You can clean a patio properly without a pressure washer — and sometimes that’s the safer choice, especially if joints are already weak.
RHS advice on algae/moss/lichen on hard surfaces focuses on regular brushing, removing growth from cracks, and preventing damp/shade conditions from letting it take hold.
BBC Gardeners’ World also covers cleaning patios with or without a pressure washer.
Step 0 — What are you trying to remove?
- Green film = usually algae
- Tufty green growth = moss
- Black/white spots = often lichen (stubborn)
RHS notes moss thrives in damp, shady conditions on hard surfaces and commonly grows in cracks and edges.
Method A: Clean patio slabs WITHOUT a pressure washer
Step 1 — Sweep and dry-brush first
Remove debris/leaves
Scrub with a stiff broom/brush
RHS recommends brushing hard surfaces and doing it regularly to prevent growths establishing.
Step 2 — Clear cracks properly
Use a pointed tool/old knife for moss in joints
RHS explicitly recommends this approach for moss in paving cracks.
Step 3 — Wet clean + rinse
Use a patio-appropriate cleaner and follow label directions.
BBC Gardeners’ World provides guidance on cleaning patios without pressure washers as well as with them.
Step 4 — Let it dry fully
Drying is key. A patio that stays damp will re-green faster.
Method B: Clean patio slabs WITH a pressure washer
Step 1 — Start low pressure and keep moving
Don’t drill one spot
Keep the nozzle moving
Avoid blasting directly into joints
Step 2 — Expect joint disruption on some patios
Many patios need touch-ups after jet washing.
Step 3 — Safety basics
High-pressure water can cause serious injuries. Industry safety guidance treats high-pressure water jetting injuries as emergencies.
How to stop it going green again quickly
RHS notes these growths thrive where it’s damp and shady, so prevention is about:
sweeping leaves off
brushing periodically
improving drainage/runoff where water sits