Laying large format tiles on a bathroom floor is technically within reach for a capable DIYer — but it's one of the more demanding tiling jobs you can tackle. The bigger the tile, the less room for error: an uneven substrate, a slight lippage between tiles, or the wrong adhesive can all cause costly problems. Here's what you need to know before you start.
What Are Large Format Tiles?
Large format tiles are generally considered to be any tile with at least one edge over 600 mm, though many popular bathroom floor tiles now come in 600×600 mm, 800×800 mm, or even 1200×600 mm sizes. Their appeal is real — fewer grout lines, a cleaner look, and a sense of space — but their size creates specific challenges around substrate flatness, adhesive coverage, and handling.
NZ Building Code Considerations
Bathroom floors fall under NZ Building Code clause E3 (Internal Moisture) and G12 (Water Supplies). While tiling itself is generally not restricted work, the waterproofing membrane beneath the tiles absolutely matters. Under the Building Code, wet areas like shower floors and around baths must be properly waterproofed. If your bathroom renovation involves moving walls, altering drainage, or changing the layout significantly, you may need a building consent — always check with your local council before starting. Minor like-for-like tile replacements often fall under Schedule 1 exemptions, but confirm this with your council rather than assuming. You can find guidance at MBIE Building Performance.
Substrate: The Most Critical Step
Large format tiles are unforgiving of an uneven floor. The industry standard for flatness is no more than 3 mm variation over a 3-metre straightedge (refer to BRANZ guidelines and tile manufacturer specs). In NZ bathrooms, you'll typically be tiling over:
- Concrete slab — usually a good base, but check for cracks and level any dips with a floor levelling compound
- Fibre-cement sheet (such as James Hardie's Villaboard) — a common and recommended substrate in NZ wet areas
- Plywood — can work but must be exterior-grade, well-fixed, and properly primed; check your tile adhesive manufacturer's recommendations
- Existing tiles — tiling over old tiles is sometimes possible but adds height and requires a sound, flat surface
Avoid tiling directly over standard GIB plasterboard on floors — it is not suitable for wet area floor use.
Waterproofing: Don't Skip This
Before any tiles go down in a wet area, a waterproofing membrane must be applied. This is non-negotiable under the NZ Building Code. Products like Ardex or Mapei offer membrane systems designed for this purpose. Follow the manufacturer's instructions carefully — curing times matter. If you're unsure about the waterproofing stage, this is a good point to bring in a professional.
Tools and Materials You'll Need
Large format tiles require some gear that goes beyond a basic tiling kit:
| Item | Why It Matters |
|---|---|
| Large-notch trowel (10–12 mm square notch) | Ensures full adhesive coverage under big tiles |
| Back-buttering technique | Eliminates voids — essential for tiles over 600 mm |
| Tile levelling/lippage system | Keeps edges flush between tiles |
| Wet saw or angle grinder with diamond blade | Clean cuts on large, often porcelain tiles |
| Long spirit level or laser level | Checks flatness across the whole floor |
| Suction cup lifters | Large tiles are heavy — protect your back |
Adhesive choice is critical. Use a flexible, large-format tile adhesive rated for your substrate. Brands like Ardex, Mapei, and Sika all offer suitable products available from Bunnings, Mitre 10, or PlaceMakers. Always read the datasheet and match the adhesive to your specific substrate and tile type.
Key Techniques for Large Format Tiles
- Back-butter every tile in addition to trowelling the floor — aim for full adhesive coverage in wet areas — check your tile adhesive manufacturer's datasheet and relevant standards for the specific minimum coverage requirement
- Use a tile levelling system (plastic clips and wedges) to eliminate lippage between tiles — a trip hazard and an eyesore
- Plan your layout carefully — find the centre of the room, dry-lay tiles first, and avoid thin slivers at edges
- Allow for movement joints at walls and in large floor areas as per manufacturer guidelines — large format tiles and rigid adhesives need room to breathe
- Check the fall toward the floor waste — NZ bathrooms require adequate drainage fall, typically around 1:60 to 1:80 toward the drain
Safety Notes
Large porcelain tiles are heavy and have sharp edges when cut. Wear safety glasses, gloves, and hearing protection when cutting. A wet saw reduces dust significantly — dry cutting creates silica dust, which is a serious health hazard. See WorkSafe NZ for guidance on working safely with silica-containing materials.
When to Call a Professional
Consider hiring a qualified tiler if:
- Your substrate is uneven, damaged, or you're unsure what's underneath
- The bathroom involves any plumbing changes — moving a floor waste or altering pipework is restricted work under the Plumbers Gasfitters & Drainlayers Board and must be done by a licensed tradesperson
- Any electrical work (such as underfloor heating) is involved — this is restricted electrical work requiring a registered electrician licensed with the EWRB
- You want a guaranteed, professional finish on an expensive tile
A skilled local tiler will have the tools, experience, and product knowledge to get the job done right the first time. You can find qualified tilers in your area at tradedirectory.co.nz.
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