Experts explain how to prevent mould and mildew taking hold, and what to do if it already has

Many parts of Australia’s east coast are enduring a record wet start to the year, with frequent deluges and storms. Thousands of homes have been flooded in Queensland and New South Wales, while many more residents are noticing the effects of the damp and humid weather.

In these conditions, mould thrives. And if not dealt with, mould growth can have adverse affects on health.

Here, experts explain how to prevent mould taking hold, and what to do if it already has.

Brad Prezant, an occupational hygienist describes mould as “a visible consequence of excessive dampness”.

Mould usually looks like a “fibrous growth” on indoor surfaces like ceilings and walls, and can range from colourless to brown, yellow, green or blue. Tiny “thread like things” form its body, and contain very small spores that float in the air and spread when disturbed.

Expect to see mould when there is an excess of moisture in the air, combined with an absence of ventilation.

“If humidity stays above 85%, moisture absorbs into building materials and dusts on surfaces,” Prezant says. That absorbed moisture allows spores to germinate, which can cause a mass of mould to spread.

Prof Dee Carter, of the University of Sydney’s school of life and environmental sciences says it is not surprising there has been an increase in mould in homes this year.

As unprecedented flooding follows a humid La Niña summer, “substrates like roofs, ceilings, and wood are becoming more saturated … And this is where mould thrives”.

Mould can lead to several respiratory health problems.

“It can cause upper respiratory infection, and exacerbate asthma, especially when people are spending up to 24 hours a day in their homes,” Prezant says.

Carter says people may experience what are referred to as “sick building symptoms”, where people get wheezy, sneezy, or suffer from headaches and irritated eyes.

“These are classic allergy and asthma-type symptoms,” she says. “That is because moulds give off volatile compounds that contaminate the air, and spores that irritate people’s airways.”

“If you take away the moisture, the mould won’t grow,” Prezant says.

He suggests controlling indoor humidity with either an air conditioner or dehumidifier. Carter says it is best to run a dehumidifier for up to two hours a day per room.

Preventing rain and humidity from getting indoors is also crucial – this means only opening windows for air circulation if the air outdoors is dry.

Prezant suggests focusing on kitchen and bathroom ventilation. This includes turning fans on when excess water accumulates in bathrooms and avoiding unnecessary moisture entering an indoor space, like emptying wet clothes from a drying rack into rooms with no ventilation.

“Houses are not designed to get wet,” he says. “So either don’t release moisture into it, or have sufficient ventilation.”

There are different cleaning methods recommended depending on where the mould originated.

If mould is growing in a spot like the bottom of a window, where glass meets wood, Prezant says “there might not be much moisture inside the wood”. In this scenario, he says mould is most likely a result of condensation on the glass plane dripping down and “you could just wipe it off”.

When cleaning surface mould like this, Carter says to avoid “most bleach products on the market”. Instead, she recommends a vinegar solution of white vinegar from a supermarket, diluted in water to a ratio of 1:5.

“Vinegar will clean mould off the surface and penetrate into the substrate to kill the mould.”

Depending on the level of contamination, and concern about experiencing allergy symptoms, Carter recommends wearing a mask and gloves while cleaning mould. “Especially if it looks like it is getting hairy, or the surface looks powdery,” she says.

Carter says to keep in mind that mould “might be disturbed as you are cleaning”. This may seed more mould growth. To avoid this, use the vinegar solution in a misting bottle, and spray the surface before touching it. Also avoid banging the surface, or doing anything disruptive that could dislodge spores and send them into the air.

If dealing with high levels of moisture related to the escape of liquid from plumbing or indoor flooding, Prezant says a different approach is needed.

If mould is growing as a result of the shower leaking, for instance, removing it involves bringing up the plaster board. “It won’t be so easily controlled until the leak is stopped,” Prezant says. Or if your ceiling is mouldy because of a leak in the roof, your ceiling plasterboard “may be soaked”.

“You may wipe it off the paint surface, but water in the plasterboard and paper behind that paint is going to keep growing,” he says.

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Carter also says certain kinds of mould are worse than others. Black moulds in particular can produce potent toxins and require professionals to remediate the property.

Experts would enter the affected building in protective gear to remove the contaminated material. If the material cannot be removed, they will “work on trying to kill that mould”.

Prezant says contractors should also be used when dealing with extensive mould. He says experts will know how to stop the spread of mould in future by containing “all the tiny spores”.

Prezant says there is not much difference between mould found on walls and mildew found on clothes.

The air is relatively still inside a wardrobe. If high-moisture air infiltrates the space, Prezant says you can expect some condensation on clothing, shoes and anything else in the wardrobe.

Each material has a different propensity to grow mould – this will determine what items affected by mildew can be salvaged.

Mildew growth is often superficial on leather footwear, for example. “It is possible the mould is growing on dust or dirt on the surface,” Prezant says. In that case, you can simply wipe it off. Alternatively, a purse made of woven fabric can absorb more moisture. “The mould may be intertwined with the textile fibres, and will be difficult to clean.”