How to prevent mould after flood or heavy rain

Mould can be a serious problem for anyone experiencing flooding or heavy rain. Here are two industry experts' advice to prevent mould from growing in your home.

Preventing mould after heavy rain or flooding

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The recent wet weather in parts of Victoria and NSW, combined with humidity and high temperatures, has created a breeding ground for mould and mildew. In this article, we discuss how to prevent mould caused by flood or heavy rainfall in your home.

A flood can be one of the most damaging and devastating things to happen to homes, businesses and industries. Aside from the immediate aftereffects caused by water flooding, the aftermath of the water that remains in homes will inadvertently lead to massive mould problems affecting the building.

Mould is hazardous not just to the property but also to the health of the home’s inhabitants. Mould can trigger asthma-like symptoms including coughing, wheezing and shortness of breath. Some common but lesser-known symptoms of mould exposure may also include sleep deprivation, muscle aches, and lethargy.

Excess moisture can be removed through a number of different ways such as improved ventilation and the employment of dehumidifiers, heaters, and other appliances.

You can take steps to avoid mould and keep yourself and your belongings safe from its damaging effects. Follow the advice below from mould and asthma experts on how to prevent mould after a flood or heavy rainfall:

Treat the cause of rising dampness immediately

Pump out all the water from your property immediately and treat the cause of rising dampness as soon as it is detected. Seal any leaks in bathrooms and roofs, overflowing gutters, and blocked vents as soon as you can. Ensure you have adequate ventilation indoors to reduce moisture before proceeding.

“Reducing the amount of moisture in a house is the best way to control mould growth. After wet weather conditions, do a thorough clean and open all the doors and windows to dry out the area as quickly as possible,” Adam Trumble, Manager of the National Asthma Council’s (NACA) Sensitive Choice® Program, said in a media release addressing the mould health hazard in Australia.

“If you can, use fans or dehumidifiers to speed up the process,” Mr Trumble added.

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Remove affected items immediately and quickly

It is important to remove all items affected by the flood as soon as possible. This is because mould can start to grow within 24 to 48 hours of flooding. That is the expert advice from Dr Cameron L Jones, a PhD level microbiologist with extensive experience in mould assessment and indoor air quality.

“Wet building materials create the perfect conditions for bacterial, yeast and fungal growth,” Dr Jones wrote in his article about the effects of flood on health.

Plasterboard and flooring will need to be completely stripped out or demolished if heavily affected by flood. Similarly, wet furnishings and possessions that are unsalvageable must be discarded as well. Doing so is essential as these can harbour mould and bacteria that can be harmful to health.

Similarly, the NACA’s mould prevention checklist recommends we “ ruthless with the cleanout, if possible – hidden damp can cause ongoing problems.”

Clean up as soon as possible

After discarding any items affected by the flood, Dr Jones recommends cleaning up the remaining affected areas with soap and water. Afterwards, use a HEPA vacuum to suck up residual mould and spores throughout the premises.

When removing the mould, ensure the room has adequate ventilation such as air circulators or open windows and doors. Wear protective equipment to protect the lungs and skin and reduce your exposure to its spores. These may include P2/P3 particulate masks, gloves, goggles, and disposable coveralls.

Remove any visible mould by cleaning with a diluted solution of bleach or naturally fermented white vinegar solution. Choice, Australia’s leading consumer advocacy group, recommends slowing down the spread of mould by cleaning the surface area thoroughly with a lot of scrubbing. Use a microfiber cloth dipped in a 4:1 concentration of vinegar and water. If using bleach, Choice suggests a bleach concentration of at least 10% to do the job. 

Dr Jones emphasises the importance of completing remedial works as soon as possible. A study conducted after the 2008 Cedar River flooding looked at bacteria and endotoxin levels in flooded homes. They found microbe levels to be 1.5 to 5.1 times higher in homes undergoing restoration than in those where restoration was complete.

Thoroughly dry your property with dehumidifiers, fans and heaters

“Even after the floodwater has gone, chronic dampness in the walls can still facilitate mould growth,” Dr Jones said.

Therefore, the property still needs to be thoroughly dried to prevent further mould growth.

“This is done using any combination of the central heating system, fans, heaters and dehumidifiers usually in combination with industrial-grade HEPA air scrubbers,” Dr Jones added.

“Home heating will reduce relative humidity, as will dehumidifiers and good ventilation,” NACA’s Mr Trumble said.

Severely flooded homes may take up to months to completely dry out. However, with the right steps, you can ensure that your home is as free from mould as possible.

Prevent mould permanently

Dampness and subsequent mould growth can return if you don't take immediate action to keep your house in good shape.

As we’ve discussed before in how to kill mould permanently, and 'How Dehumidifiers Get Rid of Mould' the most crucial factor for mould growth is moisture. That’s why it is extremely important that you remove dampness from your home at all times.

Mould can grow when indoor air has an RH level of 70% and above for extended periods of time. A relative humidity (RH) level of 60% indoors and below is recommended for mould prevention. At this level, there will not be enough moisture in the air for mould to grow.

How to get rid of mould permanently after the clean-up:

  • Kill mould immediately on sight
  • Treat all leak problems immediately
  • Ensure downspouts and gutters are clean
  • Vent clothes dryers, bathroom exhaust fans and kitchen exhaust fans outdoors
  • Ensure proper ventilation indoors (open doors and windows when possible)
  • Remove indoor pot plants (which promote mould growth)
  • Avoid the use of organic mulches and compost heaps

If you are concerned, you can purchase a hygrometer to monitor the humidity levels in your home continuously. If you're experiencing ongoing complications from persistently high humidity, a dehumidifier is your best bet for removing dampness from the air. For convenience, they can continually monitor indoor humidity levels and continue operating automatically to reduce indoor humidity levels. Additionally, they can be set to reduce indoor humidity to set levels of 60%RH and below. 

A dehumidifier is helpful in homes with severe humidity issues, or in older, less-ventilated buildings. They’re also commonly used in basements since underground areas rarely get good ventilation. Dehumidifiers are also helpful in bathrooms without windows, or in specific areas of the home that require excess moisture removal.

Mould can be a serious problem for anyone who has experienced flooding or heavy rain. Taking the necessary precautions to prevent mould from growing in your home is essential to keep your family safe and healthy. 

Be sure to immediately dry out wet areas, remove standing water and fix any leaky pipes that can reduce the potential for mould growth. It is also essential to keep humidity levels low using dehumidifiers or other available options, and ensure adequate airflow with fans and open windows. More importantly, regularly inspect the affected areas to help catch any mould regrowth before it gets out of control.


View these dehumidifiers to help with moisture damage. 


Disclaimer: The information provided in this article is for general reference only. Please seek advice from professionals according to your needs.

Ionmax Australia

Ionmax Australia

Founded in 2003, Ionmax Australia has received numerous awards and accolades for its innovative products and commitment to customer satisfaction. Ionmax dehumidifiers and air purifiers have been recognised for their effectiveness in reducing indoor air pollutants and improving air quality. The company is committed to researching and developing new and improved products that meet the needs and expectations of its customers, making it a trusted name in households across Australia and beyond.

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