Patio Cleaning: Getting Stone, Slabs and Decking Back to Life

Identify the material first

Indian sandstone is by far the most common UK patio material and is moderately soft and porous. Limestone is softer still and reacts badly to acidic cleaners. Slate is durable but delaminates if hit hard with pressure. Porcelain is dense, non-porous and effectively immune to staining but can be scratched. Concrete slabs vary from very robust to surprisingly friable when older.

If you are unsure, a simple test helps: drip water onto a clean area. If it soaks in and darkens the stone within seconds, the material is porous and needs a gentle approach plus sealing. If it beads and sits, you have porcelain or a sealed surface and can be more robust.

The right cleaning method by surface

For sandstone, limestone and older concrete: low to moderate pressure with a rotary flat-surface cleaner, or a soft wash with a biocide and a stiff brush where the stone is very soft. Never hold a lance close to the surface — it will pit soft stone in seconds and the marks are permanent.

For slate and porcelain: gentle cleaning with detergent and a brush is often all that is required, followed by a rinse. For timber decking: low pressure only, working along the grain, then a biocide, because decking algae is a genuine slip hazard and it lives in the grain rather than on top of it.

• Sandstone / limestone: rotary at low pressure or soft wash
• Slate: brush and detergent, avoid direct high pressure
• Porcelain: detergent, brush, rinse
• Concrete slabs: rotary cleaner, moderate pressure
• Timber decking: low pressure along the grain, then biocide

Dealing with specific stains

Black spot lichen on sandstone is the hardest common problem. It bonds into the stone and general cleaning will not shift it; it needs a dedicated lichen treatment with dwell time, sometimes repeated. Realistically it fades substantially rather than vanishing on the first application.

Leaf tannin staining, the brown blotches under trees, usually responds to an oxygenated cleaner. Barbecue grease needs degreasing before any water is applied, or the pressure simply drives it deeper. Efflorescence — the white bloom on new paving — is mineral salts working out of the slab and generally weathers away over the first year or two.

Joints, weeds and re-pointing

Weeds growing between slabs indicate failed pointing, not just seeds. Cleaning will strip out loose, crumbling mortar and reveal how much of the pointing has actually gone, which is a good thing — you can then repoint properly rather than sealing over a failure.

For slab patios, re-point with a suitable jointing compound once the surface is fully dry. For block-paved or setts-style areas, brush in kiln-dried sand. Skipping this stage leaves open joints where water sits and weeds re-establish within a season.

Cost, sealing and frequency

UK patio cleaning is generally £3 to £7 per square metre, so a typical 25m² patio commonly costs £120 to £220. Add repointing where needed, and sealing at roughly £5 to £12 per m². A biocide treatment after cleaning is inexpensive and does far more for longevity than most people expect.

Sealing porous stone is genuinely worthwhile: it resists staining, reduces algae grip and makes the next clean far easier. Most sealers need renewing every three to five years. With a seal and an occasional biocide, a patio typically needs a full clean only every two to three years.

The bottom line

The mistake we are called out to fix most often on patios is not dirt but damage: a hand-held lance held too close to soft Indian sandstone, leaving permanent pitting and lance tracks that no amount of subsequent cleaning will disguise. If you are cleaning it yourself, keep the nozzle well back, keep it moving, and test on an out-of-sight corner first.

For a patio you actually want to use, finish the job properly: repoint the joints once the surface is dry, apply a biocide, and seal porous stone if you can catch a settled dry spell. That sequence turns a clean patio into a low-maintenance one, and it is the difference between doing this every year and doing it every three.

Frequently asked questions