An east coast low hitting the Illawarra region is not just a weather event, it’s the starting gun on a narrow window where your response determines whether you’re dealing with a manageable drying and inspection exercise or a full-scale mould remediation of your home.
Mould can establish in wet building materials within 24-72 hours under optimal conditions. In a warm Wollongong or Kiama summer and with the sustained humidity that follows an east coast low, the lower end of that range is realistic. The decisions you make in the first three days after water entry significantly affect the scale and cost of the eventual problem.
What Is an East Coast Low?
An east coast low (ECL) is a low pressure system that forms off the NSW coast and can produce extremely heavy rainfall, damaging winds and significant ocean swell. For the Illawarra, ECLs are the most significant natural disaster risk in terms of building damage and moisture intrusion.
Notable ECLs affecting the Illawarra, including events in 2021, 2022 and 2024, have produced 200-400 mm of rainfall in 24-48 hours, causing widespread roof damage, flooding, stormwater overflow into homes, and coastal erosion. Kiama, Shellharbour, Dapto, Corrimal and low-lying parts of Wollongong are consistently the most affected areas.
The 72-Hour Window Explained
When building materials get wet, the race against mould has started. The critical timeframe:
Hours 0-24: Wet building materials are still wet. Mould spores (always present in indoor air) begin to germinate on surfaces with adequate moisture. Cleaning and drying within this window prevents establishment.
Hours 24-48: Early mould colonies begin to establish on wet porous materials, drywall, timber, carpet, ceiling tiles. These early colonies are still relatively easy to remediate. Act in this window if possible.
Hours 48-72: Mould colonies are established. Visible growth may start appearing. Materials that have been wet for 48+ hours have a high probability of mould even if they appear to dry out, spores have established in the material.
72+ hours: Mould is established. Remediation scope is now significantly larger than it would have been with earlier intervention. Materials that have been wet for more than 72 hours without drying often need to be removed rather than treated.
The First 24 Hours: Emergency Response
Assess Safety First
Before entering a building that has had significant water entry:
- Confirm the roof structure has not been compromised (visible sagging, tilted walls)
- Check for electrical hazards, water near electrical panels, submerged power points
- If in doubt, do not enter, call SES (132 500) to assist with safety assessment
Stop Active Water Entry
The most urgent task is stopping new water from entering:
- Temporary tarps over damaged roof sections (SES can assist)
- Sandbags or inflatable barriers for stormwater entry points if flooding is ongoing
- Remove or protect items from rooms where water is entering
- Turn off electricity to affected circuits at the main board
Document Everything for Insurance
Before any cleanup, photograph and video:
- Water entry points (damaged roof section, inundated areas, broken windows)
- Water levels and coverage (show what’s wet and how far it extends)
- Damaged contents in place (before you move anything)
- Exterior damage
This documentation is essential for insurance claims. Once you start cleaning, the evidence is gone.
Begin Drying Immediately
The sooner you start drying, the smaller the mould problem:
Remove standing water: Mops, wet/dry vacuum, or call a water damage restoration company who will have extraction equipment.
Extract wet carpet: Wet carpet that cannot be immediately dried is almost certainly going to have mould underneath. Lift carpet from tack strips, extract water from the underlay, and allow to dry (or accept the underlay needs replacement). Carpet sitting on wet concrete for more than 24-48 hours typically can’t be saved.
Increase airflow: Open windows and doors (once rain has stopped), set up fans, remove furniture from wet floor areas to allow air circulation.
Run dehumidifiers: If you have one, run it. If you don’t, hire one, equipment hire companies have desiccant dehumidifiers available. This is worth doing for any significant water event.
Remove damaged materials: Wet insulation should be removed, saturated insulation has no R-value and becomes a sustained moisture reservoir. Wet plasterboard that has been submerged should be removed to allow wall cavities to dry.
Hours 24-72: Professional Assessment and Response
If the water event was significant, more than a minor ceiling drip, if floor was inundated, if water entered wall cavities, arrange a professional water damage and mould assessment within the first 48 hours.
What a professional brings:
- Moisture meters to map the true extent of water migration (often much further than visible)
- Thermal imaging to identify wet areas hidden in walls and floors
- Industrial drying equipment beyond what most homeowners have access to
- Moisture monitoring over time to confirm drying is occurring
Do not wait for the property to “look dry” before calling for an assessment. Building materials look dry on the surface far sooner than they are dry at the core. A plasterboard wall can feel dry to touch while still reading 30% moisture content in the cavity.
Water Categories and What They Mean
The water that enters your home during an ECL may fall into different categories that affect the remediation approach:
| Water Category | Source | Health Risk | Affected Materials |
|---|---|---|---|
| Category 1 (Clean) | Rain directly, burst cold water pipe | Low | Dry quickly, treat and retain |
| Category 2 (Grey) | Storm runoff, overflowing HVAC drain | Moderate | Remove porous materials if wet 24+ hours |
| Category 3 (Black) | Sewage overflow, flood water with contamination | High | Remove all porous materials, professional remediation |
ECL flooding that includes stormwater overflow from drains or waterways is frequently Category 3, contaminated with sewage and other pathogens. Category 3 water events require specialist remediation: all porous materials (drywall, insulation, carpet, hardwood floors) in the flooded zone must be removed, not dried in place.
See our detailed guide on category 3 water damage and mould.
What Not to Do
Don’t use bleach as a first response. Bleach on wet building materials does not substitute for extraction and drying. It temporarily suppresses surface mould but doesn’t address the moisture in the material or the mould already in the core of wet drywall.
Don’t close up the house. The instinct to close windows and doors after damage is understandable but wrong. If the weather is dry, maximum airflow assists drying. Closed windows trap moisture.
Don’t wait for the insurance assessor before starting emergency drying. Insurance companies understand that you need to begin emergency mitigation immediately. Most policies require you to take reasonable steps to minimise loss. Delaying drying to wait for an assessor may actually jeopardise your claim. Call your insurer immediately, describe what you’re doing, and document it.
Don’t ignore the smell. A musty or earthy smell appearing within 24-72 hours of water entry is mould. It’s not just the smell of wet materials drying. Act on it.
After the Immediate Response: Mould Remediation
Even with the best emergency response, some mould growth is likely after a significant ECL event. Once the property is dry (confirmed by moisture meter, not by appearance), a mould inspection assesses what has established and where, and a remediation plan is developed.
For properties in Wollongong’s established suburbs (Thirroul, Corrimal, Figtree), Dapto and the lake-adjacent areas, ECL events have a higher penetration rate due to the combination of older building stock and challenging drainage conditions. A post-event inspection rather than hoping for the best is always the right call.
Frequently Asked Questions
Does home insurance cover mould after an east coast low? If the ECL event is the cause, roof damage allowing rain entry, stormwater inundation, the resulting mould is typically covered as consequential damage from the insured event. Document the event carefully and call your insurer immediately. See our full insurance claim guide at mould remediation insurance claims.
My ceiling had a small leak during the ECL, do I really need a professional? For a minor, contained drip with no evidence of spreading moisture, a visual monitor over 2-3 days and prompt repair of the roof is reasonable. If the staining covers more than half a ceiling tile area, if the leak came through an insulated ceiling, or if there is any musty smell, professional assessment is warranted.
How long after the ECL event before mould is visible? Visible surface mould typically appears within 1-2 weeks under Illawarra conditions. However, mould in wall cavities, insulation and subfloor voids may not produce visible signs for months, only becoming apparent when it’s extensive. This is why a professional moisture assessment in the weeks after an event is more valuable than waiting for visible mould.
SES has done emergency tarping, does that mean my property is now safe? Emergency tarping by SES stops active water entry but doesn’t address materials already wet. It buys you time to start drying works and arrange professional assessment. The building fabric still needs to be assessed and dried, a tarp over the roof doesn’t dry the ceiling plasterboard underneath.
How long does post-ECL mould remediation typically take? Depending on the scale of water entry: a minor event (ceiling leak, one room) takes 1-3 days including drying time. A significant event (multiple rooms, wall cavities involved) takes 1-2 weeks including professional drying, remediation and clearance testing. Major flooding affecting the whole house may take 3-6 weeks from emergency response to clearance.
Had water in your Illawarra home after a recent east coast low? Don’t wait to see what develops. Contact Illawarra Mould Removal for an emergency assessment and response.