Large Format Tile and Slab Installation (120 x 260 cm)

The main reason is the look. On a wall about 2.6 metres high, one slab can run from floor to ceiling without a single horizontal joint. With a marble or concrete pattern, the wall then looks like one piece of stone.

• Fewer joints: fewer places for dirt and limescale to collect, so cleaning is easier.
• A calm surface: the room feels larger and more open because there is no grid of grout lines to catch the eye.
• Many uses: walls and floors, bathrooms, kitchens and living areas, as well as worktops, furniture panels or the cladding of a kitchen island.

For outdoor use, always check whether the manufacturer allows that particular slab outside and under what conditions. Not every large format slab is frost-resistant, and the build-up underneath an outdoor surface is more demanding.

This is not a job for a layperson. Depending on its thickness, one slab can weigh several tens of kilograms, and it breaks easily if it is lifted the wrong way. A tiler usually works roughly like this:

1. Checking and preparing the base. The wall or floor must be flat, firm, dry and clean. Flatness is checked with a long straightedge, not just a spirit level. Uneven areas are filled with a levelling plaster or a self-levelling compound. A primer suited to the type of surface is then applied.
2. Waterproofing. In showers and around baths, a liquid waterproofing membrane goes under the tiles, with sealing tape in the corners and collars around pipes.
3. Setting-out plan. Before the first cut, the tiler marks where the joints will fall and how they will meet doors, windows, niches and switches. With slabs this size, you cannot simply make up the difference at the end of the wall.
4. Handling and cutting. Slabs are carried on a mounting frame with vacuum suction cups. Straight cuts are made on a long rail cutter. Holes for taps and sockets are drilled with diamond core bits, preferably wet.
5. Bonding. The adhesive is a flexible cement-based type made for large formats. Under EN 12004 this is usually class C2 with a deformability rating of S1 or S2. Adhesive goes on both the base and the back of the slab. This is called back-buttering, and it stops hollow spots forming under the slab.
6. Levelling. Once placed, the slab is pressed and tapped firmly so the adhesive beds in fully. A levelling system with clips and wedges keeps neighbouring edges flush.
7. Grouting and flexible sealing. When the adhesive has cured, the joints are filled with grout. Corners, the join between floor and wall and the edges around a bath are not grouted but sealed with flexible silicone.
8. Cleaning. Adhesive and grout residue is removed while the work is in progress. Once it has set, it is hard to get off and the surface is easily damaged.

Two jobs of the same size in square metres can be very different in effort. These factors matter most:

• The condition of the base: a flat new wall is a very different job from an uneven old plaster wall in an older house or flat. The more levelling it needs, the longer the work takes.
• Getting the slabs into the home: a slab 260 cm long may not fit in a lift or go round a tight staircase. In a block of flats, agree the date and the route with the building management or owners' association.
• Number of holes and cut-outs: every socket, water outlet, corner window or niche needs a precise cut and carries a risk of breaking the slab.
• Room shape: a large flat wall goes quickly. A small bathroom with many corners and slopes is slow.
• Pattern matching: if the marble veining has to flow from one slab to the next, laying and cutting take longer.
• Underfloor heating: the screed must be dry and run through a heating-up cycle according to its protocol before tiling. Otherwise it may crack.

If sockets or switches have to be moved, a qualified, registered electrician does it, not the tiler. If the work includes demolition or changes to load-bearing walls, ask your local building authority beforehand what the local building regulations require in your case.

In practice, the same problems come up again and again. Years later they show as a cracked slab or a hollow sound when you tap it.

• Adhesive on the base only: with a surface this size, air pockets stay under the slab. On a floor, the slab then cracks under load.
• Underestimating flatness: a slight wave in a wall disappears under small tiles, but with a slab 260 cm long it creates a visible step at the edges.
• Missing movement joints: large areas and joins with other materials need a flexible movement joint. Without one, stress passes straight into the slabs.
• Joints too narrow: manufacturers usually set a minimum joint width, often around 2 mm. Butt joints look striking, but they leave the slabs no room to move.
• Lifting incorrectly: a slab carried flat without a frame bends and can crack before it is even laid.
• Grouting too soon: grouting should wait until the adhesive has cured as the manufacturer specifies, not start straight after laying.

Large format slabs come in different thicknesses. Thinner slabs are lighter and suit walls and furniture. Thicker ones are more often recommended for floors. When choosing, check:

• Approved use: whether the manufacturer approves the slab for floors, walls or outdoor use.
• Slip resistance: this matters for bathroom floors.
• Surface finish: polished surfaces show every unevenness and scratch.
• Spare material: allow extra for cutting and possible breakage, a little more than with ordinary tiles.
• Batch: all slabs should come from the same batch so the colour shade matches.

Look at the finished surface in daylight and also with a lamp held to the side, which shows up unevenness. At handover, go through this list:

• Edges of neighbouring slabs are flush, with no steps you can feel
• Slabs do not sound hollow when tapped, especially on the floor and in corners
• Joints are the same width and filled along their whole length
• Corners, the join with the shower tray and the edges around the bath are sealed with flexible silicone
• Movement joints are where they were agreed and are not filled with hard grout
• Cut-outs for taps, sockets and outlets are clean, with no chipped edges
• The surface is free of adhesive and grout residue
• There are no visible cracks or scratches
• You have been told which adhesive and grout were used, when the surface can take load and when the underfloor heating can be switched on