How to Remove Mould and Black Spots from Pavers

To remove mould from pavers, sweep the area, wet it, apply an outdoor mould and algae cleaner at the label strength, leave it for the time the label gives, scrub, then rinse at low pressure. Keep the jet out of the joints and stop the runoff reaching the drain. Some black spots are lichen rather than mould, and lichen can take more than one clean to shift.

At Aussie Duo Cleaning Service, we remove mould and black spots from paths, patios and driveways across Canberra and Queanbeyan as part of our high pressure cleaning service. This guide explains what the spots are, why they come back and how to clean them safely.

Black, green or grey spots on outdoor paving are usually one of three things:

• Mould and mildew: dark, fuzzy or slimy patches in damp, shaded spots.
• Algae: a green or black film that makes paving slippery when wet.
• Lichen: small, flat, round spots that look painted on and hold on tightly.

Lichen is worth knowing about because it behaves differently. The Australian National Botanic Gardens explains that a lichen is not a single organism. It is a partnership between a fungus and an alga or cyanobacterium. The same page notes lichens can grow on man-made surfaces such as concrete and bitumen. Because it grips the surface, lichen often needs a cleaner, time and more than one clean.

Mould, algae and lichen need moisture and shade. That's why they show up on south-facing paths, under trees, beside fences and anywhere that stays damp through Canberra's winter. Leaf litter and soil in the joints hold moisture and give them more to feed on.

You can slow regrowth by sweeping often, trimming back plants that shade the paving, and clearing leaves and soil from the joints. Shaded areas will still need cleaning more often than sunny ones.

Growth on paving isn't only a looks problem. The Queensland Government's tips to reduce falls at home point out that outdoor tiles and paths can be slippery when wet, and suggest keeping paths free of moss and leaves. Safe Work Australia lists polished, wet or greasy floors among the common causes of slips.

If an older relative visits, or your entry gets busy, cleaning shaded paths before winter and again before summer can make them safer to walk on.

Pick a dry, mild day with no rain forecast, so the product isn't washed away before it works. Then follow these steps:

If you're using a pressure washer, start on a low setting and hold the nozzle at a steady distance. Our guide on how to clean a driveway covers pressure washer technique and paver joints in more detail.

Most outdoor mould cleaners are strong chemicals. The Better Health Channel's advice on chemicals in the home warns that chemicals "may create a poisonous gas or liquid when mixed", so never combine products or add one on top of another. It also says to read the label first and wear the recommended gloves, goggles and face mask.

Safe Work Australia notes that safety data sheets hold important safety information about hazardous chemicals. If you're not sure how to use, store or dispose of a product, check its safety data sheet or ask the supplier.

Mould cleaner and dirty rinse water shouldn't go into a street drain. In Canberra, there is no treatment plant for the stormwater system, so anything that enters a drain ends up in creeks and lakes. Access Canberra's guidance for mobile carpet cleaners says it is an offence to let contaminated water enter the stormwater system, and it recommends directing wastewater to the sewer instead.

At home, that means using only the product you need, sweeping up debris before you rinse, and keeping runoff away from the gutter where you can.

Some marks stay after the first clean. Lichen holds on tightly, and old staining can sit deep in porous pavers. Scrubbing harder or turning up the pressure is the wrong fix. It's more likely to damage the paving surface and blow the sand out of the joints.

If spots are still there after a second treatment, it may be time for a professional clean. On pavers, we use a lower pressure and a rotary surface cleaner, and we pre-treat mould before cleaning. We'll tell you what to expect before we start. We don't re-sand or seal pavers after cleaning.

When we clean mouldy paths, patios and driveways, we check the paving for loose pavers and cracks first. Then we pre-treat the mould with an outdoor cleaner mixed to the label and give it time to work. We clean with pressure set to suit the surface, and plan how to manage the wash water at each site.

For more on concrete and paved driveways, see our driveway cleaning page. If the mould is on a painted or rendered wall, a soft wash is the safer option. Our guide to pressure washing vs soft washing explains the difference.

Aussie Duo is a family-owned Canberra cleaning business, working since 2013. Our pressure cleaning is $4.40 per square metre including GST, with a $187 minimum job, and we confirm the price before we start. See our pressure cleaning prices for examples.

Request a free quote or call 02 5501 3316. We usually reply within 30 minutes during business hours, Monday to Saturday, 7am–7pm.