Pressure cleaning is genuinely transformative on the right surface, and completely ineffective on problems people routinely expect it to solve. Knowing the difference before you book saves disappointment, and occasionally saves a surface.
What it does very well
- Surface dirt and traffic grime on concrete, brick and other hard surfaces. This is what it is for.
- Moss and loose organic growth, at least the visible layer.
- Cobwebs, dust and general build-up on exterior walls, eaves and fences.
- Preparation before painting or sealing, where a clean, keyed surface matters.
- Mud, clay and construction residue, which comes off readily.
What it will not fix
Oil that has soaked in. Oil penetrates the pores. Pressure removes the concrete surface faster than it removes the oil, leaving a lighter, slightly eroded patch with the stain still beneath. It needs a degreaser or a poultice.
Rust staining. Iron oxide bonds chemically with the concrete. It requires a specific rust remover; pressure does nothing.
Mould, permanently. It removes what you can see and leaves what you cannot. Without a biocidal treatment it returns.
Tannin stains from leaves. Dye, not dirt. Needs the right chemistry.
Efflorescence. The white powdery bloom is mineral salts migrating out of the concrete from within. Wash it off and more arrives, because the source is inside the slab. It needs the moisture path addressed.
Discolouration from age or wear. Concrete that has weathered unevenly, or where the surface has worn through in traffic areas, is a resurfacing question.
Structural problems. Cracks, spalling and lifting are not cleaning issues, and cleaning can make them more visible rather than less.
Where it does harm
- Roof tiles — cracked tiles, water forced under the laps, stripped ridge capping.
- Painted timber — lifts paint and drives water behind boards.
- Render — etches and leaves visible lap marks.
- Soft natural stone — erodes sandstone and limestone permanently.
- Paver joints — removes the jointing sand that stops pavers moving.
- Window seals and old mortar — both give way sooner than people expect.
Why saying this matters
Plenty of contractors will pressure clean anything you point at, because the quote is easier than the conversation. The problem is that the customer then concludes pressure cleaning does not work, when the truth is it was applied to something it was never going to fix.
A useful quote tells you which parts will come up well, which need a different treatment, and which are not worth doing at all. That last category exists on most jobs.
The short version
If the problem is on the surface, pressure is likely the answer. If it is in the surface — soaked, bonded, alive, or coming from within — it needs something else, and force will remove material rather than the stain.
Not sure which yours is? Read more about what pressure cleaning covers, or request a free quote and we will tell you plainly what will and will not shift.
