The tiles are clean, shiny, flawless. But the grout is dark. The grey lines that should be white or lime-coloured now look as if they haven't been cleaned for years. And perhaps they haven't. Grout is a porous material that absorbs everything — water, soap, oil, grease, mould spores. Once they turn dark, many give up because they think it takes hours of scrubbing with a brush. There are much easier methods — from simple DIY pastes to a steam cleaner that solves the problem in 20 minutes without any scrubbing.
Why do grout joints turn black?
Grout (the joints between tiles) is made from porous materials — cement, quartz sand, and pigment. This porosity makes it the perfect absorbent surface:
- Limescale from water that builds up and roughens the surface
- Soap and shampoo which leave behind grease and gunk
- Skin oils and perspiration
- Mould and fungus spores that develop in a damp environment
- Kitchen grease that clings to the rough surface
The result is a gradual darkening that is almost impossible to stop without impregnation — but which can be reversed with regular cleaning and the right method.
Types of grout and what it means for cleaning
| Grout type | Material | Sensitivity | Recommended method |
|---|---|---|---|
| Cement grout | Cement + pigment | Moderate | Steam, vinegar, soda |
| Epoxy grout | Epoxy resin | Low | Almost all methods |
| Mouldy grout | Silicone | High | Special anti-mould |
| Historical grout | Lime | High | Only gentle methods |
Method 1 — Bicarbonate of soda paste + hydrogen peroxide
The simplest and most effective DIY method for dark cement grout:
- Mix the bicarbonate of soda and 3% hydrogen peroxide into a paste (a ratio of approximately 2:1)
- Apply the paste to the grout with a small brush, a toothbrush or a gloved finger
- Leave for 10-20 minutes (for heavily discoloured grout, up to 1 hour)
- Scrub with an old toothbrush — minimal scrubbing is enough
- Rinse with warm water
Why does it work? Hydrogen peroxide oxidises organic stains and mould spores, bicarbonate of soda acts as a gentle abrasive and enhances the alkaline environment that breaks down fats.
Method 2 — Steam Cleaner (no chemicals)
This is the gold standard for grout. A Kärcher SC5 EasyFix or a similar steam cleaner with a grout brush attachment works wonders:
- Attaching the narrow brush attachment (special grout tool, included with the SC5)
- Steam at 130°C penetrates deep into the pores of the cement grout
- The heat softens deposits of grease, limescale and biological build-up
- The mechanical vibration of the brush (which spins under steam pressure) loosens the dirt
- Wipe with a microfibre cloth immediately after passing
Result: The grout lightens by 2-3 shades in 20-30 minutes of work, with no scrubbing and no chemicals. Especially effective for the bathroom (moisture, calcium) and the kitchen (grease).
Method 3 — White vinegar for limescale in grout
For white limescale deposits in the grout (a common problem in hard water areas such as Dugo Selo, Sesvete and the surrounding Zagreb area):
- Apply undiluted white vinegar to the grout
- Leave for 15-30 minutes (the vinegar dissolves the calcium deposits)
- Gently scrub with a brush
- Rinse with warm water
Caution: Do NOT use white vinegar on marble or stone tiles (the acid will damage the stone), or on lime-based grout. For ceramic and porcelain tiles — completely safe.
Method 4 — Commercial grout cleaners
When DIY methods aren't enough (deep mould, older grout, long-uncleaned):
- HG Grout Cleaner — one of the most effective commercial options, available at BauhausMethod 4 — Commercial Grout CleanersWhen DIY methods aren't enough (deep mould, older grout, long time since cleaning): Denkmit Fugen Reiniger — available at DM, for lighter stains HG Grout Cleaner — one of the most effective commercial options, available at Bauhaus
- Denkmit Fugen Reiniger — available at DM, for lighter stains
- Chlorine gel (e.g. Domestos gel) — for black mould in silicone; use with care, ensure good ventilation
Mould in grout — a particular problem
Black mould in grout (Cladosporium, Aspergillus) is not just an aesthetic problem — they are living organisms that release spores which are inhaled. Removal requires:
- Ventilation of the room (open a window, wear gloves and a mask)
- Apply a chlorine-based gel or anti-mould spray directly onto the mould
- Leave under cling film for 30-60 minutes (to prevent evaporation)
- Scrub and rinse
- Dry the surface (mould thrives in dampness)
After removing the mould, apply a grout impregnator that makes it waterproof and slows down future mould growth.
Sealing the grout — why it's crucial
Once the grout is clean, protect it with a sealer. Grout sealers (available from Bauhaus, OBI) penetrate the pores of the cement grout and create a hydrophobic layer:
- Water and oil no longer soak in — they simply bead up on the surface
- Mould has nowhere to anchor itself
- The grout is much easier to clean
- Effectiveness: 1-3 years
Apply with a brush or sprayer in 1-2 coats to completely dry grout. It's a cheaper and easier preventative measure than scrubbing annually.
How often to clean the grout?
| Room | Regularly | Deep clean |
|---|---|---|
| Shower cubicle / bath | Weekly (damp cloth) | Once a month |
| Toilet (tiles) | Weekly | Every 2-3 months |
| Kitchen (wall) | As needed (for immediate stains) | Every 3 months |
| Floor (bathroom) | Weekly | Every 2-3 months |
| Terrace / balcony | Once a week | Seasonal (spring) |
Local context
In Dugo Selo, Sesvete, Vrbovec, Brckovljani and Sveti Ivan Zelina, the water from the mains supply has a high hardness — which means that limescale in the grout builds up faster than in areas with soft water. Regular preventative treatment with vinegar or commercial anti-limescale products and the impregnation of grout are particularly important for households in this area. Hiring a Kärcher SC5 for the seasonal deep cleaning of bathrooms and kitchen surfaces is a popular option in this region.
Frequently Asked Questions (FAQ)
Can a steam cleaner damage grout?
On healthy, undamaged cement grout — no. Steam does not damage the grout if used correctly (not left on one spot for too long, not too high a pressure directly). Old and damaged grout (cracked, crumbling) can be further degraded by steam — in that case, it's better to replace the grout than to clean it. Silicone sealant — a quick pass is okay, but not prolonged direct contact.
Why are the grout joints in the shower always wet and mouldy?
The shower cubicle is the wettest spot in the house. The combination of heat and moisture several times a day creates perfect conditions for mould. The solution: after every shower, a quick wipe of the cubicle with a dry cloth or a squeegee, a fan or an open window for 20 minutes, and weekly cleaning with anti-mould products. A silicone and grout impregnator will dramatically slow the problem.
Can I refresh the grout by painting it without cleaning it first?
There is a special grout paint (available at Bauhaus) that can be applied with a brush to freshen up the grout colour. However, it only adheres to uncleaned grout, doesn't hold well, and starts to peel within 1-2 years. Proper cleaning and impregnation is a more permanent and cheaper solution.
Can bicarbonate of soda on its own (without peroxide) clean the grout?
Yes, but less effectively. Bicarbonate of soda is mildly abrasive and alkaline — it cleans surface grime. For deeper staining and mould, hydrogen peroxide is a key addition that oxidises and breaks down organic deposits. A paste of bicarbonate of soda and peroxide is more effective than bicarbonate of soda on its own.
How much does professional grout cleaning cost?
Professional grout cleaning with a steam cleaner for an average bathroom (6-10 m²) costs €30-€60. Alternatively, hiring a Kärcher SC5 (€40-€50/day) to clean the grout throughout your flat is a more economical option if you have multiple rooms.
Can I use bleach (chlorine) on cement grout?
Diluted bleach (1:10 with water) can refresh white cement grout, but with caution: ventilation is essential, wear gloves, do not mix with vinegar (it creates a toxic chloroacetic acid compound), and rinse thoroughly. Epoxy grout is chlorine-resistant. On marble and stone tiles — never.
What is the difference between grout and silicone?
Cement-based grout is used for the joints between tiles (horizontal and vertical surfaces). Silicone is used for corners, edges and joints where there is movement (the joint between a tile and a bath, shower enclosures, window frames). Silicone is flexible and waterproof, but it is more prone to mould. It is cleaned differently — mainly with anti-mould gels, not abrasives.
When is it better to replace grout than to clean it?
You should replace the grout when it is cracked (leaking water behind the tiles), crumbly (the cement is crumbling away), or when mould has penetrated so deeply that cleaning only removes the surface layer and the mould returns within a week or two. Refilling a bathroom-sized area costs €100–300 for materials and labour — but it's a one-off, long-lasting solution.
Conclusion
Cleaning grout doesn't have to be a chore. The right paste (bicarbonate of soda + peroxide) and the right equipment (a steam cleaner with a grout nozzle) can do in 30-60 minutes what scrubbing with a brush for hours can't. And a preventative impregnation treatment ensures the next clean will be significantly easier.
If you don't have the right equipment or simply want to leave the job to the professionals, there are solutions that can significantly speed up and make the whole process easier.