Patio black marks

2stixoftwixes

Just under a year ago, we had a new patio fitted. 

In the late summer about 50% of the slabs have developed slightly greasy looking big black marks at random areas which haven't gone away
I have spoken to the person who laid it, who in turn has spoken to the supplier, who have said that the problem is
(Exactly word for word)  "differential weathering it will fade in time, but might not completely go away"

The supplier has offered our patio installer (therefore us) a refund of 3 packs which I'm guessing is around £600 
However, if we take the refund we are still left with an ugly looking patio that cost us nearly £3000
I'm not worried about the refund, I want a nice-looking patio

I have attached some photos

Obviously, we know that it isn't the patio installer's fault, as he bought faulty paving slabs, but we paid him for a nice patio, and it's not looking very nice at all

Our patio installer hasn't replied to our latest emails - where we state we are not happy to take a refund and would like it fixed
We don't know where to go from here, or what the next step should be

I know the small claims court, but to get it looking nice would mean ripping it up and starting again

Any advice?

photome

They look like natural stone slabs where you will get imperfections. You could have them replaced and still end up with similar/same imperfections.

Just to add I am not an expert that’s just my opinion after having a natural stone patio laid a couple of years ago

Aylesbury_Duck

Do they look like that even after a long dry period?  From the photos, the patches look wet or damp.  I have a similar phenomenon on mine, where after rain, as the slabs dry, some patches and in some cases whole slabs, appear damp for hours after others.  I quite like the effect to be honest, and it's inevitable with a natural product.

Keep_pedalling

You will always get some form of organic growth on slabs (lichens, algae and moulds) especially on rough services on semipermeable rock. This is part of the weathering process the stone is not faulty. 

If it is slimy then a jet wash will remove the slime but the stain may remain if it he’s penetrated the rock. 

sheramber

The black marks are black lichen. The spores settle on the stone  and feed off the  minerals in the stone.

Do a Google search for 'black marks on natural stone patio'.

cx6

What was the original contract? Was it 'supply and fit' in one contract (in which case the installer is responsible for everything) or was it fit-only, with the installer buying the stones as your agent (in which case you are responsible for the stones, the fitter for the fitting).

The second option is very common in eg carpet laying - for obvious reasons

mobileron

Try some bleach and scrubbing brush, worked on mine

pulliptears

Try watering the areas with patio magic, it's an inexpensive thing to try at about a tenner a bottle (will last ages just on those bits as well).  The stuff is pure witchcraft.

photome

Just been out for a walk, noticed a footpath ( to someone’s house) that looked exactly like your patio, same colour slabs and same black markings.

I second patio magic…i used it last spring couldn’t believe the results with zero effort