Short answer
Pressure washing uses a powerful jet of water to blast dirt off hard surfaces such as block paving and concrete. Soft washing uses low pressure and a cleaning solution that kills algae and staining at the root, which is then rinsed gently away. Soft washing suits surfaces that a strong jet could damage, such as render, painted walls and many timber surfaces.
What is pressure washing?
Pressure washing, often called jet washing, relies on force. A machine pushes water through a narrow nozzle at high pressure, and the impact of the water lifts dirt, moss and grime from the surface. On tough, dense materials it is quick and effective, and with a rotary surface cleaner attachment it gives an even finish across a large area.
The same force is its weakness. On softer or coated surfaces, a high-pressure jet can scour the face of the material, strip paint, force water into cracks and wash out the sand or mortar in joints. It can also remove visible growth without killing the spores underneath, so green algae may return sooner than expected.
What is soft washing?
Soft washing relies on chemistry rather than force. A cleaning solution, usually including a biocide, is applied to the surface at low pressure. The solution is left to work so that it breaks down the dirt and kills the algae, lichen and mould growing on the surface. The wall or surface is then rinsed gently, without a damaging blast of water.
Because the treatment kills spores rather than just rinsing the top layer, the surface tends to stay cleaner for longer than after a rinse alone, and faint marks can carry on fading after the work is finished. The right products, dilution and protection for windows, plants and neighbouring surfaces all matter, which is why soft washing is usually a professional job on anything larger than a small area.
What is biocide, and what does dwell time mean?
A biocide is a treatment that kills living growth such as algae, lichen and mould. In cleaning, dwell time simply means the period the solution is left on the surface before it is rinsed off. That period depends on the product, the type and depth of growth and the weather, and it should always follow the product instructions. Rinsing too soon wastes the treatment; letting it dry on in hot sun can leave marks.
Some biocides keep working after the visit, which is why staining sometimes continues to lighten over the following period rather than vanishing the moment the wall is rinsed.
Which surfaces suit which method?
Surfaces that usually suit pressure washing, used with care, include block paving, concrete, tarmac and many hard paving slabs. Even here, technique matters: block paving loses joint sand, and natural stone such as sandstone needs a lower setting. Our patio and driveway guides cover those surfaces in detail.
Surfaces that usually suit soft washing include render of all kinds, painted masonry, brick and stone walls where the mortar needs protecting, and many timber surfaces. These are the places where a high-pressure jet risks damage that is far harder to fix than the original dirt.
Many homes have both kinds of surface side by side, so it is common for a single visit to use pressure washing on the drive and soft washing on the walls.
Choosing a method, step by step
- Identify the material: render, brick, stone, timber, concrete, block paving or something else.
- Check its condition. Cracks, flaking paint, loose mortar or soft timber all point away from high pressure.
- Look at the staining. Green and black growth responds best to a treatment that kills it, not just a rinse.
- Check any manufacturer or installer guidance, particularly for render systems, coatings and engineered surfaces.
- Test your chosen method on a small, hidden area and wait for it to dry before going further.
When to call a professional
Soft washing walls involves working at height, handling cleaning solutions and protecting glazing, plants and neighbouring property, so it is worth calling a professional for anything beyond a small, ground-level area. The same applies if you are not sure what your wall is made of, or if earlier cleaning has left it patchy.
We soft wash render, brickwork and stone using low pressure and a specialist solution that kills algae at the root, and we avoid pressure washing render because it can damage it. Our guide to cleaning render goes into more detail on render itself.
Rather have it done for you?
Soft washing of render, brick and stone to remove algae and black streaks. Family-run by Jason and Lucas Prior, covering south Essex.
Frequently asked questions
Is soft washing better than pressure washing?
Neither is better everywhere. Soft washing is gentler and better suited to render, painted and timber surfaces; pressure washing is effective on hard surfaces such as block paving and concrete when used carefully.
Does soft washing use chemicals?
Yes. Soft washing relies on a cleaning solution, usually including a biocide, applied at low pressure and rinsed off gently. Choosing and diluting it correctly is part of doing the job safely.
Can soft washing be used on block paving?
A biocide treatment can be useful on paving where green growth keeps returning, but the dirt itself is usually lifted with a pressure washer or rotary surface cleaner, used carefully to protect the joints.
Related guides
- How to clean render: safe ways to clean green and black staining from rendered walls, and why a jet wash is usually the wrong tool.