It won't be flamable and it will sort of bake on when the fire is lit .
If it is thick enough , it should chip off with an old chisel . Don't whack it with a hammer though , just a little tap and scrape with the chisel in an out of the way area .
Failing that , a wire brush should do the job , and then repaint !
I take it you did read the cement instructions ( albeit after application ) , were there no instructions as to removing surplus glue , ie solvent / water etc .
Is there not a website for the glue/cement product ?