Patios & Paving · Problem & repair
Slippery moss and black algae on patios and paths
A green film on paving is a safety problem in autumn and winter, and the usual reaction - a hard blast with a pressure washer - can do real damage to the surface it is cleaning.
Matching the cleaning method to the material is the difference between a patio that looks refreshed and one that looks scoured.
How to tell this is your problem
- Green or black film, worst in shade and under trees
- Slippery underfoot after rain or dew
- Stubborn black spots that scrub off in flecks
- Growth concentrated where water lingers
- Return within months of the last clean
Repair or replace?
Pure maintenance. No paving needs replacing because of algae - though persistent regrowth usually points at a drainage detail worth fixing.
Repair options, cheapest first
- 01
Soft wash with a suitable treatment
A patio-safe biocide applied and left to work kills the growth at the root, then rinses away. Gentler and longer-lasting than blasting.
- 02
Controlled pressure washing
Effective on concrete and block at moderate pressure with a fan tip kept moving. Natural stone and porcelain need care and lower settings.
- 03
Improve drainage and light
Correcting a flat fall, trimming back overhanging planting and clearing gutters removes the conditions the growth needs.
- 04
Re-sand or re-point afterwards
Any wash removes joint material. Replacing it is part of the job, not an extra.
Why it happens
Shade and poor air movement
Surfaces that never fully dry out stay biologically active all year.
Standing water
Where the fall is flat or reversed, water sits and provides a permanent growing environment.
Organic debris
Leaf fall and overhanging planting deposit the nutrients that moss and algae need.
Porous surfaces
Open-textured stone and concrete hold moisture in the surface, which suits algae far better than a dense porcelain.
Cost and time on site
Indicative cost
Cleaning is priced per square metre; treatments and re-sanding are usually included in a proper quote.
Typical duration
Most patios and paths are cleaned within a day.
Every quote is priced after seeing the site. Book an autumn clean before the surface gets slippery.
Moss & algae on patios: common questions
- Is bleach safe on patio slabs?
- It can discolour some stone and harm nearby planting. A purpose-made patio biocide is safer and works on the organism rather than just lightening it.
- How often should a patio be cleaned?
- Once a year is typical in shaded gardens; every couple of years is often enough in open, sunny positions.
- Will sealing stop moss returning?
- Sealing reduces porosity so growth is easier to remove, but shade and standing water will still allow it to establish.
- Can pressure washing damage paving?
- Yes. Too high a pressure or a pinpoint nozzle can etch stone, strip concrete surface and blow out joints. Technique matters more than power.
Services that fix this
Ready to transform your outdoor space?
Free site visits and no-pressure quotes within a 30-mile radius of Ash Vale - covering Surrey, Hampshire and Berkshire.