What is causing green/dark growth on exterior chimney wall and how to treat?

suebfg

Our house is a corner house and on the exterior of the chimney breast, there seems to be a darker patch of green/black- can't really think of how to describe it.

My husband thinks it is just the weather however it is only on the chimney breast. The previous owner had removed the fire and it is now covered over with plasterboard and not used.

There is no sign of anything on the interior but I'm not convinced it is the weather as it isn't anywhere else on the side of the house.

Any ideas please?

Owain_Moneysaver

It may be that side of the house just catches the cold/damp wind, or rain is running off the roof around the stack.

nickj_2

is it brickwork or is it rendered and painted, does that side get any sun , if not you will find that this time, of the year it will be damp most of the time and will result in green growth which can be removed with a fungicide wash- sandtex do a good one