Walk into any building defects tribunal in NSW and you will find tiling disputes near the top of the list. The complaint is almost always the same: tiles that are uneven, grout lines that crack within months, shower floors that pond water, or floor tiles with visible lips that inspectors flag immediately.
Trace the cause back and you almost always land in the same place. The substrate was not properly levelled before a single tile was laid.
Getting the level right is not a finesse skill saved for later in your trade career. It is the foundation skill — the one that determines whether everything that follows lasts 25 years or has to be ripped out in five. This article explains exactly what level means in a tiling context, what the Australian Standards require, and where tilers most commonly go wrong.
Core principle: A tiler's job is to apply a flat, level, or correctly-drained surface on whatever the builder hands them. If the substrate is wrong, no amount of skill with the tiles themselves will produce a compliant, durable result. Substrate assessment and preparation is the first — and most important — step in any tiling job.
In everyday speech, "level" means horizontal. In tiling, the word covers three distinct but related concepts — and confusing them is one of the most common errors apprentice tilers make.
A flat surface has no humps, hollows, or undulations. It doesn't have to be horizontal — a wall is flat but not level. Flatness is measured by laying a straightedge across the surface and checking the gap beneath it. Under AS 3958.1, the maximum permissible deviation is 3mm under a 1800mm straightedge for most floor applications.
A level surface is both flat and truly horizontal. Floor tiles in dry areas — living rooms, hallways, bedrooms — must be installed level. A noticeably non-level floor is a defect regardless of how well the tiles are laid.
Wet areas must not be level — they must slope deliberately toward a drain. This intentional gradient is called the fall. Under AS 3740:2021, shower floors require a minimum fall of 1:60 to the drain — approximately 17mm per linear metre. A shower floor that is perfectly level will pond water, promote mould, and cause waterproofing failure beneath the tiles.
Australian Standards reference:
AS 3958.1:2007 — Guide to the Installation of Ceramic Tiles. The primary standard for substrate flatness tolerances and installation methods.
AS 3740:2021 — Waterproofing of Domestic Wet Areas. Governs minimum fall requirements in all wet area tiling.
Tiling is a precision trade. Knowing the tolerances is required knowledge for your CPC31320 qualification and for producing work that will pass inspection.
| Application | Maximum Deviation | Standard |
|---|---|---|
| General floor areas (ceramic/porcelain) | 3mm under 1800mm straightedge | AS 3958.1 |
| Large format tiles (600mm+ side) | 3mm under 3000mm straightedge | AS 3958.1 + tile mfr specs |
| Shower floor fall to drain | Minimum 1:60 (17mm per metre) | AS 3740:2021 |
| Balcony / external wet area fall | Minimum 1:80 (12.5mm per metre) | AS 3740:2021 |
| Lippage — residential (grout joint ≥ 3mm) | Max 1mm between adjacent tiles | AS 3958.1 / ATFA guidelines |
| Lippage — commercial (rectified tiles) | Max 0.5mm | ATFA / project specification |
| Wall tiles (ceramic, internal) | 4mm under 1800mm straightedge | AS 3958.1 |
⚠ Large format tile warning: Large format tiles (600×600mm and above) amplify substrate imperfections dramatically. A 2mm hollow invisible under 300×300mm tiles will create visible lippage under a 600×600mm tile. The substrate must be flat to within tolerance over the full 3000mm span — not just locally. If you're working with large format tiles, assess the substrate with a longer straightedge before you pick up a trowel.
Substrate assessment is where the work actually begins. A qualified tiler does not pick up a trowel until they have completed a full level survey of the installation area.
On any job larger than a single bathroom, set up a rotating laser level on a tripod in the centre of the space. Establish a consistent height reference across the full floor area and mark it on the walls. Every measurement you take comes back to this datum. Without it, errors compound across the floor.
Walk the floor with a 1800mm spirit level or digital level, checking in multiple directions — not just parallel to the walls. Diagonal checks catch humps and hollows that run diagonally across the slab, which are common in poured concrete. Mark every high point with chalk (↑) and every low point (↓).
✅ Pro tip — never correct level with adhesive: Varying the adhesive bed thickness to compensate for an unlevel substrate is one of the most common defects identified in tiling disputes. Adhesive is not a levelling compound. Using more in low spots leads to inconsistent coverage, hollow tile, and adhesive failure. The substrate must be within tolerance before adhesive is applied — full stop.
Floor levelling compounds typically require 24–48 hours before light foot traffic and 72 hours or more before tiling, depending on the product and conditions. In cold or humid environments, allow more time. Tiling over a levelling compound that hasn't fully cured is a leading cause of adhesive failure on renovated floors.
Fall is the aspect of levelling that trips up the most tilers, including experienced ones. It seems straightforward — slope the floor toward the drain — but executing it correctly across an entire shower floor, especially with large format tiles, is a genuine skill.
The finished tile surface at the drain must be the lowest point on the floor. If the drain is 200mm from the rear wall, you need a minimum fall of 200 ÷ 60 = 3.3mm from rear wall to drain edge — plus the drain outlet height. Every part of the floor surface must drain continuously to that point.
After laying but before grouting, pour a litre of water onto the shower floor and watch what happens. All water should reach the drain within 15–20 seconds. Any ponding is a defect that must be corrected before grout goes in. Ponding areas almost always indicate a reversal of fall caused by lippage in one corner.
AS 3740:2021 requirement: "The finished surface of floor tiles in wet areas shall be graded to drain freely to a floor waste or gutter with a minimum fall of 1:60." This applies to the finished tile surface — not the substrate before tiling. Account for tile and adhesive bed thickness when preparing the substrate.
The biggest challenge in modern bathroom tiling is using 600×600mm or larger tiles in a shower that requires a 1:60 fall. A large flat tile cannot simultaneously be flat and follow a multi-directional curved fall across its full face. The solution: use a linear (channel) drain running across the full shower width, so the fall is in one direction only. A simple single-plane gradient that large format tiles can follow without creating lippage.
You cannot do level work well with inadequate tools. A qualified tiler's kit for substrate assessment includes:
In the CPC31320 Certificate III in Wall and Floor Tiling, substrate assessment and preparation — including levelling and fall — is one of the first competencies you develop. It's foundational because without it, nothing else you learn produces durable, compliant work.
The ATFA (Australian Tile & Façade Association) estimates that substrate-related defects account for the majority of all tiling failures in residential construction. Nearly never bad tiles or bad adhesive — almost always good materials laid on a bad surface.
A builder can hand a tiler an out-of-tolerance slab and expect it to work. A qualified tiler knows exactly what the tolerances are, can identify when a substrate fails to meet them, communicates that clearly to the builder or client, and knows how to remediate it before a single tile goes down. That knowledge — and the confidence to use it — is what separates a tradesperson from a labourer with a trowel.
The professional standard: If you lay tiles over a substrate that is outside tolerance, the resulting defects are your liability — regardless of who prepared the substrate. A qualified tiler does not lay on an unlevel surface without either remediating it, or documenting the condition in writing and obtaining a client sign-off accepting the risk. This is standard professional practice, and it is covered in your CPC31320 training.
Learn substrate preparation, levelling, wet areas, large format tiles, and every other competency in the CPC31320 at our purpose-built workshop in Lidcombe, Sydney. Domestic and international students welcome.
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