A floor needs to be flat, sound and dry before any tile goes down, and levelling is how you get there when the substrate is out. For most Adelaide homes that means a self-levelling compound for shallow dips or a sand and cement screed for deeper builds and falls, checked against a straightedge before a single tile is laid.
This guide walks through how levelling actually works, when to reach for compound versus screed, how to check for falls and dips, and why getting it right matters most for large-format tiles. It sits within our Floor Tiling in Adelaide: The Homeowner's Guide.
Why level matters before you tile
Tiles are rigid. They do not bend to follow a floor that dips and rolls, so any unevenness in the substrate ends up showing in the finished surface or, worse, cracking the tiles later.
Get the base wrong and you invite the classic problems:
- Lippage: one tile edge sitting proud of the next, which you feel underfoot and catch with a mop.
- Hollow or drummy tiles: voids under the tile where the adhesive did not make full contact, which crack under load.
- Cracked tiles and grout: an unsupported tile over a dip flexes and eventually fails.
- Water pooling: in wet areas and outdoors, a floor that falls the wrong way sends water where you do not want it.
Fixing any of this after the fact means lifting finished tiles, and that is a job in itself. Our guide on tile removal cost in Adelaide shows why it pays to get the base right the first time.
How flat does the floor actually need to be?
The industry benchmark is a maximum deviation of roughly 3mm under a 2 metre straightedge, and tighter still for large tiles. In practice a good tiler lays a long aluminium straightedge across the floor in several directions and looks for gaps of light underneath.
There is an important distinction here:
- Level means truly horizontal, checked with a spirit level. Most interior floors want to be level.
- Flat means no dips or humps, checked with a straightedge, regardless of whether the floor is dead level.
- Fall means a deliberate, controlled slope, used in showers, laundries, balconies and around drains so water runs to the outlet.
A floor can be flat but not level, or level but not flat. Tiling wants flat above all, plus the right fall where water is involved.
Checking for falls and dips
Before deciding on a product, the floor gets read properly. On an Adelaide slab or timber subfloor, that means:
- Sweep and inspect. Loose material, old glue, paint and high spots all get dealt with first. High spots are often ground back rather than built up around.
- Run a straightedge. A 2 metre level laid across the floor in a grid reveals the dips and humps. Gaps get marked straight onto the floor with a pencil or chalk.
- Check the fall in wet areas. In a shower or laundry, the fall to the drain is checked with a level. Australian Standards want a graded fall to the waste, and a floor that is dead flat here is a defect, not a feature.
- Find the datum. For a whole room the tiler picks the highest point of the floor as the reference, because you can build up to meet it but you cannot dig the slab down.
This read tells you how deep the correction needs to be, which is what decides between compound and screed.
Self-levelling compound vs screed
These are the two main tools, and they solve different problems. Choosing the wrong one is a common and expensive mistake.
Self-levelling compound is a fine, pourable mix that you spread and it settles to find its own level. It is fast, smooth and ideal for shallow, general flattening of an interior floor. It does not create falls on its own, because by definition it finds level.
Screed is a stiffer sand and cement mix, trowelled and worked by hand to a set height. It handles deeper builds, steep falls and shower bases, and it can be laid much thicker than compound. It takes real skill to get flat and it cures more slowly.
Here is how they compare:
| Factor | Self-levelling compound | Sand and cement screed | | --- | --- | --- | | Best for | Shallow dips, general flattening | Deep builds, falls, shower bases | | Typical depth | 2mm to 10mm (some to 30mm) | 10mm to 75mm or more | | Creates a fall? | No, it finds level | Yes, worked by hand | | Finish | Very smooth, ready to tile | Flat but coarser, tile straight over | | Skill required | Moderate | High | | Cure before tiling | Often next day | Several days, sometimes longer |
As a rough Adelaide guide, floor levelling is costed at around $25 to $50 per square metre, on top of the tiling itself. It should appear as its own line on a quote rather than being buried, so you can see it has been allowed for. You can see how that fits the bigger picture in our floor tiling cost per m2 in Adelaide breakdown.
Whichever product is used, the slab underneath usually needs priming first so the compound or screed bonds properly. Skipping the primer is a shortcut that shows up later as a debonded, drummy floor.
Why level matters most for large-format tiles
Large-format tiles (anything from 600mm x 600mm upward, and the big 800mm and 1200mm planks now common in Adelaide new builds and renovations) are the least forgiving tile you can lay.
The reason is simple geometry. A small 300mm tile can ride over a gentle dip because it only spans a short distance. A 1200mm tile bridges that same dip and either rocks, sits hollow in the middle or shows obvious lippage at the joints where two big tiles meet.
Because of this, large-format work demands:
- A flatter base. The 3mm tolerance often tightens to around 2mm for big tiles.
- More levelling. Floors that would pass for small tiles routinely need compound or screed before large-format goes down.
- Levelling clips as well. Tile levelling spacers help during laying, but they are a finishing aid, not a substitute for a flat floor.
If you are weighing up tile sizes, our comparison of large-format vs standard floor tiles covers where the extra prep is worth it and where a standard tile saves you money and hassle.
Getting it right on your floor
The honest summary: levelling is not glamorous, but it is the part of a floor tiling job that decides whether the finish lasts 20 years or fails in 2. The floor gets read with a straightedge, corrected with compound or screed to suit the depth, primed, cured, and only then tiled. Anyone quoting your job should be able to walk you through exactly this.
A licensed, experienced tiler prices levelling honestly because they know skipping it comes back on them. That is exactly the kind of tradesperson worth comparing. When you are ready, we can connect you with vetted Adelaide floor tilers who will assess your substrate and quote the prep properly.
Tell us about your floor and request free quotes from trusted local tilers, with no obligation.