How to Grout Bathroom Tiles for a Durable Finish

Why Good Grouting Makes or Breaks a Bathroom

Grout has two jobs: it locks tiles together and it keeps water out of the substrate behind them. Done well, it gives you crisp lines that stay clean for years. Done badly — mixed too wet, packed in too thinly, or wiped away before it has firmed up — and you will be looking at crumbling joints, black mould creeping along the shower and tiles that start to sound hollow within a couple of winters. The reassuring part is that grouting rewards patience far more than skill. Work in small, manageable sections and you will get a finish worth showing off.

Cement-based grout is the standard choice in UK homes and comes in two broad types. Wide-joint (sanded) grout is for joints of roughly 3mm and above, so most floor tiles and larger wall tiles. Fine (unsanded) grout suits narrow joints of 1–3mm, typical of glazed wall tiles and mosaics. Epoxy grout costs more and is harder to apply, but it is practically non-porous and doesn't need sealing — a sensible upgrade for a busy family shower.

Preparation Before You Mix Anything

Grout is only as good as what it sits against, so do not rush this stage.

• Leave tile adhesive to cure fully — usually 24 to 48 hours, longer for thick-bed adhesive or in a cold room.
• Pull out all spacers and scrape any adhesive that has squeezed into the joints. Grout needs roughly two-thirds of the tile thickness to grip, and at least 2mm of depth.
• Vacuum the joints and wipe the tiles with a damp cloth to remove dust. Dusty joints give a weak bond.
• Check the room temperature. Most grouts want somewhere between 5°C and 30°C. A cold bathroom in February will slow everything down; a hot, draughty one will make the grout go off before you can wipe it.
• Have ready: a grout float, two buckets, a large grouting sponge, a microfiber cloth, a silicone smoother and clean water.

Apply in Small Sections and Push It In Firmly

Mix the grout to the ratio on the packet — by weight, not by eye — and aim for a consistency like thick toothpaste or peanut butter. Let it stand for five minutes, then stir again before use.

Now work in sections of about one square metre, roughly a third of a shower wall. This is the single biggest difference between a professional finish and a messy one. Apply the grout with the float held at about 45 degrees, dragging diagonally across the joints, then go over the same area at 90 degrees to fill any voids. It should feel like you are pressing the grout firmly into the gaps rather than smearing it over the surface.

Once a section is filled, scrape the float flat across the tiles to remove the bulk of the excess. Then move on to the next section — but only start cleaning when you have finished filling the area you mixed for.

Wiping Off: Timing Is Everything

Wait until the grout begins to firm up but has not set. Depending on temperature and humidity, that is usually 15 to 30 minutes. Test a small patch: if the grout holds its shape when you press it lightly, it is ready.

Use a sponge that is damp, not dripping. Wipe diagonally across the joints rather than along them, so you don't drag grout out of the gaps. Rinse the sponge often and change the water frequently — a second bucket of clean water makes this much easier. If you notice you are pulling grout out, stop and let it firm for another ten minutes.

A haze will remain on the tiles. Once the joints have hardened a little more, usually after an hour or so, buff it off with a dry microfibre cloth. Never leave that film overnight; it sets like cement and takes a lot of scrubbing to remove. Keep the room well ventilated but avoid direct heat, and leave the grout for at least 24 hours before it gets properly wet — ideally 48 in a shower.

Use Silicone Where the Room Moves

Grout is rigid, and bathrooms are not. Anywhere tiles meet a different material or change direction, use a silicone sealant instead:

• Internal corners where two tiled walls meet
• Where tiles meet the bath, shower tray, basin or floor
• Around window reveals and pipe collars

These are movement joints, and grout in them will crack. Choose a mould-resistant sanitary silicone in a colour that matches the grout, apply it to clean, completely dry surfaces, and smooth it with a silicone tool and a little soapy water for a neat bead.

Sealing and Keeping Mould at Bay

Cement grout is porous, which is why it stains and why mould gets a foothold. Once the grout has fully cured — usually 48 to 72 hours, or as the manufacturer advises — apply a penetrating grout sealer. If you have natural stone, unglazed porcelain or a porous matt tile, seal those too. Expect to re-seal shower areas every 12 to 24 months.

Day-to-day habits matter just as much. Run the extractor fan or open a window during and after showers, squeegee the walls, and dry the room rather than letting moisture sit. For cleaning, use a pH-neutral bathroom cleaner and a soft grout brush weekly. Avoid acidic limescale removers on cement grout, as they eat into it, and use bleach-based mould products sparingly. A paste of bicarbonate of soda and water lifts light staining gently.

If a joint does crumble or discolour beyond cleaning, rake out the affected grout to about 3mm, dust it out, and re-grout that section. Small, regular repairs are far cheaper than retiling.