Mosaic Tiling

The process is much like normal tiling, but the substrate and grouting need more care. The tiler first checks how flat the wall is. Small pieces follow every bump, and in side light every wave shows. That is why the wall is often levelled with a skim coat first.

In wet areas, such as the shower and around the bath, waterproofing comes next. This is usually a liquid or cement-based tanking membrane applied in two coats. Sealing tape goes into the corners, and collars go around the drain and pipe penetrations. Only then is the mosaic fixed. The adhesive is spread with a small-notch trowel so that it does not squeeze up into the joints. Each sheet is pressed in and lined up so the gaps between sheets match the joints within each sheet. If they do not, you will see a grid pattern across the wall.

Once the adhesive has set, the tiler grouts and cleans the surface. Finally, corners and joints where the mosaic meets another material are filled with silicone.

• Ceramic mosaic: The usual choice indoors. It is easy to cut and lay and suits bathroom and kitchen walls
• Porcelain mosaic: Harder and less absorbent. It works on shower floors, and outdoors if the manufacturer states it is frost resistant
• Glass mosaic: Handles water well and is used in showers and swimming pools. It is translucent, though, so the colour of the adhesive and any flaw beneath it show through
• Stone mosaic: Gives a natural look, but it absorbs water and is sensitive to acids. It needs sealing both before and after grouting

Glass mosaic is almost always fixed with a white flexible adhesive that the manufacturer recommends for glass. Grey adhesive would make the glass look dull and blotchy. Paper-faced mosaic goes on with the paper facing outwards. Once the adhesive has partly set, the paper is dampened and peeled off. Mesh-backed mosaic goes on with the mesh pressed into the adhesive.

For grout, the choice is between cement-based and epoxy. Cement grout is easier to work and fine for ordinary walls. Epoxy grout resists water, grease and mould better, so it is worth using in showers and behind kitchen worktops. It is harder to handle, though, and it sets quickly.

Mosaic is slower than laying large tiles, because the same area has far more joints and cuts. The main things that affect the effort, and so the cost, are:

• Condition of the wall: A flat, solid, dry wall saves time. Old flaking plaster or existing tiles need dealing with first
• Size and shape of the area: A small shower with many corners, a shelf and a niche takes more work per square metre than a plain wall
• Pattern: Single-colour sheets go up quickly. Colour blends, borders or pictures need planning and patience
• Material: Glass and stone are slower to cut, and glass needs special nippers or a wet saw
• Details: The fall towards the drain, edge trims, corners and mixer outlets

In a flat, let the building management or owners' association know in advance about noisy work and removing rubble. Tiling an existing wall does not normally need permission. If the job comes with bigger changes, such as moving a partition wall or relocating pipes, check with your local building authority first. Moving sockets in a kitchen splashback is a job for a qualified electrician.

• Fixing onto an uneven wall, so the surface looks wavy over time
• Missing or broken waterproofing in the shower, so water seeps through the joints into the wall
• Too much adhesive, which squeezes into the joints and later shows through or prevents proper grouting
• Grey adhesive behind glass mosaic
• Uneven gaps between sheets, leaving a visible grid
• Unsealed stone that soaks up coloured grout and stays stained
• Cleaning off grout too late, so the haze on glass is very hard to remove
• Rigid grout in corners instead of silicone, where cracks then appear

A handy homeowner can manage a small dry area, such as the splashback between the worktop and wall cupboards. A shower with waterproofing and a sloped floor is better left to a tiler. Before you start, switch off the circuit breaker for any sockets in the wall, and have an electrician remove and refit the sockets themselves.

1. Remove grease and dust, then check the wall is flat with a straightedge.
2. Fill any unevenness with a skim coat and let it dry as the manufacturer says.
3. Apply a primer that suits the adhesive you are using.
4. Lay the mosaic out on a table and plan it so the cuts fall in less visible places.
5. Mark a level line to start from.
6. Spread adhesive with a small-notch trowel over an area for about two or three sheets.
7. Press a sheet in, tap it flat with a rubber float and check the gaps to the neighbouring sheets.
8. Clean any adhesive out of the joints while it is still fresh.
9. Let the adhesive set as stated on the pack, usually at least one day.
10. Work the grout in with a rubber float held diagonally to the joints, and after a short while wipe with a damp sponge.
11. Once dry, buff off the haze with a dry cloth and seal the joint with the worktop using silicone.

• The surface looks flat in side light, with no pieces sticking out
• Joints are the same width within the sheets and between them, with no visible grid
• Joints are fully filled, with no pinholes or sunken spots
• No grout haze or stains are left on glass or stone
• No adhesive streaks or empty patches show through glass mosaic
• Tapping does not reveal any hollow-sounding areas
• Corners and joints with the bath, shower tray or worktop are filled with silicone
• In the shower, water runs to the drain and does not pool anywhere
• Stone mosaic has been sealed, and you have been told which cleaning products are safe to use