Removal of unknown marks on old paving - Is removal possible

[peteuk]

Thank you for your help with my post regarding the failed edge course on my drive. I asked someone to give me a price for the repair yesterday, and also mentioned dark stains on another part of the drive.

He said he could guarantee to remove the stains using an industrial jet wash and 'hypochlorite' - I assume Sodium hypochlorite. I looked this up and read it will remove algae etc but I don't know what the stains are, or how old they are - we noticed them about a year ago but we had had many workmen here after purchase. The drive was installed by the previous owners many years ago.

They go across both sides of the drive as well as the middle so don't look like they're caused by an oil leak. Maybe they are some kind of mastic or diesel but we can't tell.
Please see attached link for photographs.
https://1drv.ms/u/s!Ao8_zjrfOGe3gdpzkB9tQD-YrXAIzg?e=mxaeda

Unfortunately it started to rain when I took the photos but you can see the 'larger' dark patches I hope.

Should I allow the contractor to 'have a go'? (The drive has been jet washed but only with water previously).

I am not hopeful having read this site, and not knowing what the stains are but can anyone else advise a solution? (The blocks are old so replacing blocks is an option but they will not colour match).

Thank you for help.

Pete

[RAPressureWashing]

Looking at the photos, I'd say you have some lichen on the paving, but the larger spots might or might not be lichen, but could be, you could try a bleach mix yourself on a couple of pavers to see it it comes off, if yes then you know it's organic (lichen etc) so a hypo was by the contractor should then get the paving clean. If they don't come off then the next thing is a de-greaser to see if they are an oil stain. It won't be diesel from the photos, the size of the spots is to small and diesel/petrol etc usually spreads it's self.

[peteuk]

Thank you, R&A
For info I believe the small spots you can see are raindrops due to my bad timing with the weather.
I hope no-one thinks I have wasted their time (I shall see if I can close this post) but a different contractor came today and following discussions I am going to have a new drive laid. This will solve this issue and the previous post regarding the edge course.

Once again, thank you for this wonderful site.