You clean the shower every week. You have tried the spray with the skull on the bottle, the bleach pen, the electric scrubbing brush and the toothbrush and bicarb method from TikTok. The grout goes lighter for about four days. Then it is grey again, and the corners are creeping back to black.
This is not a cleaning failure. It is a materials problem, and understanding it explains why you have been fighting a battle that cannot be won with a spray bottle.
What Grout Actually Is
Standard bathroom grout is cement based. Cement is porous, riddled with microscopic capillaries that draw in water like a sponge. It is also alkaline and mineral rich, which happens to be an excellent environment for mould.
So the material lining every joint in your shower is, by design, absorbent and hospitable to the exact thing you are trying to remove. In a Sydney bathroom that sees two or three hot showers a day, often with a window that stays shut and an exhaust fan venting into the ceiling cavity rather than outside, the grout barely dries between uses.
The Four Things Turning Your Grout Dark
1. Mould Growing Inside the Grout, Not On It
This is the big one. When you bleach the surface you are not killing the colony, you are bleaching the pigment out of the top layer of it. The colony itself is alive and well two millimetres deep, and it recolours within days. That is exactly why bleach appears to work and then does not.
2. Soap Scum and Body Oils
Soap reacts with minerals in Sydney’s water supply to form a waxy film that binds into the porous grout surface, going progressively grey and holding onto dirt.
3. Efflorescence
White or chalky deposits, usually along shower bases and lower joints. These are mineral salts carried through the grout by moisture and left behind as the water evaporates. Efflorescence is a symptom of water moving through the substrate, which usually means water is getting somewhere it should not be.
4. Failed Waterproofing Beneath the Tiles
This is the one nobody wants to hear. If your grout is crumbling, permanently dark, or staining in patterns that ignore the actual shower spray zone, the waterproof membrane under the tiles may have failed. No amount of surface work resolves that.
Why Sydney Bathrooms Are Particularly Bad For It
Coastal humidity, mild winters and a lot of housing stock with poor bathroom ventilation combine badly. Apartments are the worst offenders, with small internal bathrooms, a single ducted fan that is often shared, and no operable window at all. Add a family of four showering back to back and the tiles genuinely do not dry between uses.
Older Eastern Suburbs and Inner West homes bring a second issue. Bathrooms renovated in the 1980s and 1990s were waterproofed to standards that no longer apply, and those membranes are now well past their service life.
What Actually Fixes It
There are three legitimate solutions, and the right one depends entirely on the condition of the grout. This is why an onsite assessment matters more than a quote over the phone.
Deep Cleaning and Sealing
If the grout is structurally sound and simply dirty, professional shower cleaning genuinely restores it. This uses heat and controlled pressure to flush contaminants out from deep inside the grout lines, pulling soiling out of the pores rather than scrubbing the surface. Once clean and fully dry, a penetrating grout sealer slows future absorption.
Best suited to discoloured but intact grout with no crumbling and no movement. It typically holds for two to four years before resealing.
Grout Colour Sealing
A pigmented coating bonded over the existing grout, sealing the pores and delivering a uniform colour. It is effectively a permanent membrane across the joint, and it lets you change colour entirely. Going darker to hide future soiling is a popular choice in family bathrooms.
Best suited to sound grout with uneven or permanent staining.
Epoxy Regrouting
The old grout is mechanically removed from the joints and replaced with epoxy grout. Epoxy is a resin rather than a cement, which makes it essentially non porous. Water cannot penetrate it, so mould has nothing to colonise and nothing to feed on inside the joint. This is what our grout replacement service is built around, and it is the only option that ends the cycle rather than resetting it.
Best suited to crumbling, missing, cracked or repeatedly failing grout.
What Does Epoxy Regrouting Cost in Sydney?
Indicative ranges for a standard shower recess:
- Deep clean and seal, roughly $350 to $700
- Grout colour sealing, roughly $600 to $1,200
- Full epoxy regrout of a shower, roughly $900 to $1,800
Wall and floor tiles throughout a full bathroom sit higher. The variables that move the price are tile size, since more joints per square metre means more labour, along with the condition of the existing grout, access, and whether the silicone in internal corners and around the base needs replacing. It almost always does, and any quote that leaves it out is incomplete.
For context, a full bathroom renovation in Sydney starts somewhere around $18,000 to $25,000. A bathroom rejuvenation resolves the same visual problem for a fraction of that, which is why we often talk people out of the renovation they arrived assuming they needed.
What Will Not Fix It
- Bleach, which only bleaches the surface and degrades cement grout with repeated use, accelerating the crumbling
- Grout pens, which are a paint layer over the problem and peel within months in a wet area
- Grout reviver sprays, which are cosmetic and short lived
- Silicone applied over failing grout, which traps moisture behind it and makes the underlying problem worse
Keeping It Clean Afterwards
Run the exhaust fan for twenty minutes after every shower. Squeegee the walls, which takes fifteen seconds and removes most of the water that would otherwise sit in the joints. Leave the shower screen open to allow airflow. Use a pH neutral cleaner rather than an acidic bathroom spray, especially if you have stone tiles rather than ceramic. Stone showers also benefit from proper sealing and protection once restored.
Frequently Asked Questions
Why does my grout go black again after I bleach it?
Because bleach only removes the colour from the top layer of the mould. The colony lives inside the porous grout, well below the surface, and it recolours within days. Bleaching treats the symptom and never the cause.
Is epoxy regrouting worth the extra cost?
For a shower that keeps failing, yes. Epoxy is non porous, so mould cannot grow inside the joint and the problem does not return. Cement based repairs restart the same cycle, which usually means paying again in a few years.
Can mouldy grout be repaired without retiling?
In most cases, yes. Regrouting removes and replaces the grout while leaving the tiles in place. Retiling is only necessary where tiles are drummy, cracked, or the waterproof membrane beneath has failed.
How long does shower regrouting take?
A standard shower recess is usually a one to two day job depending on the method. Showers generally need to stay dry for a short curing period afterwards, and we confirm that window at the time of quoting.
Is black mould in grout a health risk?
Persistent mould in a poorly ventilated bathroom can aggravate respiratory conditions and allergies. It is also a reliable indicator of a moisture problem that will keep worsening until the source is addressed.
The Bottom Line
Grout discolouration is not a sign that you clean badly. It is the predictable result of putting a porous, alkaline material into the wettest room in the house. Surface cleaning resets the clock. It never stops it.
The right fix depends on what is happening beneath the surface, which requires eyes on it. Complete Stone Care assesses Sydney bathrooms at no charge and tells you plainly which of the three options your bathroom actually needs, including the times when the answer is the cheapest one. Honest upfront pricing, no dust, no mess and prompt Sydney wide service.
