Cleaning dashed walls
Try sodium hyperchorite the liquid they use to shock swimming pools.
But be very carefull using this stuff.
I don't mean to be nannying you, but you net to make sure you don't get any on you.
Cover up youself, completely and watch you dont get it on any plants etc.
Dilute some in a bucket with some water (trial & error).
Brush it on with a stiff broom leave it for say 15-20 min
Then power wash it off
When washed down and wait till dry,then treat with a funguscide