Any clues to what this is, how to remove it, or if I need to call a professional? There was a black something (fungus?) growing where the chimney meets the fireplace when we bought the house a year ago but cleaners removed it. Just had some chimney people in and they pressure washed the chimneys before waterproofing them outside. I think that rapid influx of a lot of water must have got something going.
Hi @mpostle - It is hard to see detail in the photo, to see its structure, but so far it looks like it could be a slime mould aka a myxomycete. If it is a slime mould, then please note that it is harmless, won't hurt surfaces or structure, and that it is not a fungus. It is fruiting on the surface only. - Reasoning: The dark colour, the suggestion of a bit of slime trail, the presumed lack of source of fungal food, and the sort of skin appearing at top right. This idea presumes some moisture availability increase in the junction between chimney and fireplace If however it is a fungus, that would mean the body of the fungus is living in something in the junction between chimney and fireplace, if there is anything in there that a fungus could live on(in) e,g. wood. Is that possible in that spot? - Reasoning: Another interpretation of the photo is that this is a puffball-type of fruiting body emerging from fungal habitat in than junction, and that the black is powdery spore mass and the sort of skin at top right is remainders of the external rind of puffball. If possible to get closer shots to show detail that will likely help with ID.
