This prevents the common mistake of following a floor that isn't level, which causes your tile rows to drift visibly out of horizontal.
Let the Adhesive Cure Properly
Don't rush the process. Most wall tile adhesives reach initial set within a few hours but should be left to cure fully — often 24 hours or more — before grouting. Check the manufacturer's datasheet for specific times, as this varies by product and NZ climate conditions (cold, damp South Island winters will slow curing significantly).
Avoid knocking or loading the tiles during this period.
When to Call a Professional
If your bathroom or shower tiling involves waterproofing membranes, this work must comply with NZ Building Code clause E3 and is best carried out by — or at least checked by — a qualified tiler or builder. Poorly applied waterproofing is one of the leading causes of costly water damage in NZ homes.
For large-format tiles (600 mm and above), complex patterns, or heritage homes with uneven walls, hiring an experienced tiler will save you time and frustration. You can find qualified local tilers on tradedirectory.co.nz.