Large-format tiles need a particularly flat, stable substrate because their size makes even small wall irregularities much harder to accommodate. As a general benchmark, walls being tiled with adhesive should have no gaps greater than 3mm beneath a 2m straightedge. With very large tiles or panels, an even flatter surface may be required to achieve good adhesive coverage and minimise lippage.
Large-format porcelain has transformed bathroom and interior design.
Fewer grout joints, realistic stone and marble effects and expansive surfaces can create a premium, almost seamless appearance.
But large tiles are also far less forgiving of poor preparation.
A dip or high spot that might be relatively easy to disguise behind a small ceramic wall tile can become a major problem when installing a tile measuring 600 x 1200mm or larger.
This can lead to:
- visible lippage;
- uneven grout lines;
- poor adhesive contact;
- difficulty aligning adjoining tiles;
- hollow areas;
- tile stress;
- problems around trims, corners and niches.
For large-format tiling, preparing the wall correctly is often more important than trying to adjust the tiles during fixing.
How flat does a wall need to be for large-format tiles?
The Tile Association advises that wall surfaces receiving tiles fixed with adhesive should be plumb and sufficiently flat so that gaps beneath a 2 metre straightedge do not exceed 3mm.
That is an important starting point.
However, large-format tiles and panels can require even greater accuracy.
The Tile Association notes that large-format products need very flat substrates because their size makes it difficult to compensate by varying adhesive thickness. In practice, smoothing materials, levelling systems or tile backer boards may be required to achieve the necessary plane.
Before tiling, place a long straightedge against the wall:
- vertically;
- horizontally;
- diagonally;
- across several different areas.
Check for both gaps and rocking.
The aim isn’t simply to make the wall look reasonably straight. It needs to provide a sufficiently consistent plane for the tile and adhesive system.
Why are large-format tiles less forgiving of uneven walls?
Imagine placing a small tile across a shallow dip in a wall.
Because the tile is relatively short, the difference between one side and the other may be small.
Now place a 1200mm-long tile across the same surface.
The tile spans a much greater area, so high and low points beneath it become more significant.
Large tiles are also relatively rigid.
Rather than following the contour of the wall, they tend to bridge over low areas or rock across high spots.
That can cause two major problems:
Poor adhesive coverage
If the wall has significant low spots, parts of the tile may not make appropriate contact with the adhesive.
Lippage
One edge of a tile can sit higher than the neighbouring tile, creating a visible and sometimes tactile step between the two surfaces.
Both problems become more difficult to correct once installation has started.
What is tile lippage?
Tile lippage is the difference in height between the edges of neighbouring tiles.
Even when two tiles are correctly spaced, one edge can sit slightly higher or lower than the other.
Several things can contribute to lippage:
- uneven substrates;
- bowed tiles;
- poor setting-out;
- inconsistent adhesive thickness;
- incorrect trowelling;
- inadequate tile adjustment;
- dimensional variation between tiles.
Large-format tiles can make lippage more noticeable because of their long edges and relatively small number of grout joints.
The best way to reduce lippage is to begin with a flat substrate.
A tile levelling system can then help maintain alignment between adjacent tiles, but it cannot compensate for a badly uneven wall.
Can a tile levelling system fix an uneven wall?
No.
This is one of the most common misunderstandings around tile levelling clips and wedges.
A levelling system helps control the relative position of neighbouring tiles while the adhesive cures.
It does not flatten the wall behind them.
Trying to pull large tiles into alignment across a badly uneven wall can:
- place excessive pressure on the tiles;
- create inconsistent adhesive beds;
- reduce coverage;
- make installation more difficult;
- potentially introduce stress into the tile.
The correct sequence is:
Prepare and flatten wall → apply adhesive correctly → position tiles → use levelling system to minimise lippage
Quantum’s Tylix/Forte tile levelling system can help with the final alignment stage once the substrate itself has been properly prepared.
Can you use extra adhesive behind large-format tiles to level the wall?
You should not use tile adhesive as a substitute for proper wall preparation.
Adhesives have specified bed-depth limits.
The Tile Association notes that substrates should already be sufficiently flat before tile fixing and that thin-bed adhesive installations should generally be within the 3mm-under-2m straightedge tolerance.
Using excessive adhesive to compensate for a poor wall can result in:
- excessive shrinkage;
- inconsistent curing;
- poor support;
- difficulty maintaining the tile plane;
- increased risk of movement or debonding.
If the wall needs substantial correction, fix the substrate, not the adhesive bed.
Is dot-and-dab acceptable for large-format wall tiles?
No.
Dot-and-dab fixing means placing isolated blobs of adhesive behind the tile rather than creating a continuous adhesive bed.
The Tile Association states that dot-and-dab is not an acceptable method for fixing tiles.
Large-format tiles need particularly careful adhesive coverage because of their size and weight.
The correct adhesive should be spread evenly using an appropriate notched trowel, with back-buttering used where required to achieve suitable contact.
Should you back-butter large-format tiles?
Back-buttering is commonly used with large-format tiles to improve adhesive contact.
It involves applying an additional thin layer of adhesive to the back of the tile before placing it into the combed adhesive on the wall.
Its purpose is to:
- improve coverage;
- reduce voids;
- improve contact with the adhesive bed.
It should not be confused with using thick patches of adhesive to correct an uneven background.
The wall should already be appropriately flat.
Back-buttering improves bonding, not wall levelling.
When should you use a tile backer board?
Where the existing wall is significantly uneven, damaged or unsuitable, creating a new tile-ready surface may be more reliable than trying to repair numerous isolated areas.
Tile backer boards are particularly useful in:
- renovation projects;
- bathrooms;
- showers;
- wet rooms;
- stud walls;
- older properties;
- walls containing mixed or inconsistent substrates.
Quantum supplies Baseboard and AquaBoard Eco for different applications.
Can Baseboard help create a flat wall for large-format tiles?
Baseboard is a waterproof tile backer board designed to provide a stable surface for tiling.
It can be particularly useful where an existing background needs to be overboarded or where a new flat tiling surface is being constructed.
Baseboard is suitable for applications including:
- bathrooms;
- wet rooms;
- showers;
- walls;
- suitable floors;
- renovation projects.
Because it is waterproof, Baseboard can also solve two issues at once in wet areas:
substrate preparation + waterproof tile-ready background
However, the underlying framing or wall still needs to allow the boards to be installed in a flat plane.
Attaching boards directly to a severely bowed structure without first correcting the fixing plane will simply reproduce the problem.
What about AquaBoard Eco?
AquaBoard Eco is a lightweight, moisture-resistant tile backer board designed to provide a stable surface for wall and floor tiling.
It can be useful where:
- an existing wall surface is unsuitable;
- a lightweight board is preferred;
- a stable surface is required before tiling.
It should be remembered that moisture-resistant is not the same as waterproof.
Where the wall forms part of a shower, wet room or frequently wet area, the complete waterproofing system must still be specified correctly.
Baseboard or AquaBoard Eco for large-format wall tiles?
| Requirement | Product to consider |
|---|---|
| Stable tile-ready board | Baseboard or AquaBoard Eco |
| Waterproof backer board | Baseboard |
| Lightweight moisture-resistant board | AquaBoard Eco |
| Shower/wet-room wall | Baseboard, or suitable board with separate waterproofing system |
| Uneven renovation background | Depends on wall construction and fixing method |
| Large-format tile installation | Whichever board/system creates the required flat, stable substrate |
The board itself is only one part of the specification.
The fixing method, framing, tile weight, adhesive and waterproofing requirements also need to be considered.
Why is substrate preparation especially important with marble-effect and stone-effect tiles?
Large marble-effect and stone-effect porcelain frequently features strong veining or continuous patterns.
Lippage can interrupt those patterns and make an otherwise premium installation appear uneven.
Light striking across a polished or satin surface can also make slight differences in tile height more noticeable.
This is one reason preparation is particularly important when installing large-format Navarro porcelain ranges.
Customers tend to focus on colour, veining and finish when selecting tiles.
Installers need to be equally focused on the wall behind them.
Should large-format tiles be installed on fresh plaster?
Only once the plaster is fully suitable for tiling.
The substrate must be:
- dry;
- fully cured;
- stable;
- sufficiently flat;
- capable of supporting the proposed tile weight.
If the newly plastered wall is not flat enough for the intended format, it should be corrected before the tile installation begins.
Large tiles should not be used as a means of hiding poor plastering.
Can you tile large-format porcelain onto plasterboard?
Potentially, but several factors need to be checked.
The board must be:
- securely fixed;
- suitable for the location;
- capable of carrying the combined tile and adhesive load;
- sufficiently flat;
- appropriately waterproofed where required.
Tile weight becomes increasingly important with large porcelain formats.
The background manufacturer’s loading limits and adhesive manufacturer’s recommendations should therefore be checked before specification.
How should large-format tiles be handled?
Preparation doesn’t stop at the wall.
Large-format tiles and panels also need to be handled carefully.
The Tile Association advises using suitable frames, suction cups and purpose-designed handling equipment for large-format porcelain because excessive flexing during transport or installation can create microfractures.
Cutting also requires suitable equipment and adequate tile support.
This becomes particularly important when creating:
- socket cut-outs;
- niches;
- pipe openings;
- corners;
- mitres;
- complex shapes.
How do you prepare an uneven wall for large-format tiles?
Step 1 – Check the wall
Use a 2m straightedge to assess:
- flatness;
- plumb;
- high spots;
- low areas.
Step 2 – Check the substrate condition
Identify:
- loose plaster;
- cracks;
- movement;
- moisture;
- paint or contamination;
- damaged areas.
Step 3 – Correct the substrate
Depending on the condition, this may involve:
- local repairs;
- suitable levelling/rendering;
- replastering;
- overboarding with a suitable tile backer board.
Step 4 – Waterproof where required
For showers and wet rooms, install an appropriate waterproofing system.
Quantum options include:
- Baseboard waterproof backer boards;
- AquaTank liquid tanking system;
- StructaMat Pro or WP where appropriate to the specification.
Step 5 – Plan the layout
Before mixing adhesive, determine:
- grout-joint positions;
- cuts;
- corners;
- niches;
- tile trims;
- sanitaryware positions;
- pattern alignment.
Step 6 – Use the correct adhesive and trowel
Choose adhesive according to:
- tile type;
- tile size;
- substrate;
- location;
- waterproofing or membrane system.
Step 7 – Back-butter where required
Ensure suitable adhesive contact across the tile.
Step 8 – Use levelling clips appropriately
Once the substrate is flat and the tiles are correctly bedded, a levelling system can help control lippage between neighbouring pieces.
Step 9 – Check continuously
Use a straightedge throughout the installation rather than waiting until the complete wall has been tiled.
What are the most common mistakes when installing large-format tiles on walls?
Trying to correct everything with adhesive
Fix the wall first.
Assuming a levelling system will flatten the installation
Levelling clips control neighbouring tiles, not the substrate.
Ignoring small high spots
One high point can affect a large area when a long tile bridges across it.
Poor adhesive coverage
Large tiles need consistent support.
Using dot-and-dab fixing
This creates unsupported areas behind the tiles.
Failing to check tile weight
The wall system must be capable of supporting the complete tiled finish.
Neglecting waterproofing
A flat shower wall still needs the appropriate waterproofing system.
Starting without a complete layout
Large tiles often mean large and expensive cuts. Setting out before fixing helps minimise awkward pieces and waste.
Large-format wall tiling checklist
| Before tiling | Check |
|---|---|
| Wall flatness | Maximum deviation appropriate for tile/system |
| Wall stability | No loose or unstable areas |
| Tile weight | Substrate suitable for total load |
| Wet-area requirement | Waterproof system specified |
| Tile layout | Cuts, joints and trims planned |
| Adhesive | Suitable for tile, substrate and format |
| Coverage | Correct fixing method and back-buttering where necessary |
| Levelling | Levelling system ready for lippage control |
| Cutting | Correct equipment available |
| Finished plane | Checked continuously during installation |
Frequently asked questions
Can you put large-format tiles on an uneven wall?
Only after the wall has been made sufficiently flat and stable. Large tiles are less tolerant of uneven backgrounds than smaller formats.
How flat should a wall be for tiles?
TTA guidance states that gaps beneath a 2m straightedge should generally not exceed 3mm for walls being tiled with adhesive. Large-format tiles may require an even flatter substrate for successful installation.
Do levelling clips stop lippage?
They can help reduce lippage between adjacent tiles during installation, but they cannot correct a badly uneven wall.
Can you use more adhesive behind one edge of a tile?
Only within the adhesive manufacturer’s permitted bed-depth range. Significant wall irregularities should be corrected before tiling.
Are large-format tiles suitable for bathrooms?
Yes. Large-format porcelain is widely used in bathrooms and can create a premium finish with fewer grout joints. Correct substrate preparation, waterproofing and installation remain essential.
Should you use tile backer board behind large-format tiles?
A backer board can be very useful where it provides the flat, stable and appropriate substrate required for the installation. The particular board and fixing system must also be capable of supporting the chosen tile.
Large-format tile preparation products from Quantum Group
Quantum Group supplies tile preparation, waterproofing, cutting and installation products through retailers, wholesalers, builders’ merchants and online retailers across the UK and Ireland.
For large-format wall installations, relevant Quantum ranges include:
Baseboard – waterproof tile backer boards for creating stable tile-ready substrates.
AquaBoard Eco – lightweight moisture-resistant backer boards.
AquaTank – liquid-applied waterproofing systems for wet areas.
StructaMat – movement and waterproofing solutions where the installation requires additional substrate management.
Tylix – levelling, cutting and installation tools for professional tiling.
Navarro Tiles – ceramic and porcelain collections including contemporary large-format designs.
For a broader guide to preparing irregular surfaces, read our How to Tile an Uneven Wall guide.