Grouting Wall and Floor Tiles

Why are tiles not simply laid tight against each other? No tile is perfectly accurate in size, and the surface underneath moves slightly as temperature and humidity change. The joint absorbs these differences. It also does several other jobs:

• It keeps water and dirt out so they cannot reach the adhesive and the surface behind the tiles
• It seals the surface so dirt does not collect in the gaps and mould struggles to take hold
• It helps spread loads and protects tile edges from chipping
• It shapes the look: the grout colour can make a surface look uniform or pick out the tile format

Keep in mind that ordinary cement grout is not waterproofing. In a shower and around a bath, there must be a waterproof layer behind the tiles, often called tanking. Grout only limits how much water reaches that layer.

The European standard EN 13888 divides tile grouts into cement-based grouts and reaction resin (epoxy) grouts. The packaging usually shows a class code, which helps you choose.

Cement-based grout

This is the grout used in the vast majority of homes. A basic grout is fine for dry areas with normal wear. For bathrooms, kitchens and floors, a grout with improved water and abrasion resistance (class CG2) is worth choosing. It is easy to work with and can be raked out and renewed later if needed.

Flexible cement-based grout

This suits any place where the surface underneath moves more: over underfloor heating, on terraces and balconies, with large-format tiles or on plasterboard. Added polymers help it cope with temperature changes and small movements without cracking.

Epoxy grout

Epoxy grout absorbs almost no water, resists chemicals and is easy to clean. People choose it for walk-in showers without a tray, kitchen splashbacks, commercial spaces with strict hygiene needs and mosaics. It is harder to work with, though. It sets quickly, needs a different cleaning method, and any residue that dries on the tiles is very difficult to remove.

Silicone for corners and joints between materials

The joint between wall and floor, internal corners, and the edges around a bath, shower tray and basin are not filled with cement grout. They get flexible sanitary silicone. In these places different materials move against each other, and a rigid grout would crack sooner or later.

1. Waiting for the adhesive: grouting starts only once the tile adhesive has set. With standard adhesives this is usually about one day, but the manufacturer gives the exact time.
2. Cleaning the joints: squeezed-out adhesive, spacers and dust are removed so the joint has the same depth along its whole length.
3. Dampening: with cement grout, absorbent tiles and joint edges are lightly dampened so they do not draw water out of the grout.
4. Mixing: the grout is mixed with exactly the amount of water stated in the instructions. Adding water by eye leads to colour differences.
5. Pressing in: a rubber grout float pushes the grout into the joints with diagonal strokes across the lines until they are completely full.
6. First wash: when the grout turns matt and no longer smears when touched, the surface is cleaned with a damp, well wrung-out sponge in circular or diagonal movements.
7. Removing the haze: once dry, a fine grey film stays on the tiles. It is buffed off with a dry cloth.
8. Silicone and aftercare: corners and junctions get a bead of silicone. Once cement grout has fully dried, it can be sealed.

Grouting varies in difficulty more than you might expect, and this affects how long the job takes and what it costs. These things usually make it slower:

• Mosaics and small tiles, where one square metre holds many metres of joints
• Textured and matt tiles, which take more effort to clean grout residue from
• Absorbent tiles and natural stone, which sometimes need pre-sealing so the grout does not stain them
• Contrasting colours, such as dark grout on light tiles, where every small flaw shows
• Epoxy grout, which needs quick, precise work in small sections
• Regrouting, where the old grout must first be raked out without damaging the tile edges

Large tiles with narrow, straight joints and smooth glossy wall tiles, on the other hand, are grouted fairly quickly.

• Grouting too early, before the adhesive has set and while the tiles can still shift
• Leaving adhesive in the joints, so the grout is too thin in places and cracks
• Using too much water when mixing or washing, which causes pale patches and soft joints
• Wiping along the joints, which drags grout out and leaves uneven grooves
• Using rigid grout in corners and around the bath instead of silicone
• Using several bags with different batch numbers without blending them together first

You can grout bathroom wall tiles or a kitchen splashback yourself if you have some patience. Start with cement grout and test it on an inconspicuous spot to see how quickly it turns matt.

1. Check the adhesive packaging to confirm the waiting time before grouting has passed.
2. Clean adhesive, spacers and dust out of the joints.
3. Cover the bath, shower tray and taps.
4. Mix a small batch of grout exactly as instructed and let it stand briefly.
5. Press the grout in with a rubber float, working diagonally across the joints over roughly one to two square metres at a time.
6. Wait until the grout turns matt, then clean the surface with a wrung-out sponge in circular movements.
7. Smooth the joints with the sponge or a rounded tool so they are all the same depth.
8. Buff off the grey haze with a dry cloth once it has dried.
9. Run silicone into the corners and junctions.
10. Avoid using the shower or walking heavily on the floor until the manufacturer allows it.

• Joints are full along their whole length, with no holes, bubbles or crumbling spots
• Depth and width are roughly the same everywhere
• The colour is even, without light or dark patches
• No haze or dried grout residue is left on the tiles
• Corners, internal angles and edges around fittings are filled with silicone, not cement grout
• The grout does not crumble when tapped or walked on
• You have been told when the room can be used and whether sealing is recommended