In short
Often you can, with care. The Royal Horticultural Society says to use a pressure washer with care where drainage is poor, because the extra water can make damp problems worse, and that a pressure washer may damage loose stones and cause waterlogging. Moss and algae also come back if the conditions stay the same, and they make surfaces slippery, so it is worth managing them on anywhere you walk.
This is a job for our Exterior cleaning service.
What the RHS says
- Use a pressure washer "with care in areas where drainage is unsatisfactory as the extra water could exacerbate damp problems".
- It "may damage loose stones and cause waterlogging as well as using precious water".
- The RHS suggests a stiff brush as an alternative on floor surfaces.
- Growths "will return if conditions remain the same".
Why bother
The RHS notes that algae, lichens and moss can make hard surfaces slippery, and advises preventing or managing their growth on surfaces that are walked on. A clean patio is a safer patio.
Chemicals
The RHS says most moss and algae products are non-persistent and repeat applications will be needed, and advises caution when using chemicals.
Where the water goes
Government guidance for businesses says surface water drains discharge directly to the environment, so contaminated wash water from a business should not go down them. That guidance is written for businesses rather than householders, but it is a good reason to keep detergent off the road and out of the gutter.
Test first
Because the RHS warns about loose stones, try a small patch out of sight first, keep the nozzle moving and do not blast joints. If the surface is soft, old or laid on poor drainage, brush it instead.
If you would rather someone else did it
If you would rather ask someone else, SAS Cleaning's exterior cleaning covers windows, driveways, patios and decking in Wisbech and across the Fens. Tell us what the surface is made of, send a photograph and ask whether we can help through the enquiry form.