Mould and Algae Removal in Cairns

Three different organisms, three different colours

What people call mould on a Cairns exterior is usually three separate things, and they do not all behave the same way.

The black spotting on eaves, soffits and under gutter lines is fungal. It feeds on the film of dust, pollen and salt that settles on a sheltered surface, and it favours those spots precisely because rain never rinses them.

The flat green film on a shaded southern or eastern wall is algae, and it needs almost nothing to live on beyond moisture and light. It is the fastest to establish after the monsoon and the fastest to come back.

The orange or rust coloured staining that shows up on Colorbond fences, retaining walls and the sunnier side of a render wall catches most people out, because it looks like rust and gets scrubbed like rust. It is Trentepohlia, a green alga carrying so much carotenoid pigment that the chlorophyll underneath is completely masked. It is a plant, it is alive, and it will not respond to a rust treatment because there is no iron in it.

Why it comes back faster up here

A wall in Cairns is wet, warm and shaded for a good part of the year. Between the monsoon through December to March, overnight humidity that keeps surfaces damp until mid morning, and daytime temperatures that never really slow biological growth down, spores land on a surface that is hospitable almost year round.

The practical effect is that a properly treated wall stays clean for around twelve to eighteen months here, where the same job in a dry southern climate might hold for four or five years. Anyone promising a permanent result is selling something. What a proper treatment buys you is a full reset and a slow, even regrowth rather than patchy dark streaks returning in a couple of months.

Killing it beats scrubbing it

The reason a supermarket mould spray on the end of a hose disappoints is contact time and reach. Growth roots into the pores of render and into the grain of timber, so anything that only removes what is on the surface leaves the anchoring structure behind, and the colony rebuilds from it.

Killing it takes a solution strong enough for the organism, held on the surface long enough to work, on a substrate that can take it. That is a low pressure soft wash, applied and left, not scrubbed. Pressure is beside the point here. A high pressure lance on render will grind the growth further into the pores while leaving lance marks you cannot remove.

What to sort out before you clean

Some mould is a symptom. If the same patch on a wall keeps returning years earlier than everything around it, look for the water source before you book a wash. Air conditioner condensate lines dripping down a wall, sprinklers overspraying onto render, a blocked downpipe, or a mango tree keeping one corner permanently shaded will all rebuild the growth as fast as we remove it.

We also do not touch interior mould. Mould inside a wall cavity or on plasterboard is a building and remediation issue, not an exterior wash, and pointing you to the right trade is more useful than taking the job.

Call 07 4028 4268, or put a photo in the quote form, and we will tell you which growth you are actually looking at.