The 5 Methods Compared
There are five proven ways to clean patio slabs. The right one depends on your slab material and what you are trying to remove. Start with the gentlest method that will work. For more inspiration, see our patio ideas and costs guide.
| Method | Best for | Cost | Risk level |
|---|---|---|---|
| Pressure washer | General grime on concrete slabs | £0 (owned) to £40/day hire | Medium: can damage pointing and soft stone |
| Proprietary patio cleaner (Patio Magic, Algon) | Algae, moss, lichen; all materials | £8 to £20 per bottle | Low when used as directed |
| Sodium hypochlorite solution | Black spot lichen, heavy staining | £5 to £15 | Medium: kills plants, bleaches fabrics |
| Stiff brush + soapy water | Light dirt, regular maintenance | Under £5 | Very low |
| Natural (vinegar, baking soda) | Light stains on robust surfaces | Under £5 | Low, but avoid on limestone |
Method 1: Pressure Washing
The fastest option for concrete and porcelain slabs. Use a fan nozzle, keep it at least 30cm from the surface, and work at a shallow angle. Never use a pinpoint jet on sandstone or limestone: it etches the surface. The biggest risk is blasting out the pointing between slabs, so expect to re-point afterwards. A rotary patio cleaner attachment gives a more even finish with less damage.
Method 2: Proprietary Patio Cleaners
Products like Patio Magic and Algon are the safest choice for most homeowners. They kill algae, moss and lichen at the root rather than just blasting the surface, so results last longer (typically 6 to 12 months). Apply on a dry day, leave for the stated dwell time, and rinse. They cost more than bleach but are formulated to be plant-safe once dry when used as directed.
Method 3: Sodium Hypochlorite
The professional’s choice for black spot lichen, the stubborn black dots that survive pressure washing. Dilute to around 4:1 water to hypochlorite, apply with a watering can or sprayer, leave 30 to 60 minutes, then rinse thoroughly. Pre-wet surrounding plants and cover delicate planting: hypochlorite kills vegetation on contact. Wear gloves and eye protection, and never mix with acids.
Method 4: Stiff Brush and Soapy Water
For lightly soiled patios and regular maintenance, a stiff yard brush with warm water and washing-up liquid is enough. It is the only method with zero risk to any material, and it is ideal for porcelain tiles, which rarely need anything stronger. Work in sections and rinse as you go.
Method 5: Natural Methods
White vinegar (neat, left 30 minutes) shifts light algae and mineral deposits on concrete and porcelain. Baking soda paste works on grease spots. Do not use vinegar on limestone or marble: acids etch calcium-based stone permanently. Natural methods are fine for maintenance but will not touch black spot lichen.
Material Safety Matrix
| Material | Pressure washer | Bleach / hypochlorite | Vinegar / acids |
|---|---|---|---|
| Concrete slabs | Yes, fan nozzle | Yes, diluted | Yes |
| Porcelain tiles | Yes | Yes | Yes |
| Sandstone | Careful: low pressure only | Yes, diluted | Avoid |
| Limestone | Avoid high pressure | Yes, diluted | Never |
| Granite setts | Yes | Yes | Yes |
Stubborn Stains: Specific Fixes
Black spot lichen
The black dots with tiny root-like structures (hyphae) that laugh at pressure washers. Sodium hypochlorite is the reliable fix; proprietary lichen removers work more slowly. Expect two treatments for established colonies.
Green algae and moss
Patio Magic or Algon, applied in spring. Improve drainage and sunlight where possible: algae returns fastest in damp, shaded corners.
Grease and oil (BBQ stains)
Baking soda paste or a dedicated degreaser, scrubbed in and left for an hour. Porous sandstone may need two rounds.
Rust marks
Oxalic-acid-based rust removers from DIY stores. Test on a hidden slab first, as they can lighten some stones.
Efflorescence (white powdery bloom)
Usually harmless salts migrating out of new slabs. Brush off dry; it typically fades within a year. Do not seal over it.
Prevention: The Seasonal Calendar
- Spring: full clean (choose your method above); treat algae-prone areas; re-point damaged joints
- Summer: sweep weekly; spot-treat BBQ grease promptly
- Autumn: clear fallen leaves (tannin stains); apply preventative patio cleaner before winter
- Winter: avoid de-icing salt on natural stone; brush off debris to stop moss taking hold
Mistakes That Damage Patios
- Pressure washing sandstone or limestone on full power (etches the surface permanently)
- Using bleach near lawns and borders without pre-wetting plants
- Sealing a damp patio (traps moisture and causes flaking)
- Ignoring the pointing: a clean patio with crumbling joints still looks tired
- Using vinegar or acidic cleaners on limestone and marble
Patio Cleaning FAQs
What is the best way to clean patio slabs?
For most UK patios, a proprietary patio cleaner (Patio Magic or Algon) gives the best balance of effectiveness and safety. Pressure washers are faster but risk damaging pointing and soft stone.
How do I remove black spot from patio slabs?
Use diluted sodium hypochlorite (around 4:1 water to chemical), leave 30 to 60 minutes, then rinse. Two treatments may be needed for established lichen.
Will a pressure washer damage my patio?
It can. High pressure etches sandstone and limestone and blasts out jointing sand. Use a fan nozzle, keep 30cm distance, and avoid pinpoint jets.
Can I use bleach on patio slabs?
Yes, diluted sodium hypochlorite is effective, but it kills plants on contact. Pre-wet surrounding vegetation, wear protection, and rinse thoroughly.
How do I clean outdoor porcelain tiles?
Porcelain is tough and non-porous: a stiff brush with soapy water usually suffices. For algae, use a proprietary patio cleaner. Avoid harsh acids unnecessarily.
How often should I clean my patio?
A full clean once a year in spring, with a preventative treatment in autumn, keeps most UK patios looking good. Shaded, damp patios may need twice-yearly attention.
Does vinegar clean patio slabs?
White vinegar handles light algae and mineral deposits on concrete and porcelain, but never use it on limestone or marble, which acids damage permanently.
How do I stop algae coming back?
Apply a preventative patio cleaner each autumn, improve drainage, trim overhanging plants for sunlight, and sweep regularly so organic matter does not build up.
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