What is the black stain on my exterior brick, and how can I remove it?
The brick wall above my apartment is blackened, what is it?


It is caused by water leaking from that drainpipe. It is some form of mould that thrive in damp conditions.


  And is it possible to clean it?


Yes, a stiff-bristled brush and hard effort will make a big difference.

You can probably experiment with various chemicals, such as diluted bleach, to kill the mould.

If you do not repair the drainpipe, the problem will return in some months time, perhaps after winter or seasonal rain.

You can buy sealants that are intended for use on brick which prevent water penetration and which might help prevent this. They will alter the appearance of the brick though. This only works if the water is coming from the outside, not if the pipe with the leak is internal to the brickwork.