What is black mould and how can you get rid of it?

The mould months are upon us again, but this year those dreaded black spots could pose a bigger threat than ever. Claire Coleman reports

Black mould hit the headlines recently after an inquest determined that the tragic death of two-year-old Awaab Ishak in 2020 was the “result of a severe respiratory condition caused due to prolonged exposure to mould in his home environment”.

And this winter, mould in the home could be a problem for more of us than ever, thanks to the exorbitant cost of energy.

“If people are trying to save money by not heating their homes as much as they would usually, and are drying their washing inside instead of using a tumble dryer, this can create the perfect environment for mould to form,” says Sam Bellamy of Mould Focus (mouldfocus.com), a company that specialises in mould testing, removal and prevention.

Mould is a type of fungus that has an important environmental role to play in helping to decompose organic material. Without mould, the piles of leaves that fall off the trees every autumn wouldn’t break down into nutrients that can enrich the soil – instead they’d just keep piling up.

Mould can be a range of different colours, which are influenced by the humidity, light and food source. But when people talk about “black mould” they’re normally referring to a mould known as Stachybotrys chartarum, which can grow on materials with a high cellulose content, such as wallpaper, fibreboard and plasterboard.

“Mould requires a food source and moisture to grow,” explains Bellamy. “Mould is in the air all around us but when it stumbles across a damp material, it can colonise it.” That material can be anything from plasterboard walls and carpets to silicone and wood. “You tend not to see mould growing on a tile, but if there’s a film of dust and dirt on the tile, the mould can use that as a food source.”

Even if your home is immaculate, it’s still a potential smorgasbord of food for mould, but only if it gets wet. This can happen when there’s a leak or a flood, or a collection of water – you’ll often see mould where the tile meets the shower tray as water will often sit there after a shower – but also when you get something called dew point condensation.

This is the condensation that collects on a cold window pane when you have a hot shower – and it happens when the moisture that’s in the air condenses, or changes from being water vapour to liquid water.

“Air contains moisture, but colder air can hold less water than warmer air and that’s when it condenses,” says Bellamy. “It can happen when warm air hits a cold outside wall, creating dampness that is soaked up by the wallpaper, plasterboard or skirting board, or when the air hits a cold window pane and the water drips onto the wooden frame or the window ledge.”

To avoid this, “you need to keep the home ventilated, insulated and heated,” he says. The average family can produce between 20-25 pints of water vapour per day just going about their daily business. “That vapour needs to go somewhere to avoid it being soaked up inside our homes.”

But how?

Keep the air moving

Trickle vents – narrow vents that you’ll often find on or above windows – and air bricks are vital for letting air pass through your home.

“Once, homes would ventilate naturally – you had floorboards with gaps between them, and windows designed to facilitate airflow,” says Bellamy. But now we put down carpets and install double glazing, creating hermetically-sealed environments.

Bellamy suggests ensuring that trickle vents are open and air bricks are not blocked off, and says that, even in winter, we should open windows at least once a day, and ensure internal doors are also left open to allow air to flow freely.

“You often get condensation in the corners of a room when there’s no airflow behind furniture,” he says. “Especially when furniture is pushed up against an external wall that’s at risk of dew point condensation. Keep furniture four to six inches away from walls, particularly outside walls.”

Be careful how you dry clothes

If you don’t have a tumble dryer, don’t drape damp clothes over radiators, as the moisture will evaporate into the air. The best option is to hang them in the bathroom with the extractor fan going, or a window open and the door closed.

Heat and insulate

Cavity wall insulation that stops walls getting cold, and thus stops water condensing on them, is a step in the right direction but – and this is not something you’re going to want to hear with energy prices as they are at the moment – keeping your home warm will go a long way towards preventing the formation of mould (even though the idea of having windows open and the heating on seems counterintuitive). “If you’re letting too much cold air in [which could contain a lot of moisture] you could be creating another problem,” says Bellamy. “Ideally you want to be heating any cold air as it enters the property by having your heating on at a low level throughout the day.”

Keep everything dry

“Anywhere you can see water collecting is somewhere that you can get mould forming,” says Bellamy. “So after a shower, use a squeegee to wipe down the walls and windows in the bathroom, and then dry off the bottom with a towel.” If you find condensation on the windows in your bedroom, wipe them down before ensuring that all the sills and frames are dry.

Consider getting a dehumidifier

‘By drying washing inside, this can create the perfect environment for mould to form’

“You want to keep the relative humidity at a maximum of 70 per cent,” says Bellamy, “and I advise my clients to try to keep it below 60 per cent. Just make sure that if it’s a tank dehumidifier you’re emptying it regularly.”