The method, on awkward Stroud drives
Why controlling the water matters more here than the pressure does.
Plenty of firms turn up with a pressure washer and treat every drive the same — flat or steep, stone or block, it all gets the same lance held the same way. In most of the county you can half get away with that. In Stroud you can't, for two reasons, and both come back to water.
First, the stone. The dominant surface across the old town and up the valleys is Cotswold-stone setts and slabs — a porous, split limestone, not a hard engineered block. Drive a high-pressure jet at that and you don't just shift the algae; you pit the open grain, wash the jointing out from between the setts, and leave the surface rougher than you found it so the green comes back quicker than ever. So on stone we drop the pressure right down, work with a gentle fan and stone-safe treatment, and let the chemistry do the lifting rather than brute force. The honey colour comes back, the slip hazard goes, and the stone is left intact.
Second, the slope. A drive you could hose flat in Quedgeley might fall two metres towards the road at Rodborough or Uplands, with a neighbour's plot directly below. Wash that top-down without a plan and the dirty silt-laden water sheets straight onto the highway or down next door's drive — which is a mess, a complaint, and on a public road a genuine pollution issue. So we work the slope in controlled sections, lay matting and bunding to catch and channel the run-off, and vacuum or sweep the slurry up as we go rather than letting it run. It's slower, it costs more in time than a flat drive, and we price the job knowing that. But it's the only honest way to clean a steep valley drive.
On block paving the principle is the same — restore, don't just rinse. The rotary surface cleaner gives an even finish with no zebra-stripes, but cleaning always flushes the kiln-dried sand out of the joints, so we brush fresh sand back in as standard once it's dry. Skip that and the joints sit open, the weeds come straight back, and the blocks start to creep. Re-sanding is what turns a clean into a lasting one.