Mould After Flooding: What to Do in the First 48 Hours

When floodwater enters your home, mould is not a possibility — it is an inevitability unless you act fast. Mould spores are always present in the air. All they need is moisture and an organic surface, and they will begin colonising within 24 to 48 hours. After 72 hours, mould growth can become extensive and far more costly to remediate.

The first 48 hours after flooding are critical. Here is exactly what to do.

Why speed matters

Mould does not wait. Under the right conditions — warm temperatures, high humidity, and a food source like plasterboard, timber, or carpet — mould spores germinate and begin forming colonies within a single day.

After 48 hours, mould can:

• Penetrate deep into porous building materials
• Spread behind walls and under flooring where you cannot see it
• Begin producing mycotoxins (depending on the species)
• Cause structural degradation of timber and plasterboard
• Create airborne spore levels high enough to cause respiratory symptoms

Every hour of delay increases the scope — and cost — of remediation.

Immediate steps: the first 24 hours

1. Ensure safety first

Before re-entering a flooded property:

• Turn off electricity at the mains if the switchboard is accessible and dry. If not, call your electricity provider
• Wear protective gear — rubber boots, gloves, an N95 mask, and eye protection. Floodwater carries bacteria, sewage, chemicals, and debris
• Check structural integrity — do not enter if walls are bulging, floors are buckling, or the building appears structurally compromised
• Photograph everything before you start cleaning. This is essential for insurance claims

2. Remove standing water

Get water out as quickly as possible:

• Use a submersible pump for significant standing water
• Wet/dry vacuums work well for smaller amounts
• Mop and bucket for the remainder
• Open doors between rooms to allow drainage

If the flooding is severe, contact a water damage restoration company. They have industrial-grade extraction equipment that can remove water far faster than domestic tools.

3. Remove wet contents

Move items out of the flooded area promptly:

• Furniture — move to a dry area or outside to dry. Lift wooden furniture off wet carpet to prevent staining and further water absorption
• Rugs and loose carpet — pull up and take outside. Rugs that have been saturated with floodwater (especially stormwater or sewage) are generally not salvageable
• Soft furnishings — cushions, curtains, and upholstered items saturated with contaminated water should be discarded
• Electronics — do not attempt to turn on any electronics that were submerged. Let them dry completely and have them assessed by a technician

4. Start air circulation

Get air moving immediately:

• Open all windows and doors (weather permitting)
• Set up fans to create cross-ventilation — aim them outward through windows to push humid air outside
• Run dehumidifiers — ideally commercial-grade units. Domestic dehumidifiers help but have limited capacity for flood-scale moisture
• Do not use your HVAC system if it was affected by flooding. Contaminated ductwork will spread mould spores throughout the house

The next 24 hours: drying and assessing

Remove compromised materials

Certain materials cannot be effectively dried and should be removed:

• Carpet and underlay — if soaked with floodwater (Category 2 or 3 water), it should be discarded. Clean water spills on carpet can sometimes be saved if dried within 24 hours
• Plasterboard — if the waterline is visible, cut the plasterboard at least 30cm above the waterline and remove it. Plasterboard wicks moisture upward, so the wet zone extends higher than the visible line
• Insulation — wet insulation (especially batts) loses its effectiveness and becomes a mould incubator. Remove and replace it
• MDF and particleboard — these swell irreversibly when wet and should be replaced

What you can usually save

• Solid timber — if dried quickly, solid timber furniture and structural framing usually recovers well
• Metal items — wash, dry, and treat for rust
• Hard plastic and glass — wash with detergent and dry
• Clothing — machine wash in hot water with detergent. Items that cannot be washed should be dry-cleaned or discarded

Monitor with a moisture meter

If you have access to a moisture meter (available from hardware stores for around $30–$60), check walls and floors daily. Building materials should reach a moisture content of 15% or below before being closed up or replaced. Anything above 16% is at risk of mould growth.

When to call a professional

Call a professional mould remediator or water damage restoration company if:

• The flooded area exceeds 10 square metres
• The water was contaminated (stormwater, sewage, river water)
• Water has been present for more than 48 hours
• You can smell mould or see visible growth
• The property has wall cavities, subfloors, or concealed spaces that were affected
• Anyone in the household has health conditions that make mould exposure particularly risky

Professional restoration companies have industrial dehumidifiers, air movers, HEPA air scrubbers, and moisture detection equipment that dramatically accelerate the drying process and prevent mould establishment. For large-scale flood recovery, commercial fogging can treat entire properties quickly and effectively.

Insurance considerations

Most home and contents insurance policies cover sudden water damage (such as burst pipes or storm flooding), but coverage varies. Key points:

• Document everything — photographs, videos, and written notes with dates. This is your evidence for the claim
• Report the claim immediately — most insurers require prompt notification. Delays can jeopardise your claim
• Keep damaged items until the assessor has inspected them (unless they pose a health risk)
• Keep receipts for any emergency work, cleaning supplies, or temporary accommodation
• Ask about mould specifically — some policies exclude mould damage, or only cover it if you can demonstrate you took reasonable steps to prevent it (which is another reason to act fast)
• Get professional quotes — insurers generally prefer to see itemised quotes from licensed professionals

Long-term prevention after flooding

Once the immediate crisis is resolved, take steps to prevent future mould issues:

• Have the property professionally assessed — hidden moisture in wall cavities and subfloors can cause mould problems months after the event
• Improve drainage — clear gutters, extend downpipes, grade soil away from foundations
• Install or upgrade ventilation — ensure bathrooms, laundries, and subfloors have adequate airflow
• Consider a whole-home dehumidification strategy — particularly if your area is flood-prone. A maintenance program can provide ongoing protection
• Monitor humidity — keep indoor relative humidity below 60%. Inexpensive hygrometers make this easy to track

How we can help

At Pureairo, we specialise in post-flood mould assessment and remediation. Our SAN-AIR treatment system eliminates mould naturally — no harsh chemicals, no toxic residues — making it safe for families and pets to return to their home as quickly as possible.

If your property has been affected by flooding — whether in Sydney or Brisbane — the sooner you act, the better the outcome. Contact us for an assessment, and we will give you a clear picture of what needs to be done.