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Mould can menace your house, clothes and car after heavy rain, so what can you do about it?

By Jesse Thompson, Thursday February 1, 2018 - 16:56 EDT
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A Darwin local recently returned from holiday to find their pillow had grown a case of mould. - ABC

First there is rain and then there is mould.

It is a feature of Darwin's wet season as regular as heavy rain: patches of mould growing in corners, covering car seats and giving old clothes new designs.

And while the dark patches are unsightly, they can also pose a number of health risks that often fly under the radar.

In many instances the symptoms are so broad they can only be attributed to mould if they diminish when a person leaves a mould-infested environment.

"We can get very irritable; people get either depressed or aggressive, so behavioural changes," mycologist Dr Heike Neumeister-Kemp said.

"It can be irritable bowel syndrome, it can be fatigue and all kinds of headaches.

"In a nutshell, all type of fungi should be avoided because there's a possibility that they cause severe health effects."



Should I leave my house open or closed?

To help mould-proof local homes, enlisted the help of Troppo Architect co-founder Phil Harris.

When it came to the question of throwing windows and louvres open to the elements, Mr Harris laughed off the suggestion that a breezy tropical house could be insulated from the conditions outside.

"You've got to keep them open, surely," he said.

"The more open everything is, the less chance it has to build up the mould and mildew."

But some listeners begged to differ.

Ben: "I've been a cleaner in Darwin for over 20 years. Experience tells me keep things closed when you're not home and fans low or off."

Helen: "I lived in Darwin 21 years. Closed louvres and cupboard doors always worked for me in a pre-cyclone elevated home."

Dr Neumeister-Kemp said keeping a house open in the warm daytime air before closing it to the cold moist night air was an effective mould-fighting strategy.

But in Darwin, where the variations in temperature can be small and the wet season rain fairly constant, you should choose one option and stick with it.

"If you start shutting things, then you need to shut the house completely and you need to do something for humidity control," she said.

If you're leaving everything open and inviting draughts through the house, then even a high relative humidity won't yield mould.

"If you think about tropics, like Bali, where they constantly have monsoonal rain, they don't have mould because absolutely everything is open and every single door is louvred."

What about air conditioners and fans?


Fans effectively keep mould at bay by improving ventilation in a room and drying it out.



In the typically southern type of bunker-like brick housing, air conditioning can work well in conjunction with a sealed environment and well-insulated walls and ceilings.

"An energy-efficient box that's well sealed up and creates a totally internal environment is an answer," Mr Harris said.

"But it's a highly energy-efficient answer, and besides, it's bloody great fun when it's raining isn't it?"

But if the system is too cold the air conditioning can create conditions in which the mould can thrive.

"Even if it's at 24 degrees, if the outside humidity is too high and the air conditioning is not equipped to strip enough moisture out, you still can have problems," Dr Neumeister-Kemp said.

This is because of the dew point, the temperature at which water droplets condense and dew can form. It correlates directly with humidity.

Is sunshine the best disinfectant?

The question of how light might affect this equation was raised by one listener.

"Leave the light on permanently in the bathroom. Mould grows in the dark," George said.

But Dr Neumeister-Kemp disputed this, saying that both sunlight and artificial light were largely irrelevant because mould's outer cover protected it from UV light.

"It's much more important to keep the entire house out of dew point," she said.

Because the dew point is tied directly to humidity, Darwin houses with higher temperatures can form mould if the air is also filled with moisture.

Clove oil, vinegar or bleach?

If you've returned from weeks on holiday to find a wall populated with mould, what's the best antidote?



In the Goldilocks-like range of potential products, a vinegar solution is just right.

"Bleach bleaches. It takes the colour out of mould and feeds it so it's absolutely not recommended," Dr Neumeister-Kemp said.

"Clove oil works but it leaves an oily residue so mould can grow on the oil later. It's also very expensive.

"But there are many, many publications that say an 80 per cent vinegar solution works because it's an osmotic pressure that pressurises the fungus and makes it explode."

This isn't as dramatic as it sounds, but it is a cheap, environmentally friendly solution to annual wet season mould.


- ABC

© ABC 2018

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