Roof Cleaning in Cairns

What is actually growing up there

Two things take hold on a roof in Far North Queensland, and they are not the same problem. Moss sits on top of the tile, holds water like a sponge, and lifts easily enough once it is dead. Lichen does not sit on anything. It anchors into the surface with rhizines that work down into the pores of a concrete tile or into the weathered glaze on terracotta. Run a broom over a lichen colony and you take the top off and leave the grey anchoring stain behind, which is why roofs cleaned that way look patchy again within weeks.

Killing lichen is a dwell time problem, not a pressure problem. The solution has to stay wet on the growth long enough to break the colony down, and on a 33 degree afternoon with a hot tile underneath it will flash off before it has done anything at all. That is the single biggest reason roof washes fail up here. We work roofs early in the day, wet the surface first, and go back over the heavy patches rather than pretending one pass was enough.

Pressure belongs on very few roofs

A high pressure lance on a concrete tile strips the cement slurry coating off the top, and that coating is the only thing stopping the tile soaking up water. Take it off and the tile goes porous, holds moisture, and grows the next lichen colony faster than the one you just paid to remove. On terracotta the glaze goes the same way.

The second issue is water direction. Tiles are laid to shed water downhill, not sideways and not uphill, and a lance forces it under the laps and into the sarking. A fair few leaks blamed on storms in January started with a roof wash in October.

Colorbond is its own case. The steel is tough but the paint system on it is thin, and the vulnerable points are the fastener washers and the sheet laps. Colorbond gets washed at low pressure, with the flow running down the fall of the sheet, never up under a lap and never straight into a screw head.

Timing it around the wet season

The useful window is April through November, once the monsoon has finished and before the humidity climbs back up. Wash a roof in February and you are working between storm cells on a surface that will not stay dry, the solution gets diluted before it can do its job, and the regrowth clock starts the same week.

It is also work worth doing before cyclone season rather than after. A roof clear of moss sheds water properly, and gutters that are not carrying a season of dead growth actually cope with a 200 millimetre day.

When we will tell you not to bother

If the tiles are crumbling at the edges, flaking in layers, or already porous enough to darken with every shower, cleaning them is money spent on a roof that needs replacing. Same with Colorbond that has gone chalky and white across the sheets. The wash will lift the growth and the colour underneath will still be gone.

If it is sound, it comes back. Call 07 4028 4268 or send a photo through the quote form with the tile type and rough age, and you will get a straight answer on whether it is worth doing.