RogerT wrote:
Having spent a couple of days getting wet whilst trying to clean the
summer's accumulation of green/black algae/gunge/dirt from the
concrete patio slabs with a pressure hose, I'm sure there must be an
easier way.

Not really, although doing it with a stiff brush and some fairly strong
detergent will have the same outcome, I don't think it's much easier if you
have a large are to do.


Apart from paying someone else to do it, is there either an easier or
more permanent way to achieve the "new whiteish-grey slab" look?

see above, you need washing soda or something else alkali and fairly strong,
I don't reccomend caustic soda though, although they will look like brand
new when finished, the chemical, toxicity and danger implications outweigh
the benefits.

Does the use of a pressure hose take the surface off the slabs and
eventually damage them beyond use?

No, they are concrete and unless they are already damaged in some way, water
is not going to have any effect on them, well not in your lifetime anyway,
unless you plan on outliving the Galapagos Tortoise on todays news.