Render soft washing

Low-pressure biocide cleaning for silicone, acrylic, monocouche, painted and pebbledash render. Removes algae and black mould safely. UK guide prices.

In short: Render soft washing is the low-pressure cleaning of rendered walls with a biocide solution that kills algae, mould and lichen, then rinses away the dead growth. It is for homeowners and landlords with green, black or orange staining on render. In the UK, a typical terraced or semi-detached house usually costs £300 to £600 and a detached house £600 to £1,100.

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Modern thin-coat renders such as silicone and acrylic are designed to shed dirt, but in damp, shaded spots they still grow algae and black mould, especially on north-facing walls and under trees. Older sand-and-cement, painted and pebbledash renders stain even more readily. The staining is living growth, not dirt, and it comes back quickly if it is simply blasted off without being killed.

High pressure is the wrong tool for render. It can scar thin-coat finishes, strip paint, dislodge pebbledash and drive water into cracks and behind the render. Soft washing applies a biocide at low pressure, gives it time to work, and rinses gently, so the surface is cleaned without damage. Some render manufacturers specify low-pressure biocide cleaning as the maintenance method for their systems.

What is included

Inspection of the render type, condition and any cracks or blown areas
Pre-wetting and protecting plants, lawns and nearby surfaces
Low-pressure application of a biocide matched to the render and the growth
Dwell time for the solution to kill algae, mould and lichen
Gentle rinsing of walls, windows, frames and sills
Cleaning of render beads, sills and plinths on the same elevations
A final walk round to check coverage and any areas still fading

Who it is for

Silicone and acrylic thin-coat render with green algae or black mould
Monocouche through-coloured render that cannot be repainted easily
Painted sand-and-cement render that is stained but still sound
Pebbledash and roughcast where high pressure could dislodge stones
Owners preparing a property for sale or re-letting
Anyone who wants to delay the cost of repainting or re-rendering

How much does it cost?

As a guide, render soft washing usually costs £300 to £600 for a terraced or semi-detached house and £600 to £1,100 for a detached house, or about £4 to £8 per m², depending on height, access and how heavy the growth is. See our full cost guide.

How it works

How render soft washing works, step by step

Identify the render

The render type and finish are identified, along with any cracks, blown patches or failing paint that need care.

Protect

Planting is soaked and covered where needed, and windows, doors and vents are closed and protected.

Apply and dwell

The biocide is applied from the bottom up at low pressure and left to work for the right length of time.

Rinse and check

Walls, glass and frames are rinsed down, plants rinsed again, and the finish checked from ground level.

Render soft washing: FAQs

Will soft washing remove all the staining from my render?

Algae and mould usually disappear during the clean or within a few days. Black lichen spots and deeper staining can take a few weeks to fade as the biocide finishes working and rain washes away the dead growth. Rust from fixings, water run-off marks, paint and efflorescence are not organic, so they need a different treatment.

Can soft washing damage silicone render?

Not when it is done with a suitable product at the right strength and low pressure. Silicone and acrylic renders are actually most at risk from high pressure, which can erode the thin top coat. Check whether your render manufacturer has care guidance, as some recommend specific cleaning products for their systems.

Should I repaint or soft wash my render?

If the render is sound and the paint is not flaking, soft washing is usually the first step, as it costs far less than repainting. If you do plan to repaint, soft washing beforehand is still worthwhile, because painting over live algae and mould leads to staining coming back through the new paint.

Why is my render going green again so quickly?

Render grows algae fastest where it stays damp: on north-facing walls, under trees, near leaking gutters and where water runs off sills. If growth has only been pressure washed off, spores left in the surface regrow quickly. Killing the growth with a biocide and fixing sources of damp both help a clean last longer.