Why the 72-Hour Window Matters

The single most important piece of practical knowledge about post-storm mould is this: the first 72 hours after a flooding or storm-water event determines whether you develop a mould problem.

If building materials that have been wetted by a storm or flood event can be dried to normal moisture content within 72 hours, mould establishment is minimal. Beyond 72 hours of sustained wetness in building materials, mould spores begin to germinate and establish colonies. By one to two weeks, colonies are firmly established and the situation has moved from prevention to remediation.

This is why professional emergency response — structural drying with industrial-grade equipment — is genuinely valuable in the immediate aftermath of a significant Northern Rivers storm or flood event. Not as a luxury, but as a way to prevent a far more expensive problem.

Northern Rivers Storm and Flood Context

The Northern Rivers region experiences significant storm and flood events with regularity. The river systems — the Richmond, Wilson, Brunswick, Tweed, and their tributaries — all have catchments that generate rapid rises when the hinterland receives intense subtropical rainfall.

The Major Recent Events

February 2022 Lismore Floods. The catastrophic February 2022 event — 14.4 metre peak on the Wilson River — is covered in detail in our dedicated Lismore flood mould guide. More than 10,000 homes inundated with Category 3 contaminated floodwater. The 72-hour window was missed for most properties.

March 2022 Secondary Floods. Lismore and surrounding areas flooded again within weeks of the initial February event — on properties still in the initial stages of recovery. This compounding event significantly complicated remediation efforts.

Cyclone Alfred — February/March 2025. Tropical Cyclone Alfred’s impact on the Northern Rivers and Southeast Queensland in early 2025 caused significant storm damage and flooding across the Tweed Valley, Murwillumbah, and Northern Rivers. Wind damage caused building envelope failures that allowed water ingress; associated flooding from the Tweed and other river systems inundated low-lying properties. The combination of roof damage and flood inundation created complex, multi-source water damage in many affected properties.

Regular annual flood events. The Northern Rivers doesn’t require a named cyclone to cause significant flooding. Regular wet-season rain events cause localised flooding throughout the region annually — in the lower reaches of the Brunswick Valley, along Bangalow Creek, in Mullumbimby lowland areas, and in the Richmond Valley between Lismore and Casino.

What Happens After a Storm or Flood: The Mould Timeline

Hours 0–72: The Prevention Window

In the first 72 hours after a water event:

Visible water must be removed immediately using pumps, wet-vacs, and absorbent materials
Building materials must begin drying — industrial air movers (not standard fans) and dehumidifiers create the airflow and dehumidification needed for rapid structural drying
Damaged building envelope must be temporarily secured — tarped roofs, boarded windows, secured doors
Category 3 water (floodwater) contact surfaces must be sanitised before drying continues
Soft furnishings and porous materials that cannot be dried (carpet, foam mattresses, saturated insulation) must be removed and replaced — these cannot be dried fast enough within the window

If you achieve adequate drying within 72 hours, you dramatically reduce (though don’t eliminate) the risk of significant mould establishment.

Days 3–7: Early Mould Establishment

By days three to seven, mould spores that were not removed during initial clean-up have begun germinating on wetted surfaces. At this stage, visible mould is not yet apparent in most cases, but mould growth is underway. Professional antimicrobial treatment at this stage can significantly reduce the colony development.

Building materials that are still elevated in moisture by day three should be considered at high risk — structural drying should be continued aggressively, and professional assessment is warranted.

Weeks 2–4: Visible Mould

Visible mould typically begins appearing on surfaces two to four weeks after a significant water event, depending on the severity of wetting and the ambient conditions. In the Northern Rivers wet season, with ambient humidity above 80%, visible mould development can be faster.

Surface mould visible at this stage is only the surface expression — colonies have established below the surface and in concealed spaces.

Months and Years: The Concealed Mould Legacy

As documented in the Lismore 2022 experience, mould that has established inside wall cavities, in insulation, and in subfloor spaces can remain active indefinitely in the Northern Rivers climate. Properties that were not professionally assessed and remediated in the initial weeks after a flood event often have chronic concealed mould years later.

What to Do Immediately After Storm or Flood Damage

Safety First

Do not re-enter a flood-affected property until:

The building has been structurally assessed and is safe to enter
Electricity is confirmed OFF to all circuits (water and electricity are lethal)
You are wearing appropriate PPE (rubber boots, nitrile gloves, N95 respirator if there is any visible mould or flood odour)

Document Before You Clean

Before removing anything or cleaning up, take photographs of:

Water levels (marked on walls, visible tidelines)
Affected rooms and materials
Any visible mould
Structural damage

This documentation is essential for insurance claims.

Remove Water and Begin Drying

The priority is getting water out and air moving. This means:

Pump out or mop up standing water
Remove saturated materials that cannot be dried (carpets, foam, saturated insulation)
Open windows and doors to create airflow (do this in dry weather only — opening up in continued rain or high humidity achieves little)
Position fans to move air across wet surfaces
Hire or arrange industrial dehumidification if available

Do not close the property up. A closed, humid post-flood building is ideal for mould.

Contact Your Insurer

Report the damage to your insurer immediately. Do not undertake any non-emergency remediation work until you have an insurer case reference and understand the claim process. Some insurance companies have preferred suppliers for flood damage remediation — using your own contractor without approval can complicate claims.

Arrange Professional Assessment

Within the first week post-event, arrange a professional assessment of the property’s moisture condition. This provides documentation for the insurance claim, identifies materials that require removal or professional drying, and establishes a baseline for post-remediation clearance testing.

Cyclone Alfred 2025: Specific Murwillumbah and Tweed Valley Context

Cyclone Alfred’s impacts on the Tweed Valley and Murwillumbah in early 2025 included:

Cyclonic wind damage causing building envelope failures (damaged roofs, broken windows) allowing significant water ingress even in properties not reached by floodwater
River flooding from the Tweed and associated waterways inundating low-lying properties
Extended rainfall periods maintaining elevated soil moisture for weeks after the event

For Alfred-affected properties in Murwillumbah, Uki, Stokers Siding, and surrounding areas:

Roof damage that allowed sustained water ingress through the ceiling may have saturated roof void insulation and ceiling materials — a concealed mould risk that isn’t visible from below
Properties that experienced both wind damage water ingress and flood inundation have compound moisture sources that require comprehensive assessment
The Tweed Valley’s high rainfall environment means that elevated moisture in building materials persists longer than in drier climates

Frequently Asked Questions

My house got wet in a storm but I dried it out quickly. Do I still need a professional assessment? If the wetting was limited and you can confirm materials dried within 72 hours, significant mould establishment is unlikely. However, if any structural materials (wall cavities, insulation, subfloor spaces) were wet and you cannot confirm they are now at normal moisture content, a professional moisture assessment is warranted. Some materials look dry on the surface while remaining elevated in the substrate.

How do I know if my property was affected by Category 3 (contaminated) floodwater vs clean storm water? Category 3 water comes from river or stormwater flooding that has mixed with sewage systems, agricultural runoff, or industrial contamination. Clean storm water from rainfall through a sound roof is typically Category 1 (clean) unless it has collected contamination from the roof surface, gutters, or soil. If your property was inundated by rising river water or floodwater that came from outside rather than through the roof, treat it as Category 3. If you’re unsure, treat it as Category 3 to be safe.

Can I claim storm mould remediation on my home insurance? Coverage depends on your specific policy. Most home and contents policies cover storm damage, and mould that is a direct consequence of storm damage may be included in a storm claim. Mould as a standalone condition (without an associated storm event) is typically not covered. Contact your insurer, document everything, and we can provide the documentation needed to support your claim.

I missed the 72-hour window — is it too late to do something useful? No. The 72-hour window is the optimal period to prevent mould establishment. After that window, the objective shifts from prevention to remediation — but remediation is still possible and effective at any stage. The longer the delay, the more established the mould and the greater the remediation scope — but there is no point at which effective remediation becomes impossible.

Get Post-Storm Mould Help

Request a Free Quote — we prioritise post-storm and post-flood assessments and can typically schedule within 24 hours for Northern Rivers properties. For active emergency situations, call us directly.

Mould After Storms in Northern Rivers: The 72-Hour Window