The slip risk on a patio is almost never the moss you can see - it is the thin black or green film you can feel underfoot when it is wet. That film is biological, and it is why a slab that was fine in July becomes hazardous in November.
The finger test
Rub a wet slab with a thumb. If it smears green or black and leaves a shine, you have an active algae film. Grit and dry dirt do not smear like that.
This guide sits under our Patios & Driveways work, covering 20-mile radius of Plymouth.
Cleaning without wrecking the slab
Indian sandstone, porcelain and pressed concrete all tolerate different pressures. We choose the pressure to the slab and treat the biology chemically rather than trying to blast a living film off stone.
Keeping it safe
Clearing the joints and getting water off the surface matters as much as the clean. Shaded, badly drained patios come back faster and need a shorter cycle.
Questions we get on this
- Will jointing sand wash out?
- Some will on a heavily degraded joint. We flag it beforehand and can re-sand as part of the job.
- Is it safe around pets?
- Yes, once rinsed and dry. We tell you how long to keep the area clear on the day.
- How often for a shaded patio?
- Every twelve to eighteen months keeps a north-facing patio safe; a sunny one lasts longer.
Related reading
- Is sealing a driveway worth the money?
- Why render turns green - and how to clear it for good
- Black streaks running down walls: what causes them
- Moss on roof tiles: when it matters and when it does not