How to clean tile and floor grout until it is white again

What you need

• Stiff nylon grout brush (or an old toothbrush for corners)
• Bucket and mop
• Rubber gloves and safety glasses
• Spoon or plastic spatula for mixing
• Vacuum cleaner or broom
• Microfibre cloth
• Bicarbonate of soda
• 3 % hydrogen peroxide (chemist or supermarket)
• Alkaline grout cleaner such as Fila PS87 (Leroy Merlin, Bricodepot)
• Post-construction cleaner such as Fila Deterdek, only if there is a cement haze
• Anti-stain grout sealer such as Fila MP/90

Step by step

1. 1

   Sweep and vacuum the dust

   Remove dust and hairs from the grout channel with a vacuum cleaner. If you wet it while the dirt is still dry, it turns to mud and is harder to remove.

2. 2

   Test the product in a corner

   Pick a stretch of about 20 cm, for example behind the door or under a piece of furniture, and apply the cleaner. Wait 10 minutes and check that the tile does not lose its shine and the grout does not change colour.

3. 3

   Make up the paste

   In a cup, mix 4 tablespoons of bicarbonate of soda with hydrogen peroxide until you have a thick paste, like yoghurt. For years of dirt, replace the paste with the alkaline cleaner diluted as the label says.

4. 4

   Apply it one metre at a time

   Spread the paste over the grout with the spoon or with the brush itself. Work one metre at a time so that it does not dry before you scrub.

5. 5

   Leave it for 10-15 minutes

   Do not go beyond 15 minutes with strong alkaline products. The bicarbonate paste can stay for up to 30 minutes. Ventilate the bathroom in the meantime.

6. 6

   Scrub along the grout line

   Brush with medium pressure in the direction of the grout, not across it. The nylon brush is enough. On rustic floors or very wide joints you can use one with harder bristles. Go over the corners again with the toothbrush.

7. 7

   Treat mould separately

   If black marks remain, apply 3 % hydrogen peroxide or bleach diluted 1 to 5 with a cloth, leave it for 15 minutes and rinse. Never mix it with another product, and wear gloves and keep the room ventilated.

8. 8

   Rinse and dry

   Wipe over with a cloth and clean water, repeat twice and dry with microfibre. Leave the window open or the extractor fan running for an hour.

9. 9

   Seal the clean grout

   Once the grout is dry (wait 24 hours), apply the anti-stain sealer with a fine brush, leave it for 15 minutes and wipe off the excess with a cloth. Keep it dry for the next 24 hours.

Why grout gets dirty and what is behind each stain

Cement grout is porous. It soaks up water, grease and soap like a fine sponge, which is why it gets dirty long before the tile does. Before you buy anything, look at the colour of the stain, because each one needs a different product.

In the kitchen it is grease, which mixes with dust and forms a sticky brown film. In the bathroom it is black mould, especially in the shower and in corners with no ventilation. Limescale leaves a pale, rough veil. Rust turns grout orange near metal feet or a corroded drain. And in a flat that has just been refurbished, a grey cement haze left behind by the builders is perfectly normal.

Which product to use for which type of grout

First work out what grout you have. Most flats in the area have cement grout, 2 to 5 mm wide, which copes well with alkaline cleaners and badly with strong acids. Epoxy grout is more modern. You see it in refurbished bathrooms done with Mapei Kerapoxy or Litokol Starlike. It resists almost everything, but it stains if product residue is left on it.

For everyday cleaning, a neutral cleaner and a brush are enough. For a deep clean, a bicarbonate paste with a splash of hydrogen peroxide works in most cases and does not harm the grout. A dedicated cleaner, such as Fila PS87 or similar products from Leroy Merlin and Bricodepot, saves time when the dirt has built up for years.

On floors, the brush matters more than the product. A small-headed brush with stiff nylon bristles, the kind sold as a grout brush, gets into the channel without scratching glazed tiles. On polished porcelain or marble, always test in a corner first, because some products leave a mark.

Common mistakes when cleaning grout

• Mixing bleach with other products. With ammonia or with salfumán (hydrochloric acid, sold in every ferretería, or hardware shop) it releases toxic fumes. Use one product at a time and rinse well in between.
• Using salfumán on cement grout. It dissolves the cement. The grout looks whiter for a day and starts to crumble a few months later.
• Wire brushes or metal scouring pads. They scratch the tile and open up the pores of the grout, which then gets dirty even faster.
• Letting the product dry. If the cleaner dries on the grout, it stains again. Work in one-metre sections and rinse each section.
• Not drying afterwards. Damp grout in a bathroom with no window grows mould again within weeks. Go over it with a wrung-out mop or a cloth and open a window.
• Painting dirty grout. Grout pens and grout paint only stick to clean, dry grout, and they do not fix hollow grout.

When cleaning is not enough: regrouting and when to call someone

If the grout is still dark after two passes, the mould or grease is probably inside the material. The same goes if the grout sounds hollow when you tap it with a screwdriver, if it is cracking, or if you can see the tile adhesive underneath. In that case it has to be raked out and regrouted. Water gets in through broken grout and ends up loosening tiles or leaving a damp stain on the flat below.

At Manitas Costa regrouting a whole bathroom costs €150-300, replacing 1 to 5 loose tiles costs €60-120 and a builder's hourly rate is €30-40. If you only want us to check the bathroom and leave the kitchen and terrace grout clean, we can also do that on the handyman hourly rate. We normally give a fixed price over WhatsApp from a photo of the bathroom.

You can see everything we do on the small building works page, and the rates in how much a builder charges per hour. If old fixings have left holes between the tiles, see how to fill holes in tiles, and if the black stain is on the sealant and not on the grout, the guide on how to remove mould from the shower will help more.

Limescale, salt air and windowless bathrooms on the coast

In Valencia, Alicante, Torrevieja or Benidorm the tap water is usually hard and leaves limescale on grout and shower screens. If you clean the bathroom weekly with a mild product, the scale does not build up. If you leave it for months it hardens and is much harder to remove.

Interior bathrooms with no window, very common in buildings from the seventies and eighties, collect mould because they never dry out. A working extractor fan and leaving the door open after a shower do more than any product. In second homes that stay closed for months, the damp coastal air blackens the grout even if nobody uses the bathroom. Ventilate as soon as you arrive and clean before you sleep there.

Once the grout is clean and dry, an anti-stain grout sealer such as Fila MP/90 cuts absorption for a year or two. On terraces exposed to salt air, reapply it every season.