Pressure washing on its own removes the look of mould and mildew, but not the mould itself. The spores stay behind, and it grows back quickly. To get rid of it properly, you need the right treatment.
I'm Troy Hillard, founder and franchisor of Wash Rite. I've been in exterior cleaning since 2015, and the Wash Rite group now runs 142 trucks across Australia and New Zealand. Here's what actually works on mould, moss and lichen, and why getting rid of it quickly matters.
Where mould grows on Australian homes
On the average Australian home, most mould, mildew, moss, lichen and algae grow in a few places:
- The roof.
- The shaded south-western side of the house.
- Sandstone block retaining walls, common across New South Wales, which are a magnet for moss, mould and algae.
Why pressure alone isn't enough
Blasting mould with water removes what you can see, but the spores survive and the growth comes back quickly.
To kill it, you need a soap containing sodium hypochlorite, which is chlorine. That's what kills moss, mould and algae spores. Use anything else and you'll see rapid regrowth of what you've just cleaned off.
Some people hear "chlorine" and think harsh chemical. But it's the same chemical water authorities add to keep your drinking water safe. Used at the right dose rate, as we do, it's safe.
Why it matters: mould eats away at your home
Mould, moss and lichen aren't just unsightly. They break down your paint, your roofing and your concrete tiles.
Paint and roofing are there to keep your house weathertight. Once that outer protection breaks down, your weatherboards start to rot or your roof starts to leak, and from there your whole house deteriorates rapidly.
Two ways to clean a mouldy roof
For moss, mould and lichen on your roof, Wash Rite offers two options.
1. A moss and mould roof treatment. We spray your roof with a treatment designed to stay on it. It kills the moss, mould, algae and lichen, usually within two or three hours. Over the next three to five months, wind and weather wash away the dead growth, and your roof comes clean. It's by far the cheaper option, typically $250 to $350 plus GST, and it's the one we recommend most.
2. A full roof wash. Our team harnesses up and cleans your roof by hand, leaving it spotless by the end of the day. That may sound better, but a roof wash usually costs two to three times as much as a treatment.
Case study: the roof that saved a sale
We recently worked on a house for sale on the New South Wales South Coast, not far from Nowra. Its roof was heavily covered in lichen, moss and mould.
The house had an offer, but it was conditional on two things: the roof had to be cleaned, and the clean couldn't cause any damage. The seller called Wash Rite. We inspected, quoted and completed a full roof wash.
Two days later, a building inspector carried out a pre-purchase inspection. The roof came back with a perfect report. It looked amazing, and just as importantly, it had been cleaned without any damage. The offer went unconditional, and the house sold for its asking price.
Common DIY mistakes
The biggest mistakes we see from homeowners treating mould themselves come down to the chemicals:
- Using the wrong product.
- Not knowing the right dose.
- Leaving it on too long, or not rinsing it off. Bleach and chlorine are corrosive. You can use them, but they must be neutralised and rinsed off within a certain time. Otherwise they start to corrode your roofing nails, cladding nails and other fittings on your home.
A free tip for green paths
If your path or driveway turns green over winter, here's a trick that costs nothing. Next time you use bleach in the laundry, tip the leftover bleachy water over your paths. It still contains plenty of sodium hypochlorite, which helps keep them free of moss and mould through the colder months.
Just keep it off your lawn and garden beds, and away from stormwater drains.
How long results last, and how often to clean
After a professional Wash Rite clean, you shouldn't see mould growing back for at least 18 months. Your surroundings make a big difference, though:
- Shaded, damp or humid spots encourage rapid regrowth.
- Sunny or drier locations, such as parts of rural central New South Wales, central Queensland and central Victoria, see slower regrowth because there's less moisture.
Here's what we recommend:
- Roof moss and mould treatment: every two years. At $250 to $350 plus GST, it's a great investment in your roof.
- House wash: every 18 months.
- House wash on the coast: no longer than every 12 months, because of the sea salt.
The one thing to remember
If you can see moss, mould or lichen on your home, it's eating away at your house every second it's there. It's breaking down the protection of your paint, your roof and your mortar. The sooner you get rid of it, the longer your home will last.
Spotted mould on your roof or walls? Contact your local Wash Rite for a free quote.
