Hearthstone Heritage issue look see...

[Rearscreen]

My friend just got this stove and was concerned after 6 fires and proper break in what is going on with
the bubbling on the back of the stove. Installer said it's "cement" . Any opinions?

 

[begreen]

The installer is correct. It should disappear after a few hot fires. There may be a little black puddling below the stove but that too is temporary.