I have an issue with this - if you apply even half an inch of cement over someone, far too little to be stable, the proportions and features will change significantly, hence removing likeness. Also, a cement casing would not spread evenly over someone's features, but rather tend to smoothen them out.
How thick would the casing have to be to be stable anyway?
While avoiding the Medusa clichee is commendable, as written it is not feasible.
The "evil witch/wizard who encases people in stone" is an oldie (I'm instantly reminded of both Medusa and the White Witch from Narnia), but this is well-written enough to be a classic homage rather than a cheap copy.
Items (Melee Weapons) (Magical)