Short answer
To clean a patio without damaging it: clear the surface, treat the moss and algae first, then wash at a low-to-moderate pressure suited to your paving — never blast delicate stone up close. Sweep kiln-dried sand back into the joints when it dries. On Indian sandstone, porcelain or old crumbling pointing, go gentle or get it looked at before you turn a lance on it.
Why patios green over so fast in Chester
Patios in Chester, Cheshire and the Wirral take a beating from our weather. The ground sits damp for most of the year, north-facing patios behind a house barely catch the sun, and anything under trees or near the Dee greens over within a season. That slippery green film and the black spotting on the slabs are living growth — not just dirt — which is why a quick blast in spring is back looking tired by autumn.
The other thing that catches people out is the paving itself. A lot of Chester homes have older concrete flags or block paving that copes with pressure, but plenty of newer extensions and landscaped gardens around Hoole, Handbridge and out toward Tarporley and the Wirral have Indian sandstone or porcelain. Those softer, more porous surfaces mark and pit easily, and the wrong technique can ruin them in seconds.
Get the method right and a patio comes up beautifully and stays clean for far longer. Get it wrong and you can strip the surface off the stone, blow the jointing out, and be left with a patchy, striped mess that costs more to put right than a proper clean would have.
How to clean a patio, step by step
- 1
Clear it and sweep it down
Move the furniture and pots off, pull any obvious weeds out of the joints, and give the whole patio a good stiff-brush sweep. Getting the loose moss and grit off first means you are cleaning the stone, not pushing slurry around.
- 2
Treat the growth and let it work
Apply a patio-safe algae and moss treatment and give it the time it says on the tub — usually a day or two. This kills the growth at the root so it lifts properly, instead of you blasting the green off the top and watching it come straight back. Keep treatments off planted borders and lawns.
- 3
Wash at the right pressure for your surface
Start gentle and keep the lance moving and at an even distance, working in overlapping passes so you do not leave stripes. Concrete and block paving take more pressure than soft stone. On Indian sandstone or porcelain, ease right off and never hold the nozzle close — those surfaces pit and scar fast. A patio cleaner attachment gives a far more even finish than a bare lance.
- 4
Rinse, dry and re-sand the joints
Rinse the residue away toward a drain, not into your borders, then let the patio dry out. On block paving and jointed slabs, brush dry kiln-dried sand back into the gaps once it is bone dry — that locks everything together and slows the weeds coming back.
DIY kit vs a professional clean — what it costs
| Job | Guide price | What affects it |
|---|---|---|
| DIY: hire a pressure washer for the weekend | From £40 | Plus treatment, sand and your whole day — and the risk to soft paving |
| Professional small patio or path clean | From £125 | Compact area, single surface, easy access |
| Standard patio clean + re-sand | From £175 | Typical rear patio, moss and algae removed, joints re-sanded |
| Heavy black-spot and weed pre-treatment | From £45 | Where growth is established and needs treating before washing |
| Delicate stone (Indian sandstone / porcelain) clean | From £150 | Gentler method to protect softer, more porous surfaces |
Treat these as guide prices for typical Chester patios. The job is confirmed after a few photos or a quick visit, because the surface type, area, level of growth and whether you want re-sanding all change the scope.
When to put the pressure washer down
A pressure washer held too close, or on too high a setting, will strip the surface off Indian sandstone, blow the jointing sand out, force water under the slabs and lift loose paving. If your pointing is already crumbling, the slabs rock underfoot, or you are not sure how your stone will react, stop. On delicate or failing paving the damage is real and expensive to fix — far more than the clean would have cost. Get it looked at first.
DIY patio clean vs a professional clean
| DIY with a hired washer | Professional clean | |
|---|---|---|
| Finish | Easy to leave stripes, swirls and patchy slabs | Even, consistent finish across the whole patio |
| Surface safety | Real risk of scarring soft stone or blowing out joints | Right pressure and technique matched to your paving |
| Regrowth | Moss and weeds often return within weeks | Pre-treated growth and re-sanded joints slow it right down |
| Effort and mess | Hours of hard work, soaked and covered in slurry | Done in one visit, area cleared and left tidy |
| Typical cost | From £40 hire, plus your day and the risk | From £125, insured, with a finished result |
Photos that get you an accurate price fast
- A wide photo of the whole patio so the area and layout are clear
- A close-up of the worst patches — black spots, thick green algae, or weeds in the joints
- A photo showing the surface type (sandstone, porcelain, concrete, block paving) and how the patio is accessed
Frequently asked questions
Can I jet wash an Indian sandstone patio?
Only with great care. Sandstone is soft and porous, so a high-pressure jet held close will pit and scar it. Use a low setting, keep the nozzle well back and moving, or have it cleaned with a gentler method. If in doubt, get it looked at first — the damage is permanent.
How often should I clean my patio in Chester?
Most patios benefit from a clean every one to two years. Shaded, north-facing or tree-lined patios in our damp climate green over faster and often need doing yearly to stay on top of it.
Will the moss and weeds just come straight back?
Not if it is done properly. Pre-treating the growth so it dies at the root, rather than just blasting the surface, and re-sanding the joints afterwards makes it much harder for moss and weeds to take hold again.
Do I need to re-sand the joints after cleaning?
On block paving and jointed slabs, usually yes. Cleaning lifts the old sand out of the gaps, and that sand is what locks everything together and helps keep weeds down. Brush dry kiln-dried sand back in once the patio is fully dry.
What is the black spotting on my slabs and can it be removed?
Black spot is a stubborn lichen that grips the stone and will not shift with a normal wash. It needs a proper treatment to break it down. It can be removed, but it takes the right product and patience rather than brute pressure.
Sources & further reading