The short answer
A stiff brush, hot water with washing-up liquid or soda crystals, and a patio cleaner for the green growth. Slower, far safer, and the result lasts longer.
- Sweep thoroughly and pull weeds out of the joints first.
- Wet the surface, then apply hot water with soda crystals or a dedicated patio cleaner.
- Leave it to dwell for the time on the label.
- Scrub with a stiff brush and rinse.
- For green algae, use a patio cleaner containing a biocide, which prevents regrowth for months in a way that blasting does not.
What will ruin it
Do not use bleach on paving near planting, and never mix a patio cleaner with anything else. Runoff goes into the soil and into drains, so check the label for what is safe near plants and ponds.
Why it works
Green growth on paving is living, so removing it physically leaves the spores behind and it returns within weeks. A biocide kills it, which is why chemical cleaning lasts far longer than blasting.
Household chemicals can be dangerous in combination. Never mix them, keep the room ventilated, and test anything on a hidden patch first. Full disclaimer.