On Friday, 8 June 2018 15:59:40 UTC+1, F wrote:
I've used my Karcher K2.59 pressure washer (1300 psi) with the high
pressure lance on some red/brown and beige block paving but it's not
removed all of the black mildew-style staining or much of the blobs of
green lichen(?).

How can I get it cleaner than this? Does it need a detergent (the
Karcher has a detergent container but that doesn't work with the high
pressure lance attached), or do I need a more powerful pressure washer
(recommendations?), or something else?

It did come with a circular rotating nozzle assembly but that is
reluctant to spin and is basically a waste of space.

--
F

I have exactly the same problem.
Tried all sorts of stuff,(including bleach)
Nothing seems to shift the black stuff.
It seems to have got right into the concrete.

I have concluded that using light coloured blocks is a bad idea.