Soft Washing in Cairns

Soft washing is a chemistry problem

The pressure in a soft wash is roughly what comes out of a garden hose, well under 500 psi at the surface, and none of the actual cleaning is done by the water. The work is done by the solution: a surfactant that makes the mix cling to a vertical wall instead of running straight to the ground, and a measured amount of sodium hypochlorite that kills mould and algae at the root rather than knocking the visible top off it.

It is an unimpressive thing to watch. There is no stripe of clean concrete appearing behind a lance. The wall darkens slightly when the mix goes on, the growth dies off over the next several minutes, and the rinse carries it away. The result arrives all at once at the end.

Why the dilution is never one number

Two things move the mix strength: what the surface is made of, and how far the growth has gone.

Old chalky paint on a Queenslander takes a weaker solution and a longer dwell, because a strong mix on failing paint will lift it. A Colorbond fence with heavy staining takes a stronger mix and a shorter contact time. Bare timber takes no chlorine at all and gets different chemistry entirely.

Here is the part almost nobody mentions. Sodium hypochlorite loses strength sitting in the drum, and it degrades faster in a hot shed in Cairns than it would anywhere down south. A mix made to the same ratio from month old stock can be well under half the strength it was when the drum was fresh. That is why a crew working to a fixed recipe gets wildly different results across a year, and why the strength gets checked rather than counted in scoops.

What it suits, and what it does not

Soft washing is the right method on rendered block, painted fibre cement, weatherboard, eaves and soffits, tile and Colorbond roofs, metal fencing and painted timber. Anything where forcing water sideways into a join, or stripping a coating off, would cost you more than the dirt does. Roof cleaning and house washing are both soft wash jobs for that reason.

It is the wrong method on a concrete driveway. Concrete is hard, it has no laps or sheet joins to drive water behind, and the growth sits deep in the pores where a low pressure rinse will never reach. That is a genuine high pressure job, and treating it as a soft wash just means a slow, half finished slab.

The other half of the method is preparation. The solution that kills algae will also burn foliage if it dries on a leaf. Everything inside the rinse zone gets soaked before we start, covered where it needs covering, and rinsed again afterwards. Water already sitting on a wet leaf dilutes whatever lands on it, and that is the whole trick.

Where it is not worth doing

If a wall is holding moisture from a failed flashing or a cracked render join, a soft wash will clear the surface and the same dark patch will be back within a season, because the water feeding it never stopped. Fix the source first. We would rather say that on site than take the money twice.

Call 07 4028 4268 or send a photo through the quote form and describe the surface, and you will get a straight answer on method and cost.