The short answer: Before you apply anything, establish the type of joint – because what helps one destroys another. Cement joints are cleaned alkaline (baking-soda paste, grout cleaner) and never permanently with acid, which dissolves the cement. Acrylic joints are open-pored and delicate: only mild, without scouring agents, without chlorine – they can usually be cleaned only to a limited extent and have to be replaced. Silicone joints need yet another treatment. And concrete joints outdoors do not tolerate a pressure washer, which flushes them out.
First: which joint do you have in front of you?
This is not an academic question. The four common types of joint react completely differently to cleaning agents, and the most frequent damage arises from treating them all the same.
| Type of joint | How to recognise it | Where it is found |
|---|---|---|
| Cement joint (mortar joint) | hard, mineral, fingernail does not penetrate | between all tiles across the surface |
| Epoxy resin joint | hard, slightly glossy, very smooth | commercial, wet areas, swimming pool |
| Silicone joint | rubbery, elastic, glossy | corners, connection of bathtub and floor |
| Acrylic joint | elastic, but matt and dull | connection to wall, ceiling, door frames |
The simplest test: press with your fingernail. A cement or epoxy joint does not give way. An elastic joint gives way – if it is glossy and rubbery, it is silicone; if it is matt and dull, it is acrylic.
The distinction between silicone and acrylic is the most important, because it is the one most often got wrong and the consequences are the greatest.
Cement joints: alkaline, never acid
Cement joints are mineral and absorbent. They take up dirt, grease and dyes – and because they lie lower than the tile, everything that gets moved when wiping collects there.
The decisive point: Cement joints must not be treated permanently with acid. Vinegar, citric acid and acidic sanitary cleaners attack the cement stone. The joint first becomes lighter – which looks like a cleaning success –, then sandy, then crumbly. In the end it crumbles out.
What works instead:
Baking-soda paste. Mix baking soda with a little water into a paste, work it into the joint with an old toothbrush or a grout brush, leave it for ten minutes, brush off and rinse. The combination of mild alkalinity and light abrasive action is ideal for cement joints.
Alkaline grout cleaner. On large areas and heavy soiling faster and more effective than any home remedy. For commercial use the right choice anyway, because otherwise the working time exceeds the material price many times over.
Steam cleaner. Harmless and effective on cement joints, because heat and moisture loosen the dirt without chemicals being necessary. Work with a point nozzle and wipe the joint dry afterwards.
The right brush. A grout brush with a narrow head reaches the depth of the joint, a flat mop does not. For floor joints a brush with a handle is worthwhile – working on your knees is the main reason why it is done too seldom.
When cleaning is no longer enough
Cement joints have a limited life. If the coating is no longer on the surface but has gone deep, cleaning is time lost. Then there are two routes:
Cosmetic: A grout pen or grout paint covers the discoloured surface. Depending on the load that lasts one to three years and, with joints that are otherwise intact, is a legitimate interim solution.
Fundamental: Scrape the joint out a few millimetres deep and grout again. More laborious, but the result is like new – and with crumbly, washed-out joints the only right answer anyway, because there the function is no longer given either.
Acrylic joints: the most difficult case
Acrylic is used readily because it can be painted over and costs less than silicone. The price for that is the surface: it is matt, microporous and takes up dirt instead of repelling it. This is precisely why a dirty acrylic joint is so thankless.
What you can do: mild washing-up liquid in warm water, a soft cloth or a very soft brush, gentle pressure. Then wipe dry.
What you should not do:
| Agent | What happens |
|---|---|
| Chlorine, bleach | Acrylic yellows and becomes brittle |
| Scouring agents, hard brush | tears the surface open, afterwards it gets dirty faster |
| Acid | attacks the surface, makes it dull and rough |
| Solvents, acetone | attack the material |
| Steam cleaner | softens the joint, edges come away |
| Long soaking | Acrylic is not waterproof, it swells |
The honest answer: A deeply soiled or yellowed acrylic joint can no longer be got clean. The dirt does not sit on the surface but in it. There replacement is the only way – and with acrylic that is uncomplicated, because the material can be cut out easily.
Important to know: Acrylic does not belong in permanently damp areas. It is not water-resistant and not mould-resistant. An acrylic joint at the edge of a bathtub or in the shower was the wrong product from the start – sanitary silicone belongs there. If, when cleaning, you find acrylic at a wet-area connection, replacing it with silicone is the right consequence.
Yellow joints in the shower
One of the most frequent questions – and the answer again depends on the type of joint.
With cement joints yellow is almost always lime soap: the compound of limescale in the tap water and fatty acids from shower gel and soap. It dissolves alkaline. Work in baking-soda paste, leave it, brush off. Limescale haze on the surrounding tiles you can afterwards remove acidic – but then deliberately on the tile and not in the joint.
With silicone joints yellow is either lime soap on the surface or yellowing of the material itself. The one goes away, the other does not. Details are in the instructions for cleaning silicone joints.
With acrylic joints yellow is usually yellowing of the material. That is irreversible.
Black spots, by the way, are something different from yellow discolouration: that is mould, and it is not brushed but treated with a suitable agent. Scouring merely spreads the spores.
Concrete joints and paving joints outdoors
Outdoors the task changes: instead of lime soap and grease it is about green deposits, moss, soil and leaf residue.
No pressure washer on paving joints. The jet flushes the joint material out. What follows is foreseeable: the stones lose their lateral support, wobble, shift, and in the empty joint the weeds grow even faster in the next spring. The re-sanding is considerably more work than the cleaning saved.
What works instead: a scrubbing brush or a joint scraper for the rough work, then hot water. With green deposits, a green deposit remover that is applied to the surface and left to act – the result sets in over days, not immediately.
What you must not use: salt, vinegar and weedkiller on paved surfaces. On sealed surfaces that is not permitted without approval, because the agents reach the sewer system and the groundwater unfiltered. Fines for it are not rare.
The actual cause is usually standing wetness. Where water can run off, considerably less settles: check the slope, keep drains clear, consistently remove leaves in autumn.
Epoxy resin joints: easy to care for, but sensitive to mechanical action
Epoxy resin joints are found in commercial kitchens, swimming pools, laboratories and increasingly in private bathrooms too. They are chemically resistant, absorb hardly any water and get dirty considerably more slowly than cement joints – that is their advantage.
Their weak point is the surface. It is smooth and slightly glossy, and it is precisely this gloss that is lost through scouring agents and hard brushes. An epoxy joint scoured matt afterwards takes on dirt that it would previously have repelled.
For cleaning, a neutral or slightly alkaline cleaner with a soft cloth is as a rule enough. Acid is unnecessary – the joint contains no limescale that would need dissolving. What does stubbornly persist with epoxy joints, on the other hand, are application residues from the construction period: a fine resin haze on the tile next to the joint. It cannot be removed with household means and needs a special epoxy remover.
Regrouting: when it is worthwhile
At some point cleaning is the wrong answer. These signs speak for replacement rather than the next attempt at cleaning:
| Finding | Meaning |
|---|---|
| Joint turns to sand when scratched | Cement stone is destroyed – regrouting |
| Joint lies lower than before | washed out, usually through acid |
| Cracks along the joint | Movement in the substrate – clarify the cause |
| Hollow sound when tapped | Tile is coming loose, not just the joint |
| Mould keeps coming back | Moisture behind the joint |
| Discolouration sits deep in the material | Cleaning no longer achieves anything |
With a cement joint, to regrout the old joint is scraped out a few millimetres deep – by hand with a joint scraper or by machine with a grout cutter. Then vacuum thoroughly, dampen the flanks and slurry in anew.
The decisive point is the depth. Anyone who only reworks the surface gets a thin layer that breaks out again at the first wipe. As a rule of thumb the new joint should be at least as deep as the joint is wide.
With elastic joints the procedure is different: they are cut out completely, the flanks cleaned and dried, and then a new joint is run. What matters is the complete removal of the old material – the new joint does not adhere to remains. The dimensions and technique for this are in the instructions on joint width and joint depth.
What does not work – even though it says so everywhere
The classic home-remedy lists for joints regularly contain three recommendations you can save yourself.
Toothpaste. Contains mild abrasive particles and surfactants – so it does work a little, but no better than baking soda, and it leaves residue that has to be washed off again. The only real advantage is the smell.
Nail polish remover. Acetone attacks plastics and is ineffective against mineral dirt. On silicone, acrylic and plastic profiles it does damage.
Ammonia solution. Strongly alkaline, but a health concern in a small bathroom. An alkaline grout cleaner does the same without the fumes.
So that joints stay clean longer
Joints get dirty first because they are rougher and lie deeper than the tile. Three habits make the biggest difference:
Squeegee after showering. Where there is no standing water, no lime soap forms – neither on the tile nor in the joint.
Ventilate until the surface is dry. That is the most effective measure against mould in the joints, full stop.
Impregnate cement joints. A joint impregnation reduces absorbency considerably. It is not permanent protection and has to be renewed after some years, but it noticeably lengthens the time between two deep cleans. It makes sense directly after regrouting or after a successful deep clean.
For the appropriate cleaning of the tile surfaces themselves – and why acid and alkaline must not be mixed up – there is a separate article.
Frequently asked questions
How do you clean acrylic joints?
Only mild: warm water with a little washing-up liquid, soft cloth, gentle pressure. No chlorine, no acid, no scouring agent, no steam cleaner and no long soaking – acrylic is not waterproof and swells. Deeply soiled or yellowed acrylic joints can no longer be rescued and have to be replaced.
How do heavily soiled tile joints become white again?
With cement joints with baking-soda paste or an alkaline grout cleaner and a grout brush, if necessary with the steam cleaner. If the dirt sits deep in the material, the only remedy is a grout pen as a cosmetic fix or scraping out and regrouting.
May I use vinegar on tile joints?
Better not. Acid attacks the cement stone – the joint becomes lighter in the short term, sandy and crumbly in the long term. For cement joints alkaline agents are right; acid belongs on the tile if limescale sits there, not in the joint.
Can I clean joints with the steam cleaner?
With cement joints yes, that works well and without chemicals. Not with silicone and acrylic joints – heat and pressure soften the material and loosen the edges.
What helps against yellow joints in the shower?
With cement joints it is usually lime soap, which dissolves alkaline: work in baking-soda paste, leave, brush off. With silicone and acrylic joints the discolouration can lie in the material itself – then the only remedy is replacement.
How do you clean concrete joints outdoors?
Mechanically with a scrubbing brush or joint scraper, then hot water or a green deposit remover. Under no circumstances with the pressure washer, which flushes the joint material out – after that the stones lose their support. Salt and vinegar are not permitted on paved surfaces.
How do I tell whether my joint is silicone or acrylic?
Both give way under finger pressure. Silicone is glossy and feels rubbery, acrylic is matt and dull. A second indication: acrylic can be painted over and is therefore often covered with paint at connections to painted components.
Is a joint impregnation worthwhile?
With cement joints yes. It reduces absorbency considerably and lengthens the time between two deep cleans. The best time is directly after regrouting or after a successful deep clean – applied to dirty joints it seals the dirt in.
How deep do I have to scrape out when regrouting?
As a rule of thumb at least as deep as the joint is wide. Anyone who only reworks the surface gets a thin layer that breaks out again at the first wipe. After scraping out, vacuum thoroughly and dampen the flanks.
How do I clean epoxy resin joints?
With a neutral or slightly alkaline cleaner and a soft cloth. Acid is unnecessary because there is no limescale to dissolve, and scouring agents remove the gloss – an epoxy joint scoured matt gets dirty faster afterwards than before.
