Mould After Heavy Rain: Why Gold Coast Roofs and Driveways Need a Clean

Mould, algae and lichen need three things: moisture, warmth and something to hold on to. After heavy rain the Gold Coast supplies all three at once. The Bureau of Meteorology's long-term averages for the Gold Coast Seaway show the wettest months are January to March, with February averaging about 184 mm of rain, and mean 9am humidity sitting around 70 per cent through summer.

Warm, humid days after a downpour mean roofs, render and concrete stay damp for days, not hours. Spores that were already sitting on the surface get exactly what they need, so a light film can turn into black patches and green slime within weeks. Shaded spots dry slowest, which is why the south side of a house, paths under trees and the area around downpipes go first.

Homes near the beach, the canals and the lakes, from Palm Beach and Burleigh Heads to Robina and Mermaid Waters, tend to see it sooner because the air there stays humid for longer.

Algae and mould on concrete, pavers and pool surrounds are slippery, especially when wet. After a run of rain, a driveway or front path that looked fine in winter can become a real fall risk for kids, older family members and visitors. If you rent the property out, slippery paths are also a common complaint at inspection time.

A proper clean removes the growth rather than just the top layer of dirt, so the surface grips again. On exposed aggregate and pavers the operator adjusts the pressure so the stones and joints aren't damaged.

Black streaks on a roof are usually algae. They are mostly cosmetic at first, but they hold moisture against the roof and darken it so it absorbs more heat. Lichen is the grey-green crusty growth, and it is harder on a roof: it roots into the surface of concrete and terracotta tiles and holds water against them, which over time roughens the tile surface and lets more growth take hold.

On metal roofs, constant damp under dirt and growth is not good for the paint finish or the fixings, especially near the coast where salt is in the mix. Cleaning removes the growth and lets the roof dry properly again. Because the operator has a roofing background, anything spotted that needs repairing, such as cracked tiles, loose ridge capping or rust, goes into a written roof condition report with photos.

Give it a day or two of dry weather if you can. Roofs need to be dry enough to walk on safely, and cleaning solutions work better on a surface that isn't still running with water. There is no need to wait for the whole wet season to finish, but booking straight after a long wet spell, rather than months later, stops the growth from getting a deeper hold.

If more heavy rain is forecast within a day, the operator will usually suggest moving the job a few days so the cleaning solution isn't washed off before it has worked.

It depends on the surface. Roofs, render, painted walls and weatherboards are soft washed: a cleaning solution kills the mould and lichen at the root, then it is rinsed at low pressure so tiles, pointing and paint aren't blasted. High pressure on a Colorbond roof can strip the paint finish, and on old tiles it can damage the surface.

Concrete driveways, paths and pool surrounds are pressure cleaned with a surface cleaner, at the right pressure for the material. Exposed aggregate and pavers need a lighter touch than plain concrete. Solar panels are only cleaned gently with fresh water and a soft brush. Asbestos cement roofs and walls are never pressure cleaned.

Wash water is kept out of the street and stormwater drains. In Queensland, letting pressure cleaning wash water into roadside gutters or stormwater is against the law.

On this site's published prices, roof cleaning starts from $950 for an average single-storey home, house washing from $550 (single storey) or $850 (double storey), and driveways, paths and pool surrounds from $290, with a $250 minimum job. Gutters start from $290 and are included with a roof clean. Every price is confirmed with you before work starts.

Combining the roof, house and driveway in one visit after a wet spell is usually the best value, because the setup is only done once. See the roof cleaning and driveway cleaning pages for what each includes, or get a free quote and one local, insured operator will reply, usually within one business day.