How to remove mould from grout: the complete guide

The quickest reliable way to remove mould from grout is to spray 3% hydrogen peroxide directly onto the affected lines, leave it for 10–15 minutes, then scrub with a stiff nylon brush, rinse thoroughly and dry. Cleaning experts confirm that peroxide works as an oxidiser, penetrating porous grout to attack mould at the root rather than simply bleaching the surface stain. Finish by sealing the grout once it is fully dry.

Before you start:

Table of Contents

How to remove mould from grout step by step

Follow this sequence for a bathroom or kitchen. It works on ceramic and porcelain tiles; see the special-cases section below for natural stone.

  1. For stubborn stains, follow with a paste. Mix baking soda with a little water to form a thick paste, press it into the grout, and allow another 10–20 minutes. Alternatively, use an oxygen bleach powder (sodium percarbonate) paste for 20–60 minutes on deep-set staining.

Pro Tip: Spray peroxide the night before a deep clean and let it sit overnight on badly stained grout. The extended dwell time does a lot of the scrubbing work for you.

Which cleaner actually works on grout mould?

The short answer: peroxide and steam remove mould; bleach mostly hides it. Here is how the common options compare.

Cleaner Kills mould vs bleaches stain Risk to grout/stone Ventilation needed Dwell time Cost/availability in Australia Safe on natural stone or coloured grout?
3% hydrogen peroxide Kills mould at root Low Moderate Moderate dwell time Available at chemists and supermarkets Yes (test coloured grout first)
Household bleach (sodium hypochlorite, e.g. White King) Bleaches stain; often leaves roots Medium (can fade colour) High ventilation recommended Moderate dwell time Available at supermarkets and hardware stores No — avoid on coloured grout and stone
White vinegar (5% acetic acid) Light surface mould only Low on ceramic; damages stone Low ventilation needed Moderate dwell time Available at supermarkets No on stone; yes on ceramic/porcelain
Oxygen bleach paste (sodium percarbonate) Good on deep stains Low Low to moderate ventilation Longer dwell time recommended Available at hardware stores Generally yes; test first
Commercial mould removers (e.g. spray gels from Bunnings) Varies by formula Medium Moderate–high Per label — Check label
Steam cleaning Loosens grime; aids chemical treatment Very low Low N/A Hire or professional service Yes

A note on bleach: Bleach acts as a decolouriser on porous materials rather than a true fungicide. The roots stay in the grout and regrowth follows within weeks. It is fine for a quick cosmetic fix on white ceramic, but it is not a lasting solution.

Vinegar is genuinely useful for routine maintenance and light surface mould. Full-strength white vinegar handles limescale and early-stage mould well, but it struggles with entrenched black mould in porous grout.

Steam deserves more credit than it gets in DIY guides. Steam excels at loosening embedded soap scum and dirt before chemical treatment, which means your peroxide or oxygen bleach can actually reach the mould rather than sitting on top of a biofilm. A domestic steam cleaner from Bunnings or a professional steam extraction service takes this further.

What tools and supplies do you need?

Pick these up before you start. Most are available at Bunnings, your local chemist or a supermarket.

Cleaning agents:

Tools:

Safety gear:

After cleaning:

Optional: A domestic steam cleaner speeds up pre-cleaning. For a detailed walkthrough on using a steam cleaner on tiles and grout, the technique matters as much as the equipment.

Natural stone, coloured grout and silicone: where common cleaners fail

Not every surface tolerates the same treatment. Getting this wrong can cause permanent damage.

Natural stone (marble, travertine, limestone): Vinegar and any acid-based cleaner will etch the surface. Strong bleach can discolour and weaken the stone. Use only manufacturer-approved stone-safe cleaners and consult a professional if the mould is widespread. Hydrogen peroxide at 3% is generally considered safer than bleach on stone, but test an inconspicuous spot first.

Coloured grout: Chlorine bleach strips pigment. Stick to hydrogen peroxide or oxygen bleach methods, and always test in a hidden area before treating the full surface.

Silicone sealant and caulk: Surface mould on silicone can be cleaned with peroxide or a commercial mould spray. But if black staining keeps returning within a few weeks, the mould has penetrated behind the sealant. When mould has worked its way behind silicone, removing and replacing the sealant is the only lasting fix. Cleaning the surface repeatedly just delays the inevitable.

Black mould on silicone bathroom sealant close-up

Pro Tip: Before applying any cleaner to coloured grout or natural stone, test it on a small patch behind the toilet or under a shelf edge. Give it 15 minutes, rinse, and check for colour change or etching before committing to the full area.

When cleaning will not fix it: Cracked, crumbling or permanently discoloured grout, or mould that returns within two to three weeks of cleaning, signals that the grout itself is compromised. Regrouting or professional assessment is the next step, not another round of cleaning product.

How to stop mould coming back

Cleaning removes mould. Habits and sealing keep it away.

The Bunnings community forums consistently show that homeowners who combine peroxide treatment with regular squeegeeing and annual resealing see far less recurrence than those who rely on bleach alone.

When should you call a professional?

DIY works well for surface mould on intact grout. A few situations call for something more.

What professionals do differently: Commercial and truck-mounted steam extraction reaches deeper into grout pores than any domestic machine. Professionals also use oxidiser treatments at higher concentrations, assess grout integrity on the spot, and can regrout, remove failed silicone and apply commercial-grade penetrating sealers in a single visit. For a full picture of what professional tile and grout steam cleaning involves, the process is more thorough than most homeowners expect.

Cost and timeline: Small bathroom patches typically run a few hundred dollars; a full regrout or restoration job costs more and depends on area size and condition. The most reliable way to get an accurate figure is an on-site inspection and quote.

Pro Tip: If you are approaching end of lease, a professional grout clean is often cheaper than losing part of your bond over mould. Get a quote before you decide it is not worth it.

Safety details, dwell times and the full cleaning timeline

Never mix vinegar and bleach. The combination produces chlorine gas. Keep them in separate cleaning sessions with a thorough rinse between.

Product Recommended dwell time Key safety note
3% hydrogen peroxide 10–15 minutes Ventilate; avoid eye contact
Baking soda paste 10–20 minutes Low risk; rinse well
Oxygen bleach paste 20–60 minutes Moderate fumes; ventilate
Household bleach gel Moderate to longer dwell time recommended High fumes; strong ventilation essential; avoid on coloured grout

Drying and sealing timeline:

What to expect overall: A typical active cleaning session on a small shower or kitchen splashback takes 25–35 minutes, not counting dwell time. Add drying and sealing and you are looking at a two-day process from start to sealed finish. Severe jobs with deep staining may need a second treatment before the grout is ready to seal.

Key takeaways

Hydrogen peroxide (3%) is the most effective DIY treatment for mould in porous grout because it kills the mould at the root, not just the visible stain.

Point Details
Use peroxide, not bleach 3% hydrogen peroxide kills mould roots; bleach often only whitens the surface stain.
Dwell time matters Allow 10–15 minutes for peroxide; 20–60 minutes for oxygen bleach paste on deep staining.
Seal after every clean Apply a penetrating grout sealer once grout is fully dry; test annually and reseal when water stops beading.
Know when to stop DIYing Mould that returns within weeks, cracked grout or a musty smell behind tiles means it is time to call a professional.
Come for Melbourne jobs Carpet Team Melbourne provides tile and grout steam cleaning, regrouting and sealing across Melbourne when DIY is not enough.

Why tile pros reach for peroxide and steam before bleach

Bleach is the default choice for most people because it works fast and the result looks clean. The problem is that “looks clean” and “is clean” are not the same thing with porous grout. Bleach decolourises the stain at the surface but leaves the mould’s biological structure intact inside the grout pores. Within a few weeks, the same black lines are back, and the repeated bleach exposure gradually degrades the grout binder and fades any colour.

Hands scrubbing grout with peroxide and steam

Peroxide and steam take a different approach. Peroxide releases oxygen that oxidises the mould’s cellular structure, which is why it bubbles on contact. Steam physically dislodges the biofilm and soap scum that shields mould from chemical treatment, so whatever you apply afterwards actually reaches the problem. The professional workflow, steam first to open up the surface, then an oxidiser to treat the mould, then a sealer to close the pores, is more steps than a bleach spray but the results last considerably longer.

The other thing worth knowing: grout integrity matters more than the cleaner you choose. If the grout is cracked or the sealer has failed, no amount of surface treatment will stop moisture getting in and feeding new growth. Professionals assess this on every job and recommend epoxy grout or a full regrout when the substrate is too compromised to hold a sealer. That assessment is something a DIY approach simply cannot replicate.

Tile and grout cleaning in Melbourne when DIY has run its course

For surface mould on intact grout, the steps above will get you a long way. But when mould keeps coming back, grout is cracking, or you need a result you can guarantee before a rental inspection, a professional service is the faster and more reliable option.

Carpet Team Melbourne provides tile and grout steam cleaning, grout sealing and regrouting across Melbourne using commercial steam extraction and eco-friendly treatments. The difference from a DIY clean is extraction depth: truck-mounted equipment reaches the mould that lives below the surface, not just what is visible. Jobs that would take a homeowner a full weekend, including drying and resealing, are typically completed in a single visit.

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Renters approaching end of lease, homeowners dealing with recurring mould, and anyone whose grout is past the point of DIY repair can request a quote or book an inspection directly. An on-site assessment takes the guesswork out of whether cleaning, regrouting or silicone replacement is the right call.

Useful sources and further reading

The following references were used to compile this guide and are worth consulting for deeper reading or product-specific guidance.

For natural stone surfaces, always check the tile or stone manufacturer’s care guide before applying any cleaner. Product labels for sealers and oxygen bleach products carry specific application and cure times that vary by brand; follow them rather than general estimates.

This guide provides general information for homeowners and renters. For persistent mould, structural concerns or health-related issues, consult a qualified professional or your local council’s environmental health team.

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