Jim wrote:
Here is a question you likely don't see very often.

Old house that formerly had a coal bin. Cinder block wall blackened from
the coal. What is a good cleaner that won't harm the wall?

Seems like shop vac and brush, then 409. ? Is it unpainted ?
I had a coal bin too. I don't remember residue.

Since I don't know what's in the vicinity, hard to say.

Greg