Mould
A living growth, not a stain. Killing it and removing the staining are two separate jobs, and neither addresses the moisture that caused it.
Precautions
- Ventilate the area
- Consider professional help
In detail
Mould is a fungal growth that establishes where there is persistent moisture, and treating it as a stain is the reason it so often returns. Three distinct things are involved. There is the living growth, which a disinfectant can kill. There is the pigment it has deposited, which may remain as a dark mark on grout or sealant after everything living is dead, and which needs a bleaching agent rather than a disinfectant. And there is the moisture that allowed it — condensation, a leak, poor ventilation — which no cleaning product addresses and which guarantees recurrence if it is not fixed. On porous materials such as silicone sealant or grout, growth extends below the surface, so a treatment that visibly clears the surface may leave viable material beneath. Extensive or repeatedly returning mould, particularly where it may indicate a building fault, is a case for professional assessment rather than a stronger cleaner. One removal instruction inverts the obvious move: an extension service permits surface mould on hard flooring to be taken up with a HEPA VACUUM and says explicitly NOT to use a standard one. On leather it brushes the spores off DRY first, before anything wet.
What works
Ammonia is effective against Mould Supported
Named by the stone trade for biological staining, with an emphatic warning never to combine it with bleach.
Sodium hypochlorite (chlorine bleach) is effective against Mould Disputed
THE SOURCES DISAGREE, AND THE DISAGREEMENT IS THE ANSWER. All of them put moisture control first and physical removal with detergent second; where they part company is whether a bleach step afterwards is worth adding, and at what dilution.
Mild abrasion is effective against Mould Supported
A stiff brush, hot water and household detergent. The mechanical part is the part that does the work, and the authorities say so in that order.
Mould remover is effective against Mould Supported
It removes the stain reliably and does nothing about the reason the growth is there.
Moisture control is effective against Mould Strongly supported
Dehumidifier is effective against Mould Supported
Detail brush is effective against Mould Supported
Why
- Mould is explained by Porous and non-porous surfaces
- Mould is explained by Moisture control and recurrence
Three authorities, same ordering, and none of them starts with a product. The reader asking which spray to buy has asked the second question first.
- Mould is explained by Cleaning, sanitising and disinfecting
The single most load-bearing sentence in the mould family: DEAD MOULD MAY STILL CAUSE ALLERGIC REACTIONS, so it is not enough to kill it — it must also be REMOVED.
- Mould is explained by Organic load
- Mould is explained by Surface roughness
Aftercare and prevention
- Rinsing and drying helps prevent Mould
With a deadline attached: water-damaged materials are dried within 24 to 48 hours, after which the question stops being how to clean and becomes what to remove.
- Dry soil removal helps prevent Mould
The manufacturer's own explanation of why its fabric resists mildew: the fabric does not promote growth, and the mildew grows on the DIRT left on it. Remove the dirt and there is nothing to grow on.
- Moisture control helps prevent Mould
- Dehumidifier helps prevent Mould
Hacks and claims involving this
- Spraying hydrogen peroxide and vinegar in sequence Does not work
- Following bleach with an alcohol sanitiser Does not work
- Vinegar as an all-purpose cleaner Disputed
- Steam cleaning sanitises without chemicals Unresolved
- Using a limescale remover on shower grout Does not work
- Mould needs bleach Does not work
- A hot empty wash cleans the machine Unresolved
- Leaving the washing machine door open Plausible mechanism, untested in this application
- Steam mopping a laminate floor Does not work
- Putting a cleaning block in the cistern Does not work
- Combining bleach and hydrogen peroxide Does not work
- Bleach ruins outdoor fabric Does not work
- Running bleach through a washing machine to clean it Disputed
- Borax for mould Unresolved
- One spray for the whole bathroom Does not work
- Freezing kills mould Does not work
- Killing the mould solves the problem Does not work
Where the sources disagree
Should chlorine bleach be used on household mould, and at what dilution?
Read side by side these bodies agree on far more than the disagreement suggests, and the agreement is the useful part. All three put MOISTURE CONTROL first and say the growth returns without it. All three make PHYSICAL REMOVAL with detergent and water the actual method. None presents bleach as the way mould is cleaned. What they differ on is whether an optional kill step afterwards earns its place — and the answer tracks the WATER, not the mould. Where the water was clean, the bleach step is merely offered and the federal guide declines to recommend it; where it was floodwater or sewage, both bodies that give dilutions positively recommend it, because the concern has shifted from mould to what else the water carried. The federal guide's reason for declining is not that bleach fails: it is that killing without removing leaves an allergenic residue, and that a background level of spores is normal once the area is dry.
What to do: Fix the water first — every source says the mould returns otherwise. Then remove the growth physically, scrubbing hard surfaces with detergent and water and drying completely; that is the method all three bodies give. Porous material that has grown mould — carpet, plasterboard, insulation, ceiling tiles — is discarded rather than treated, on every source. If you add a bleach step on a hard surface afterwards, that is a position two public bodies support and one declines to recommend; use the conditions they all agree on: dilute, ventilate, gloves and unvented eye protection, and never mix bleach with ammonia, with acids such as vinegar, or with any other product. Mould over about ten square feet, or after flooding or sewage, is not a cleaning job.
The sources are answering different questions
Sources for this page
Sources
Working with substances hazardous to health: A brief guide to COSHH
Health and Safety Executive (HSE), United Kingdom · Government or regulator
Relied on for: That ventilation is treated as a primary control measure when working with hazardous substances.
Removing Mold in Your Home, publication C 1047-2
University of Georgia Cooperative Extension, 2023 · Credible secondary source
Relied on for: That surface mould on hard flooring may be vacuumed with a HEPA vacuum and that a standard vacuum must NOT be used, and that mould on leather is brushed off dry with a soft brush or cloth before cleaning with water and non-phosphate detergent. (states this directly)