Why Grout Discolours So Quickly

Grout is porous, and that is both its strength and its weakness. The same tiny channels that help it grip tiles also trap soap scum, shampoo residue, body oils and the minerals in hard water. Add the warmth and humidity of a typical bathroom, and you have ideal conditions for the grey film and black speckles that appear along grout lines within months of a fresh regrout.

The good news is that most of this build-up sits on or just below the surface, which means it responds well to a simple, eco-friendly approach rather than harsh chemicals. Bicarbonate of soda is mildly abrasive, gently alkaline and completely biodegradable, which makes it the ideal partner for a stiff brush. Together they lift grime out of the grout rather than bleaching it into submission, and the result is brighter lines that stay brighter for longer.

Gather Your Kit and Keep It Together

Having everything within reach turns a fiddly job into a straightforward one. Assemble the following before you start:

• Bicarbonate of soda — a 500g box is plenty for a whole bathroom.
• Warm water in a small bowl or jug.
• A stiff-bristled grout brush, plus an old toothbrush for corners and the base of the shower screen.
• Microfibre cloths — two or three, so you always have a clean one for the final wipe.
• Rubber gloves and, if you are working overhead, a pair of safety glasses.
• Optional extras: a drop of washing-up liquid for greasy residue, a few drops of tea tree oil for its antifungal properties, and white vinegar for limescale.

Store these together in a small caddy or a labelled box under the sink. A kit that lives in one place is a kit you will actually use, and it stops half-used boxes migrating to the back of a cupboard. Keep a dedicated grout brush with the caddy so it never ends up doing duty on the oven.

The Bicarbonate Paste Method, Step by Step

Mix roughly three parts bicarbonate of soda to one part warm water in a small bowl. You are aiming for the consistency of thick toothpaste — firm enough to cling to a vertical grout line, soft enough to spread easily. If it crumbles, add water a few drops at a time; if it slumps, add more powder.

Work in manageable sections of about a square metre, starting at the far end of the wall and moving towards the door. Apply the paste along the grout lines with your fingers, a small spatula or an old spoon, pressing it gently into the grout rather than smearing it across the tiles.

Leave the paste in place for ten to fifteen minutes. If it begins to dry and crack, mist it lightly with water — the paste needs to stay slightly damp to do its work.

Now scrub. Use short strokes along the line rather than across it, which keeps the bristles in the grout channel and protects the tile edges. Apply firm but steady pressure; grinding hard with a wire brush can scratch glazed tiles and wear away coloured grout, so a stiff nylon brush is the safer choice.

Rinse thoroughly with warm water, wiping with a damp cloth as you go, then buff the tiles dry with a microfibre cloth. Rinsing properly matters — dried bicarbonate leaves a chalky white haze that can look worse than the dirt you removed.

Tackling Stubborn Stains and Mould

If a section refuses to shift, adjust the mix rather than the effort.

• Black speckled mould: add a few drops of tea tree oil to your paste and leave it for twenty minutes before scrubbing. Keep the extractor fan running or a window open while you work.
• Greasy build-up: add a single drop of washing-up liquid to the paste to help break down oils from shampoo and conditioner.
• Limescale around the shower: spray with white vinegar, leave for ten minutes, then scrub and rinse. Never use vinegar on marble, travertine or limestone, as the acid etches the surface.

Do not mix vinegar and bicarbonate in the same application — they neutralise each other on contact. Use one, rinse well, then use the other if it is still needed. Avoid bleach-based products on coloured grout, as they can strip the pigment and leave pale patches that no amount of scrubbing will restore.

Sealing Grout to Make Future Cleans Easier

Once the grout is clean and completely dry — allow a full twenty-four hours in a well-ventilated room — consider applying a grout sealer. Sealing fills the pores so that soap scum and water sit on the surface instead of soaking in. A single application can last six to twelve months, and it turns a deep clean into a quick wipe. Check the instructions on the tin, as drying times vary between products.

A Simple Routine That Keeps Grout Bright

Prevention is far less effort than correction. A few small habits make a real difference:

• After every shower: squeegee the tiles and leave the extractor fan running for ten minutes.
• Weekly: scrub the grout with a brush and warm soapy water as part of your usual bathroom clean.
• Monthly: apply a bicarbonate paste to the busiest areas — around the shower, bath and basin.
• Twice a year: carry out a full deep clean and check whether the sealer needs topping up.

Write these reminders on a small card and tape it inside the cupboard where your cleaning caddy lives, alongside your spare bicarbonate and brushes. Organised cleaning is simply cleaning you can start without thinking about it, and bright, mould-free grout lines are the reward for a routine that takes minutes rather than hours.