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Mould after water damage: the 48-hour window

Mould can start within a day or two of a leak. Why drying speed matters, the health risks, what you can clean yourself and when to bring in a remediation specialist.

Mould is the hidden cost of water damage. You deal with the obvious wet carpet, then weeks later the smell and the black spots arrive behind the skirting. The way to avoid that is to understand how fast mould moves and to dry the building out before it gets a foothold.

How fast it starts

Given moisture, warmth and something organic to feed on, mould spores can germinate and start colonising within 24 to 48 hours. Australia's warm, humid climate, and Sydney's coastal humidity in particular, speeds this up. That 48-hour window is why professional restorers push so hard on rapid extraction and structural drying rather than surface mopping.

The health side

Mould exposure can trigger runny noses, sneezing, coughing, wheezing and eye irritation, and it can be worse for people with asthma, allergies or weakened immune systems, and for infants and the elderly. Victorian and Queensland health authorities advise anyone in these groups to stay away from mould cleanup. There is no safe way to leave a significant mould problem untreated in a lived-in home.

What you can handle, and what you cannot

Small patches of surface mould on hard, non-porous surfaces can often be cleaned with detergent and water, then dried thoroughly. Wear gloves and a mask. Porous materials that have been wet for more than about two days, such as carpet underlay, plasterboard, mattresses and soft furnishings, usually cannot be fully decontaminated and are best removed.

Dry the space aggressively: open windows and doors, run fans and use an air conditioner or dehumidifier. The goal is to get materials and the air dry, because mould cannot grow without moisture.

If the affected area is large, if the water was greywater or sewage, or if mould keeps returning after cleaning, bring in a professional mould remediation and water damage specialist. They can find moisture trapped inside wall cavities and subfloors that a visual check misses, and dry it out before it spreads.

Sources

• Queensland Health, Mould after a disaster
• Victoria Department of Health, After a flood: mould and your health