Why sandstone is easy to get wrong
Sandstone is a natural stone, not a manufactured product. Two patios laid the same year can behave completely differently under cleaning because the hardness, grain and surface finish vary. A method that suits a hard-wearing concrete slab can leave lines, furring or a patchy finish on sandstone, and once the face of the stone is damaged that is permanent.
Condition matters as much as the material
Age on its own is not the problem. What matters is the state of the patio now: whether the surface is already flaking, whether the pointing is crumbling, whether slabs are loose, and whether it has been sealed, treated or cleaned harshly in the past. All of that changes how the stone responds and what a sensible result looks like.
Pressure is only part of the job
People tend to picture a lance and a lot of pressure. In practice the outcome depends on how the surface is prepared, what equipment is used, how far the nozzle is held from the stone, how evenly it is worked and how the area is rinsed down afterwards. Turning the pressure up is usually the quickest way to damage a patio, not to clean it better.
What to tell whoever is quoting
- Whether you know the patio is natural sandstone, and roughly how old it is.
- Whether it has ever been sealed or treated, and if so with what.
- Whether it has been pressure washed before, and how it looked afterwards.
- Any loose, cracked or rocking slabs, and the state of the pointing.
- Specific marks you are hoping to shift, with a close-up photograph in daylight.
What a clean will and will not do
General dirt, algae, moss and organic build-up usually come away well, and most sandstone patios look far more even afterwards. Permanent staining, deep weathering, existing damage and failed pointing will still be there. Complete black spot removal is not something anyone should promise from a photograph.
Please do not experiment with chemicals
There is a lot of advice online recommending household mixtures on natural stone. Some of it will bleach, etch or permanently discolour sandstone, and no instructions of that kind are given here. If you are unsure, ask before you try anything.
Getting it checked
More detail is on the sandstone patio cleaning page and the patio cleaning service page. Send a few daylight photographs and your postcode and you can request a written quote with an honest view of the likely result.