Short answer
Those stubborn black spots on a patio are lichen, not dirt — which is why a quick pressure wash never shifts them. The reliable fix is a dedicated patio black-spot remover left to work, then a gentle clean and rinse. For most Chester patios a professional treatment starts from around £150, depending on the size and how established the lichen is.
Why Chester patios get black spots in the first place
Black spots are lichen — a slow-growing organism that bonds tightly into the surface of the stone. They are not loose grime sitting on top, which is exactly why people scrub, jet-wash and bleach them and the spots barely move. The lichen has its roots into the slab.
Our weather here makes it worse. Chester, the Wirral and the Cheshire and Flintshire countryside sit damp for a big chunk of the year, and a patio that is shaded, north-facing, or tucked under a wall or trees stays wet long enough for lichen and algae to settle in and spread. Homes near the Dee, in the older parts of Hoole and Handbridge, and rural properties out toward Wrexham green over especially fast.
The type of patio matters too. Indian sandstone, limestone and other natural stone are porous and lichen loves them; porcelain, concrete slabs and block paving spot up less but still get it in shaded spots. Knowing the surface is half the job, because the wrong treatment or too much pressure will mark the stone permanently.
Patio black-spot treatment — guide prices in Chester & Cheshire
| Job | Guide price | What affects it |
|---|---|---|
| Small patio or path — black-spot treatment | From £150 | Compact area, single surface, easy access |
| Standard patio — treat, clean and rinse | From £225 | Typical rear patio, moderate lichen across the slabs |
| Large or heavily spotted patio | From £350 | Bigger area or established lichen needing a repeat treatment |
| Natural stone (sandstone / limestone) — gentle method | From £195 | Softer porous stone treated and cleaned without harsh pressure |
| Re-sanding block-paving joints (add-on) | From £95 | Where joints have washed out during cleaning |
These are rough guide prices for typical Chester patios. The job is confirmed after a few photos or a quick visit, because the surface type, area, how established the lichen is, and whether a second treatment is needed all change the scope.
How to remove black spots from a patio
- 1
Identify the spots and the surface
Confirm they are lichen — small, flat, firmly stuck black or grey patches — and note your slab type. Natural stone like Indian sandstone needs gentler handling than concrete or block paving.
- 2
Apply a proper black-spot remover
A general patio cleaner or bleach will not do it. Use a dedicated patio black-spot remover, applied to a dry surface on a dry day, and follow the product's dilution. A garden sprayer or watering can gives even coverage.
- 3
Leave it to do the work
This is where most people go wrong — they rush it. The treatment needs dwell time, often hours or overnight, to break the lichen down at the root. Keep pets and children off it while it works.
- 4
Clean off gently, then rinse
Once the lichen has lifted, clean it away with a stiff brush or a low-pressure wash — never a tight, high-pressure jet on natural stone — and rinse the residue thoroughly. Badly established spots usually need a second treatment to fully clear.
Don't reach for a strong pressure washer on natural stone
A pressure washer held too close, or used at a high setting, will gouge and scar Indian sandstone, limestone and older slabs, blow out the jointing sand and force water under the patio. The damage is permanent and far more expensive than the original problem. If your patio is natural stone, the pointing is already crumbling, or the lichen is thick and widespread, stop and get it looked at before anyone turns a lance on it — the right chemistry and a gentle method beat brute force every time.
DIY black-spot removal vs a professional treatment
| DIY | Professional treatment | |
|---|---|---|
| What actually works | Bleach and pressure washing rarely shift true lichen | Dedicated black-spot remover with proper dwell time |
| Surface safety | Easy to scar sandstone or blow out joint sand | Right chemistry and pressure for your slab type |
| Coverage | Patchy results and spots left behind | Even treatment across the whole patio |
| How long it lasts | Spots often return within a season | Treated at the root, with advice on keeping it off |
| Typical cost | £15–£40 of product, plus your time and the risk | From £150, insured, with a finished result |
Frequently asked questions
Why won't my pressure washer remove the black spots?
Because they are lichen, not dirt. The lichen is bonded into the surface of the stone, so blasting it only cleans around it — and on natural stone a strong jet can permanently mark the slabs. It needs a dedicated black-spot treatment to break it down first.
Does bleach get rid of black spots on a patio?
Not reliably, and we don't recommend it. Bleach can lighten the spots briefly but rarely kills the lichen at the root, it can discolour natural stone, and the run-off harms borders, lawns and drains. A proper patio black-spot remover is safer and far more effective.
How long does a black-spot treatment take to work?
The treatment itself is quick to apply, but it needs dwell time to work — often several hours or left overnight. Heavily established lichen frequently needs a second application a week or two later to clear fully.
Will the black spots come back?
They can, especially on a shaded, damp, north-facing patio in our climate. Keeping the area swept, letting in light where you can, and a periodic treatment keep them at bay. Sealing some surfaces afterwards also slows regrowth.
Is it safe to treat black spots on Indian sandstone myself?
You can, but carefully — sandstone is soft and porous, so use a sandstone-safe black-spot remover, never strong pressure, and test a hidden corner first. If the patio is large, valuable or badly spotted, it's worth having it done professionally to avoid marking the stone.