Particularly at this time of year think this is unlikely to be any insect could you add a photo to your question?

Any overhanging trees nearby? Or large shrubs,specially ones with black or purple berries?

We had the Indian stone patio laid about 3years ago & the black spots started to appear 2years ago. There are no overhanging shrubs, it really gets worse in spring and summer which made me wonder if it is an insect. The stone was cream colour but now it is turning blackish with all the spots (there are thousands of small spots now!)

This is iron or rust within the stone that is coming out. We laid an Indian stone patio at the front and that isn't the same colour it was when we laid it but it doesn't worry us.

The patio is really dirty looking compared to its original state. This black spot started on one slab & continued to spread to the slabs nearby & now every slab is totally covered. It is so bad, if I can't find anyway to clean it & get rid of these spots, the entire area will have to be lifted and reset using something else. But the problem would still be there. I would like to know if this has happened to anyone else. As I said previously, the black spots are now also in the garden ornaments & the cream gravel so it is unlikely to be something coming out of the stone. It's obviously just attacking the SOFT STONE & not the brick walls or blockpaving.

could it be a type of mould or fungus?

No it is not mould or fungus, because the pressure washer would have removed it.

Thankyou all for your help, maybe I will hopefully get it resolved before next spring.

Willows did you read my comment? This is iron or rust coming out of the stone and there is nothing you can do to stop it!

Some Indian sandstone slabs have 'fossil fern leaves' as an added attraction. These are not fossils but iron oxide patterns in the stonework. The Indian sandstone is a cheap sandstone and is imported into this country as ballast in ships, then sold on as attractive paving. The sandstone contains a lot of iron which can manifest as 'fossils' or, in your case, as rusty spots.

Willows, try cleaning your patio with Armillatox. Water a solution on the whole area with a can with a coarse rose, gloves and a mask are needed when applying the mixture. It will be safe to go on it when the smell has gone, heavy rain will do the rest, avoid freezing conditions.

if its on stone stautues etc what about one of the small lichens, that will appear and are stubborn to remove. could be fungal, again not all come off easily, even with a jet washer.

This is one of the lichen/fungus - common with cheaper forms of the indian sandstone and other slabs. It arrives on the imported stone and spreads to anything containing a mineral it can grow on - hence stone statues will be affected but block paving will not. This web-site is a real eye-opener, and the link to black spots is here: http://www.pavingexpert.com/maintain_03.htm. They recommend brushing everything down with common diluted bleach, but not the glutinous kind. Very interesting site.

Thank you for that information Avkg47, I found it most interesting.

Thankyou very much Avkg4 this is very helpful indeed.

I use the Patio Black Spot Remover from the Patio Black Spot Removal Company.