On 08/11/2020 10:42, Ian wrote:
On 07/11/2020 14:54, The Natural Philosopher wrote:
On 07/11/2020 14:17, F wrote:
On 07/11/2020 09:37, The Natural Philosopher wrote:
On 06/11/2020 20:59, F wrote:

We've got a patio made up of light coloured concrete paving slabs
with a slightly rough texture. I've used a Karcher power washer to
remove the compost that the resident gardener has managed to tread
into them but there's a green stain (algae?) that's pretty resistant
to removal.

Anyone got any suggestions on what might shift it?

Green goes with bleach and heavy power washing. Its the black ones that
are impossible to shift.

We have black too. Forgot to mention that.

If BAC50 shifts it, please let us know. I've tried everything

have you tried thin bleach as demonstrated on various Youtube videos
although many example swimming pool chlorine.

I have had a huge amount of black and green lichen on concrete pavers and
simply brushed on the bleach over a slightly dampened surface on a sunny
day and kept it damp for the rest of the day. If no kids or pets around
I left it and 98% has gone in one or two sessions. Exception is the
crumbly edges which are a bugger.

Add a couple of drops of washing-up liquid to a watering-can of diluted
bleach, and stir it in. The idea is to avoid making it foam, you just
need it to be evenly distributed throughout the bleach solution. It
lowers the surface tension, enabling the bleach solution to penetrate to
places where the high surface tension of water would otherwise limit the
penetrating power of the solution.

Oddly, as mentioned in one video, it seems to go on having an effect for
a while afterwards. Good luck

When the solution dries out, the active ingredient is still there,
re-dampening the treated surfaces or a shower of rain will reactivate it.

Dilute bleach, especially with added washing-up liquid, will kill black
spot and brown spot invasions; it might kill white spot too but the
remains seem to persist.

Unfortunately it doesn't get rid of the blackened areas.

--
Spike