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Brick Cleaning Specialists — brick cleaning and pressure washing, Warilla NSW

Kill it at the root

Mould, Algae & Lichen Removal

Black streaking on a rendered wall, green film on a shaded path, grey-white crusting on roof tiles. All three are living organisms with a root structure, which is why blasting them off buys you about one season.

Looks like

Black, green, grey-white patches

Found on

Render, paint, brick, roof tiles, timber, concrete

Our verdict

Very treatable — kill it, do not blast it

Quick answer

How do you permanently remove mould from exterior walls?

Exterior mould, algae and lichen are removed by applying a biocidal solution at low pressure that kills the organism through its full depth, then rinsing gently — not by high-pressure blasting, which removes only the visible growth and leaves the root structure intact. Treated surfaces typically stay clean for two to four years, against six to twelve months for a pressure blast, because there is nothing left alive to regrow from.

At a glance

Method
Biocide + low pressure (soft wash)
Treated result lasts
2–4 years typically
Blasted result lasts
6–12 months typically
Worst areas
South walls, shaded paths, treed blocks
01

Three different organisms

  • Algae — the green film on paths, fences and shaded walls. Fastest growing, easiest to kill, first to return if only rinsed off.
  • Mould and mildew — the black speckling and streaking on render, paint and eaves. Feeds on surface residue and thrives in humidity.
  • Lichen — the grey-white or orange crusty growth on roofs, fences and masonry. A symbiosis of fungus and algae, extremely tenacious, and physically bonded to the surface. Scraping it takes the surface with it; killing it lets it release on its own.
02

Why the coast is worse

Everything from Helensburgh to Ulladulla sits in high humidity with regular salt deposition, and salt is hygroscopic — it pulls moisture out of the air and holds it against the surface. That is a permanent damp film for growth to live in, which is why coastal homes go green far faster than inland ones and why the Southern Highlands, cooler and damper again, has its own heavy lichen problem.

03

Keeping it away

Treatment does most of the work. Beyond that: cut back overhanging vegetation to get airflow and light onto the wall, keep gutters and downpipes clear so water is not running down elevations, redirect irrigation off the building, and put the worst-affected elevations on a treatment cycle rather than waiting until they are black again.

Do not guess this one

Not sure if it’s mould, algae & lichen?

Several of these stains look similar and want completely opposite chemistry. Using acid on the wrong one turns a removable stain into a permanent one. Send a couple of clear photos in daylight — one close, one of the whole wall — and we will tell you what you are looking at.

Text photosCallor use the quote form

FAQ

Mould & Lichen — questions we get asked

Is exterior mould a health risk?

Outdoor growth on a wall is primarily a maintenance and appearance issue rather than an indoor air quality one. It matters more where it is on a surface people touch or walk on, because wet biofilm on a path or ramp is genuinely slippery.

Will bleach from the hardware store do the same job?

Household bleach kills surface growth but is not formulated to wet out and penetrate a colony, and without a surfactant it runs straight off a vertical surface. It also strips colour from anything it drips onto. Professional solutions are dwell-stable, cling to the surface and are rinsed and diluted properly.

How often should a coastal house be washed?

Every one to two years for most homes within a few kilometres of the water. Heavily shaded or treed properties are closer to annual on the affected elevations.

Identify it

The other eight stains

Efflorescence

White, powdery, fluffy

Calcium & Lime

White, hard, crusty or glassy

Vanadium

Yellow, yellow-green, olive

Manganese

Brown, grey-brown, tan streaking

Acid Burn

Bleached, yellowed, patchy, exposed aggregate

Rust

Orange, red-brown, running streaks

Iron Staining

Orange-brown, diffuse, blotchy

Fire & Smoke Damage

Black soot, brown scorching, tar film

Keep reading

Related work

Soft Washing

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Roof Cleaning

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Fence Cleaning

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All Hard Surfaces

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Next step

Mould & Lichen — get it looked at properly

Twenty years of masonry stain work across Sydney and the South Coast. If it can be removed, we will tell you how. If it cannot, we will tell you that too.

0448 882 780Free quote