"That's why I love painting outdoors," he added. "I think a lot of other artists love that as well.
"I'm probably exaggerating that I'm exhausted because of actually working, but I think it is more chatting.
"I've probably done more chatting the last five days than I have all year."
More than 100 people stopped him in one day
The artwork has been commissioned by Central BID Birmingham with the support of Network Rail.
Mr Murals, who has previously painted Osbourne in black and white, also spent more than 200 hours creating the Peaky Blinders mural on the walls of Digbeth Loc Studio.
It will be done in time for the band's Villa Park gig
Black Sabbath formed in Aston in 1968.
Their final gig will also features dozens of other heavy metal legends, including Metallica, Pantera and Anthrax.
