Soft Wash Roof Cleaning: How It Works and When It Suits

What goes into a soft wash

A soft wash combines water with dilute products such as algaecides, surfactants and biocides, applied through a low pressure system. The surfactant helps the mix cling to the tile instead of running straight off. The active ingredients then work into the growth, and the low pressure rinse carries away what has been loosened.

The pressure is closer to a garden hose than a jet wash. The cleaning is done by the solution and the time it is left to work, not by force.

Which roofs suit soft washing

Concrete and clay tiles with algae, lichen, black streaks or a thin layer of moss usually respond well. So do older or more fragile roofs where high pressure would risk damage. Slate can be soft washed too, with care around the edges and fixings.

Very thick cushions of moss are a different job. The solution cannot reach the tile through a deep mat, so those roofs are scraped first and soft washed afterwards. Some roofs are better suited to a low pressure wash or a hot steam clean, which is why we look at the tiles before recommending a method.

Soft wash moss removal step by step

First the surroundings are protected: plants, ponds and anything below the roof line. Heavy moss is removed by hand if needed. The solution is then applied evenly across each slope and left to dwell. A gentle rinse follows where needed, and the gutters are cleared of the debris that comes down. A treatment is finished on top to hold regrowth back, intended to last up to three years.

The roof often keeps improving for a few weeks afterwards as rain washes away growth that has been killed but not yet shed.

Soft wash compared with pressure washing a roof

High pressure water removes growth quickly but can erode the face of concrete tiles, crack brittle ones and push water where it should not go. It also leaves spores behind, so growth tends to return sooner. A soft wash avoids those risks and kills what it touches. The trade off is that it relies on chemistry and dwell time, so it must be applied by someone who understands the products.

Safety and training

Because the solution kills organic growth, it has to be mixed and applied carefully. Our team completed biocide training in 2024 and is fully insured. We avoid spraying in wind and ask for pets to be kept indoors until treated areas have dried.