Render Cleaning & Softwashing: Why K-Rend and Coloured Render Go Green

Coloured silicone render — K-Rend, Weber, Sto and similar systems — has transformed the look of homes across Dorset, Somerset, Wiltshire and Hampshire. Freshly applied, it's crisp, clean and vibrant. But within a few years, many rendered walls develop a familiar problem: green, pink and black staining that creeps across the surface, particularly on north-facing and sheltered elevations.

The cause is almost always organic growth — algae, mould and lichen — and the solution is softwashing, not pressure washing.

Why render goes green

Render provides a slightly porous surface that holds a thin film of moisture. On elevations that get less direct sunlight — north-facing walls, sheltered gables, walls under overhanging trees — that moisture lingers long enough for airborne algae spores to take hold.

Once established, the growth feeds on the moisture and mineral content in the render, spreading across the surface as a green or pink biofilm. Black staining is usually a sign of mould or lichen. None of it damages the render itself immediately, but it's unsightly, and over time it can become ingrained.

Why pressure washing makes it worse

Pressure washing feels like the obvious fix, but on coloured render it's the wrong choice:

• It erodes the surface. Silicone render has a thin coloured topcoat. High-pressure washing can strip that coating, leaving patchy, faded areas that can't be restored without re-rendering.
• It doesn't kill the growth. Blasting away the visible green leaves the root system of the algae in the render. Within months, the staining returns — often worse.
• It can drive water behind the render. Forcing water at high pressure risks getting it behind the render system, where it can cause damp and blistering.

How softwashing restores render

Softwashing uses a low-pressure, biocidal solution to kill the organic growth at the root rather than blasting it away. The process is gentle on the render but thorough on the growth:

1. Assessment. We identify the render system and the type of staining to choose the right biocidal solution and strength.
2. Application. The biocidal softwash is applied at low pressure, where it penetrates the surface and kills algae, mould and lichen at the root.
3. Dwell time. The solution is left to work, breaking down the biofilm and staining.
4. Gentle rinse. A low-pressure pure-water rinse lifts the dead growth away without damaging the render surface.

Because the root system is killed, the render stays cleaner for far longer than it would after a pressure wash — typically 2–3 years before any significant regrowth, longer with a follow-up maintenance treatment.

Which surfaces can be softwashed?

Softwashing is safe for most rendered surfaces, including:

• K-Rend and other silicone renders
• Monocouche and through-coloured renders
• Painted masonry and pebbledash
• Brickwork and stone (where staining is organic, not mineral)

For mineral staining — rust, efflorescence, paint — different specialist treatments are needed, and we'll advise on those honestly if that's what we find.

Get a free render cleaning quote

If your render is going green, the sooner it's treated the easier and cheaper it is to restore. We cover homes and businesses across Dorset, Somerset, Wiltshire and Hampshire.

Get your free render cleaning quote or call us on 01747 413013.