Freshly rendered walls look crisp and bright, but in Mid Wales it doesn’t take long for green streaks to appear under windowsills and on the shady side of the house. Within a few years whole walls can turn green, red or black. The good news is that stained render can almost always be cleaned without repainting or re-rendering, as long as it’s cleaned the right way.
Why does render go green?
Green staining on render is algae. Render, especially the textured and through-coloured kinds, holds moisture on its surface, and algae only needs damp and a little light to grow. That’s why the worst staining is usually found:
- on north-facing and shaded walls
- under windowsills, where water runs off and down the wall
- near trees, hedges and neighbouring buildings that stop walls drying out
- on walls exposed to wind-driven rain, which in Powys is most of them
What about red, orange and black staining?
- Red or orange staining is usually a type of algae called trentepohlia. It’s common on modern renders in wet areas and is often mistaken for rust.
- Black staining is usually mould, lichen or a build-up of algae and pollution.
All of these are living growth. Removing the visible layer isn’t enough: unless it’s killed at the root it grows back quickly.
Why render shouldn’t be pressure washed
It’s tempting to take a pressure washer to a green wall, but high pressure and render don’t mix. It can:
- erode the surface and strip through-coloured finishes, leaving patchy areas
- force water into cracks and behind the render
- damage the silicone water repellency of renders such as K-Rend
- blast off the visible growth while leaving the roots, so it returns within months
How softwashing works
Softwashing is the method we use for render. Instead of pressure, it relies on a specialist, biodegradable cleaning solution:
- Application. The solution is applied to the wall at low pressure, similar to a garden hose.
- Dwell time. It’s left to work, breaking down algae, mould and lichen and killing the growth at the root.
- Rinse. The wall is rinsed gently, taking the dead growth and dirt with it.
Some staining disappears during the clean, and the rest continues to fade over the following days and weeks as the treatment keeps working and the rain washes the wall.
Which renders can be softwashed?
Softwashing is suitable for all the common render types, including:
- K-Rend and other silicone-based renders
- monocouche (through-coloured) render
- traditional sand and cement render, painted or unpainted
- lime render, where a gentle approach is essential
The same method is used for cladding, fascias and soffits, and other surfaces that high pressure could damage.
How long does it last?
Because softwashing kills the growth rather than just removing it, render stays clean much longer than it would after a pressure wash. How long depends on the wall: a sunny, open elevation stays clean longer than a damp, shaded one, but several years is typical.
Cleaning render before selling or letting
Stained render makes a property look neglected in sale and rental listings, and buyers often assume it will need re-rendering. Softwashing is far cheaper and quicker than repainting or re-rendering, and the difference in photos is dramatic.
Render cleaning across Powys
Williams Jet Wash Services softwashes render for homeowners, landlords, businesses, schools and housing associations from our base near Builth Wells, covering Brecon, Llandrindod Wells, Rhayader, Newtown, Welshpool and the rest of the areas we serve. Read more about our render cleaning and softwashing services, or get a free, no-obligation quote.