Homeowners · 4 min read · Updated 6 November 2026
Can you soft wash pebbledash? Cleaning dashed and roughcast walls
Why pebbledash gets so dirty
Pebbledash, where small stones are thrown onto wet render, and roughcast, where the stones are mixed into the final coat, were used on huge numbers of UK homes from the 1920s to the 1970s, especially 1930s semis and council-built houses. The rough surface has thousands of tiny ledges that hold moisture, dust and spores. North-facing walls, walls under trees and areas below leaking gutters often turn green or black within a few years.
Many pebbledash walls have also been painted at some point. Painted dash behaves more like smooth painted render and can show streaks and flaking where paint has failed.
Why high pressure is a problem
A pressure washer can make pebbledash look clean in patches, but it tends to cause more problems than it solves on older dash.
- Stones can be knocked loose, leaving bald patches that are hard to match
- Water is forced into hairline cracks and behind hollow render
- Old paint can be stripped unevenly, leaving a blotchy finish
- Growth deep in the texture is moved around rather than killed
- Spray and debris coat windows, doors and neighbouring property
Soft washing works differently. A diluted biocide is applied at low pressure, left to work, then rinsed gently. The growth dies at the root, so the surface stays cleaner for longer.
What soft washing can and cannot fix
| Problem | Will soft washing help? |
|---|---|
| Green algae and black mould | Yes, this is what it is designed for |
| Orange or red staining | Usually, with the right treatment |
| Lichen spots | Often lightened, may need repeat treatment |
| Rust stains from metal fixings | Partly, may need a specialist product |
| Flaking or peeling paint | No, needs preparation and repainting |
| Hollow or cracked render | No, needs repair |
| Missing stones | No, needs patch repair |
Checking the wall first
Before cleaning, it is worth walking around the house and tapping the dash lightly with a knuckle or the handle of a screwdriver. A hollow sound usually means the render has come away from the wall behind. Look for cracks around windows, at corners and near the ground. Small areas of hollow render are common on older houses, but large ones may need repair before or after cleaning.
A good soft wash contractor will look for these issues and point them out before they start, so you know what to expect from the finished result.
How a pebbledash soft wash is done
- Plants, ponds, cars and windows below the walls are protected
- Loose debris, cobwebs and heavy moss on sills are brushed off
- The biocide is applied at low pressure, working in sections
- It is left to dwell for the time stated on the product label
- The walls are rinsed gently from the top down
- Stubborn areas are treated again rather than blasted
On textured dash the solution needs to reach right into the gaps between stones, so application is usually slower and more generous than on smooth render. Some staining fades over the following days and weeks as dead growth weathers away, so the walls often look better a month after the clean than on the day itself.
Gutters and downpipes are worth checking at the same time. A leaking joint or blocked hopper keeps a strip of dash wet and is usually the first place growth returns.
How long does a clean last?
On pebbledash, a soft wash typically keeps walls clean for several years, though shaded and north-facing elevations will regrow sooner than sunny ones. Fixing the cause of damp patches, such as blocked or leaking gutters, overhanging trees and broken downpipes, makes a big difference. Some owners have a light maintenance treatment every year or two to slow regrowth.
Should you paint pebbledash after cleaning?
Many people decide after a clean that they no longer need to paint. If you do want to paint, cleaning first is essential, because masonry paint will not bond well to algae and mould. Allow the walls to dry fully before painting and use a breathable masonry paint suited to textured render. Painting pebbledash uses a lot more paint than smooth render because of the texture, so it is worth getting the clean done first and seeing if the result is good enough.
As a guide, soft washing the walls of a typical semi-detached house usually costs £300 to £600, compared with several thousand pounds to paint the same walls once scaffolding is included.
Frequently asked questions
Will soft washing remove paint from pebbledash?
It should not if done correctly. The solution is applied at low pressure and diluted to suit the surface, so sound paint is left in place. Paint that is already flaking or poorly bonded may lift during rinsing, but that paint was failing anyway. If the paint is in poor condition, the contractor should point this out before starting.
Can pebbledash be cleaned in winter?
It can be, but it is not ideal. Biocides work best when temperatures are above freezing, and surfaces need to be dry enough for the solution to soak in. Frost after cleaning can also affect wet render. Most contractors prefer to clean pebbledash from spring to autumn, though mild, dry winter days can work for lighter jobs.
How do I know if my pebbledash is safe to clean?
Check for hollow-sounding areas, wide cracks and loose stones before cleaning. Small defects are normal and cleaning will not make them worse if low pressure is used. Large areas of loose render may come away during any work on the wall, so they should be repaired. A contractor can inspect from the ground and advise before quoting.
pebbledash roughcast render 1930s houses
